Table of Content

18 July 2018, Volume 29 Issue 7

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Community characteristics and stability analysis of secondary deciduous broad-leaved forest in Mopan Mountains, Jilin Province, China.

LU Long-long, GUO Zhong-ling, FAN Chun-nan, ZHENG Jin-ping

2018, 29(7):  2079-2087.  doi:10.13287/j.1001-9332.201807.006

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The secondary deciduous broad-leaved forests in northeastern China were generally regenerated from the disturbed broad-leaved Korean pine forests, which are widely distributed in Changbai Mountains area. To understand their composition, structure and stability, a 5.76 hm²(240 m × 240 m) forest plot was established in the Mopan Mountains, Jilin Province in 2005, following the standards of the Center for Tropical Forest Science (CTFS). In this study, we analyzed the species composition, size class structure, survival curves of the main tree species and community stability of all woody plants with DBH ≥1 cm. The results showed that a total of 13368 individuals with DBH ≥1 cm were found, belonging to 39 species, 31 genera and 19 families. There were 12 species with importance value ≥1. The species composition was complex, with obvious characteristics of mixed broad-leaved forest. The abundance varied significantly among different species. The rare species and occasional species accounted for 23.1% and 43.6% of the total number of the species, respectively. The size distribution of all individuals showed a reverse “J” shape, which indicated that the community was in a stable and normal growth status. Fraxinus rhynchophylla, Quercus mongolica, Acer mono, and Maackia amurensis out of the six major species fitted reverse “J” form, Juglans manshurica showed an approximately normal distribution, and Ulmus japonica showed a “L” shape distribution. The survival curves of the six major tree species showed that the populations of F. rhynchophylla, Q. mongolica, A. mono, and M. amurensis were stable, J. mandshurica was declining, and U. japonica was growing. Results from the stability analysis of M-Godron indicated that the community was relatively stable at present.

Effects of climate change, fire and harvest on carbon storage of boreal forests in the Great Xing’an Mountains, China.

HUANG Chao, HE Hong-shi, LIANG Yu, WU Zhi-wei

2018, 29(7):  2088-2100.  doi:10.13287/j.1001-9332.201807.036

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Climate change will increase the frequency of fire disturbances, which may further exa-cerbate carbon loss from boreal forests in the Great Xing’an Mountains, China. In this study, we coupled forest ecosystem and forest landscape models to simulate the dynamics of boreal forest carbon storage in the next 100 years. We quantified the effects of climate change, fire and harvest on carbon storage of boreal forests. The results showed that climate change would increase carbon storage of boreal forests in the Great Xing’an Mountains, even if fire and harvest could partially offset such changes. Aboveground and soil organic carbon storage would increase by 9%-22% and 6%-9% in the next 100 years. In the short-term (0-20 years), the effects of climate change on carbon storage was stronger than fire. The effects of climate change on boreal forest carbon storage were less than fire and harvest in medium (30-50 years) and long-term (60-100 years). The variability of climate change and fire disturbance in the Great Xing’an Mountains caused high uncertainty of the future boreal forest carbon storage. The uncertainties of aboveground and soil organic carbon of boreal forests in the Great Xing’an Mountains were 12.4%-16.2% and 6.6%-10.4% in the next 100 years. The effects of seed dispersal, fire and harvest should be taken account for accurate estimation of carbon storage in Chinese boreal forests.

Community structure and leaf trait diversity in a vulnerable species, Phoebe chekiangensis (Lauraceae).

LU Yun-feng, PEI Nan-cai, ZHU Ya-jun, BAI Zhi-liang, YANG An-na, ZHANG Jun-hong, LOU Lu-huan, TONG Zai-kang

2018, 29(7):  2101-2110.  doi:10.13287/j.1001-9332.201807.013

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Phoebe chekiangensis, as one original species of ‘Nanmu with golden tint’, harbors limited natural distribution regions, which is recognized as a vulnerable species in China under nationwide protection. Under the background of global climate change, it is of scientific significance to study the community structure and diversity of the natural populations of P. chekiangensis. In this study, community structure, species diversity and the phenotypic variation leaf traits in the communities of thirteen residue natural populations were analyzed. A total of 235 vascular species from 162 genera and 87 families were found in 16 plots within 13 natural populations, including 221 seed plants from 151 genera and 79 families. The species diversity in tree layer of community in Kaihua, Zhejiang and Linan, Zhejiang was significantly lower than that of other communities due to severe disturbance, while intermediate disturbance promoted the species diversity of shrub layer in community in Jianning, Fujian, and slight disturbance was beneficial to natural regeneration of P. chekiangensis. Foliage phenotype was important for species identification within Phoebe genus. There existed substantial variation in foliage phenotypic diversity among and within populations. The mean coefficient of variation was 17.2%, ranging from 10.4% to 27.5%. The variation was greater among populations (53.6%) than within populations (17.0%). Mean phenotypic differentiation coefficient was 75.1% among populations, indicating that the variance among populations was the main source for the phenotypic variation of the species. Results from the cluster analysis indicated that the 13 natural populations were divided into two distinct groups based on the Euclidean distance (10 cm), with stochastic variation.

Decade dynamics of species composition and diversity of mountaintop mossy dwarf forest on the Yangming Mountains, Hunan Province, China.

CHEN Yan-hua, LONG Yue-lin, PENG Zhong-hua

2018, 29(7):  2111-2120.  doi:10.13287/j.1001-9332.201807.040

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Three monitoring plots were established in the Yangming Mountains mossy dwarf forest concentration zone in the Yangmingshan National Nature Reserve in Hunan Province in 2005. The changes of species composition and diversity during 2005-2016 were analyzed from species numerical characteristics, species importance value, diameter class structure, height structure, and species diversity. The results showed that from 2005 to 2016, the individual number for ≥1.0 cm diameter at ground height (DGH) in tree layer decreased by 30.9%. Viburnum dilatatum decreased greatest with 98.6%, and Rhododendron fortunei decreased least with 1.8%. Species richness was increased, and evenness was decreased. Except for R. fortunei, the importance values of all the species decreased significantly after ten years, indicating that R. fortunei was the dominant species in the dwarf forest. The diameter-class distribution of species in the dwarf forest was arranged at 1 cm level. The density of small-diameter (1 cm≤DGH＜6 cm) species was higher, but that of medium-diameter (6 cm≤DGH＜15 cm) and large-diameter (15 cm≤DGH) was lower. The diameter-class distribution of R. fortunei exhibited a reversed ‘J’ shape, and the height of community increased from 2005 to 2016, indicating the population had a stable and well-developing trend. The other species were poorly renewed and their diameter-class structure was irregular. Generally, the Patrick and Menhinick richness indices and the Simpson index were increased, and the Shannon and Pielou indices were decreased during the ten years.

Early effects of forest harvesting gap on understory plant diversity of three different plantations in Baiyun Mountain, China.

DU You-xin, LIU Wei, WANG Jun-feng, YOU Gen-biao, YE He-jun, LIAN Fa-liang, HE Xiao-yong

2018, 29(7):  2121-2128.  doi:10.13287/j.1001-9332.201807.035

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Pinus massoniana, Cunninghamia lanceolata, and Phyllostachys edulis are the main afforesting species in the low hilly areas and valley of the southern Yangtze River for commercial purpose. Ecological problems such as the monotonous community structure and low biodiversity are common in these plantations. To understand the effect of forest harvesting gap on the understory plant diversity in the three plantations, different size gaps with identical habitats were conducted with cano-pies as control in the three plantations in Baiyun Mountain. The life form spectrum of plants and plant diversity were compared among the different forest gaps. The results showed that species richness was the highest in C. lanceolata plantation (57 species), followed by P. edulis plantation (53 species) and P. massoniana plantation (41 species) in two years after harvesting. In the early period, plant species were more abundant in the gaps than that in the controls in C. lanceolata and P. edulis plantations, but there was no significant difference between the gaps and the control in P. masso-niana plantation. The percentage of phanerophyte plants were significantly higher in the forest gaps covered 500 m² area than that with other sizes. The percentage of the hemicryptophyte and therophyte plants were higher in the forest gaps covered 250 m² area. The percentage of geophyte plants were higher in the forest gaps with 50 m² area than the others. The resembling coefficients between the different size gaps were higher than that between the gaps and the control in the same plantation. The resembling coefficients between different size gaps in the same plantation were higher than that between different size gaps in different plantations. The resembling coefficients between the gaps and the control in different plantations were generally lower than the others. The species richness, Simpson ecological dominance index, and Shannon diversity index differed significantly for different size gaps. Except for Simpson ecological dominance index, the indices were significantly influenced by the plantation types. The effects of the interaction between plantation types and gap sizes on these indices were not statistically significant. Forest harvesting gaps altered life form spectrum of understory plants and increased plant diversity in the three plantations

Effects of temporal and spatial variation of canopy structures and light conditions on population characteristics of Fargesia decurvata.

HUANG Hui-min, DONG Rong, HE Dan-ni, XIANG Yun-rong, ZHANG Xiao-jing, CHEN Juan, TAO Jian-ping

2018, 29(7):  2129-2138.  doi:10.13287/j.1001-9332.201807.025

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The canopy structures and light conditions and the population characteristics of Fargesia decurvata, a dominant understory species, were investigated in three typical communities, i.e., deciduous broad-leaved forest, evergreen and deciduous broad-leaved mixed forest, evergreen broad-leaved forest. The results showed that with the succession from deciduous broad-leaved forest to evergreen and deciduous broad-leaved mixed forest and to evergreen broad-leaved forest, the Shannon index, Simpson index and Pielou index were increased, suggesting that the development of communities in Jinfo Mountains tended to be stable. Moreover, canopy structures were significantly changed, in that the canopy openness and mean leaf angle decreased, leaf area index increased, and canopy extinction ability enhanced, resulting in the decrease of light intensity under the canopy. The upper canopy was the main contributor for canopy closure, with the crown depth and crown area of canopy being the two main influencing factors. Moreover, canopy structures were significantly correlated with light conditions in the forest, with the greatest influence on the diffuse solar radiation. With the growth season coming, canopy openness and understory light conditions were decreased, while leaf area index increased, and their maximum values appeared in June or July in the three forest types. The maximum and minimum value of mean leaf angle appeared in spring and summer, respectively. Clonal growth of F. decurvata was closely related to canopy structures and light conditions. In evergreen and deciduous broad-leaved mixed forest with moderate light, F. decurvata grew best, with high and thick ramets, high ramet density (29.69±1.68 ind·m^-2) and high ability to expand rhizomes. In deciduous broad-leaved forest, the strong light condition caused the reduction of soil water might have effects on the growth of F. decurvata. However, in the evergreen broad-leaved forest with low light condition, ramets of F. decurvata tended to be short and thin, with low ramet density (5.80±1.16 ind·m^-2) and the clonal expansion ability. Those results suggested that forest succession would change canopy structures and understory light conditions. Low understory light conditions prohibited the regeneration and development of F. decurvata population.

Heterogeneity and optimal sampe size of soil physicochemical properties in subtropical forest.

ZHANG Guang-jie, CHAO Lin, ZHANG Wei-dong, WANG Si-long, YU Xin, ZHENG Wen-hui

2018, 29(7):  2139-2148.  doi:10.13287/j.1001-9332.201807.018

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Selecting the optimal sample size accurately is important for improving the measurement precision of soil physicochemical properties. In this study, we examined the within-site heterogeneity of soil physical and chemical properties in an evergreen broad-leaved forest and a Chinese fir (Cunninghamia lanceolata) plantation in subtropical China. We applied both traditional and bootstrapping technique to determine the optimal sample size, the number of observation (n), for predicting soil nutrient content with an allowable error of 10% at a 95% confidence level for both forest types. The results showed that soil pH and C/N had low variation, while the soil nutrients had a moderate variation in both forests. The coefficients of variation (CV) of total element concentration in the evergreen broad-leaved forest, such as total carbon and total nitrogen, were significantly larger than those in the Chinese fir plantation, while the CVs of available nutrients were similar between two forests. The evaluation error of all soil properties in two forests showed a stable trend after a sharp decline with the increase of sample size. The mean values also changed from violent fluctuation to stable, and extravagant sample could not effectively improve the accuracy of mean value measurement. The sample sizes of soil water content, total carbon, total nitrogen, nitrate (NO₃^--N), total potassium, total calcium, and total magnesium in the evergreen broad-leaved forest were signifi-cantly larger than those in the Chinese fir plantation, while the sample size for ammonium (NH₄⁺-N) showed opposite pattern, and the others had no significant difference. In addition, the sample sizes of different soil physicochemical properties varied significantly in the same forest. The available elements, such as NH₄⁺-N and NO₃^--N, needed a larger sample size than total elements in both forests. Accordingly, we proposed that the heterogeneity and sample size of soil physicochemical properties should be considered before soil survey. An adequate sample size may be varied according to the purpose of sample and the site-specific variation of soil characters.

Characteristics of soil organic carbon and its fractions in subtropical evergreen broad-leaved forests along an urbanization gradient.

XI Dan, KUANG Yuan-wen

2018, 29(7):  2149-2155.  doi:10.13287/j.1001-9332.201807.026

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Subtropical evergreen broad-leaved forests were selected along an urban (Guangzhou) - suburban (Dinghushan) - rural (Huaiji) gradient in the Pearl River Delta, from which soil samples in different layers were collected. The changes in total organic carbon (TOC), recalcitrant organic carbon (ROC), and active organic carbon (AOC) including readily oxidizable organic carbon (ROOC), microbial biomass carbon (MBC), and water-soluble organic carbon (WSOC) of samples were examined along this urbanization gradient to reveal the influence of urbanization on forest soil organic carbon. Results showed that no significant differences in both TOC and ROC contents were observed in 0-5 cm soil layer along the gradient. In 5-60 cm soil layer, the TOC content was significantly higher in the rural forest than that in the suburban and urban forests, the ROC content was the highest in the suburban forest and no significant difference was observed between the urban and rural forests. The ROOC content was significantly lower in the suburban forest than in the rural (0-60 cm soil layer) and urban (0-10 cm soil layer) forests. The MBC content was significantly lower in the urban forest than that in the suburban and rural forests. The suburban forest had significantly lower WSOC than the urban forest (0-10 cm soil layer). In 0-20 cm layer, the percentage of AOC to TOC of the urban and rural forests was significantly higher than those of the suburban forest, while the percentage of ROC to TOC was the lowest in the rural forest. The significant difference in the percentage of ROC to TOC was only observed in 5-10 cm depth layer between the suburban and urban forests. The results indicated that urbanization increased the active components of soil organic carbon and reduced the stable ones, which could be detrimental to organic carbon accumulation in soils. The rural forest soils were more sensitive to the urbanization.

Characteristics of soil phosphorus fractions of different vegetation types in subtropical forests and their driving factors.

ZENG Xiao-min, FAN Yue-xin, LIN Kai-miao, YUAN Ping, ZHAO Pan-pan, CHEN Yi-ran, XU Jian-guo, CHEN Yueh-min

2018, 29(7):  2156-2162.  doi:10.13287/j.1001-9332.201807.019

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Soil P fraction, microbial biomass P (MBP), and activities of acid phosphomonoesterase (ACP) and phosphodiesterase (PD) were analyzed under evergreen broad-leaved forest, mixed forest and coniferous forest in Daiyun Mountains. The results showed that labile-P comprised only 1.0%-4.5% of soil total phosphorus (TP). The ratio of soil carbon to organic phosphorus (C:Po) was >200, indicating phosphorus limitation across the three vegetation types. Organic phosphorus (Po) was a significant fraction of soil P, which accounted for 44.8%-47.1% and 28.6%-30.6% of TP in A and B horizons, respectively. Results from the redundancy analysis showed that the changes in P fractions were mainly driven by PD in the A horizon and by ACP in the B horizon. Moreover, the activities of PD and ACP had a significant negative correlation with Po. The results suggested that phosphorus deficiency occurred in the three vegetation types, and that PD and ACP could play major roles in the depletion of soil Po in response to phosphorus limitation in subtropical forests.

Effects of natural vegetation restoration and afforestation on soil carbon and nitrogen storage in the Loess Plateau, China.

LIU Yu-lin, ZHU Guang-yu, DENG Lei, CHEN Lei, SHANGGUAN Zhou-ping

2018, 29(7):  2163-2172.  doi:10.13287/j.1001-9332.201807.005

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Changes in land use can have important impacts on soil carbon and nitrogen storage. To explore the effects of different land use types on soil carbon and nitrogen storage, we examined the differences of soil carbon and nitrogen storage, ratio of carbon to nitrogen and root biomass in the 0-100 cm soil layer of the natural grassland and Pinus tabuliformis plantation since the implementation of the project (15 years) of “Returning Farmland to Forest (Grassland)” in the Ziwuling forest region of the Loess Plateau, China. The results showed that soil organic carbon of both natural grassland and P. tabuliformis plantation showed surface polymerization effect. Soil organic carbon storage in the 0-20 cm soil layer of natural grassland was significantly lower than that of P. tabuliformis plantation, while the other soil layers showed no significant difference. The total soil carbon storage of P. tabuliformis plantation in the 0-100 cm soil layer was 117.94 Mg·hm^-2, which was 28.4% higher than that of natural grassland. There was no significant difference in total nitrogen storage in different soil layers of the two vegetation types. The soil total nitrogen storage of natural grassland was 7.69 Mg·hm^-2 in the 0-100 cm soil layer, which was 17.7% higher than P. tabuliformis plantation. There was significant difference in ammonium storage among different soil layers in natural grassland and P. tabuliformis plantation. The ammonium storage in natural grassland was significantly higher than that in P. tabuliformis plantation, exhibited first increase and then decrease trend with the increases of soil depth. Only in the 0-20 cm soil layer, nitrate storage in natural grassland was significantly higher than the P. tabuliformis plantation. The ratio of carbon to nitrogen of natural grassland and P. tabuliformis plantation showed no significant difference in 0-20 cm soil layer. With the increases of soil layers, the ratio of carbon to nitrogen in P. tabuliformis plantation were higher than in the natural grassland, and the difference increased gradually. In addition, soil carbon and nitrogen storage showed significantly positive correlation with root biomass in natural grassland and P. tabuliformis plantation. Therefore, natural grassland was conductive to the accumulation of soil nitrogen storage, and P. tabuliformis plantation was beneficial to increase soil carbon storage. Root was an important factor affecting the distribution of soil carbon and nitrogen storage.

Effects of detritus removal on soil carbon, nitrogen and phosphorus stoichiometry and related factors in a temperate deciduous forest in the Maoershan Mountain, China.

KONG Qing, WANG Chuan-kuan, WANG Xing-chang

2018, 29(7):  2173-2182.  doi:10.13287/j.1001-9332.201807.015

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A detritus-removal experiment was conducted in a temperate deciduous broad-leaved forest in 2007 at the Maoershan Ecological Station in Northeast China, including two treatments: Litterfall removal (NL), root removal (NR). Soil water content, bulk density and the concentrations of soil C, N and P were measured in 2016. The results showed that the C concentration at the surface soil layer (0-10 cm) was reduced by 15.6% and 10.7% for the NL and NR treatments, respectively, while the weighted-mean soil C concentration in 0-30 cm depth was reduced by 7.9% and 4.6%, respectively. The N concentration of the surface layer in the NL treatment decreased by 10.2%, whereas the surface-soil P concentration in the NR treatment increased by 6.6%, resulting in reduced C:P and N:P for both treatments. The standardized major axis regressions showed that the regression slopes between the C, N and P at each layer of 0-30 cm soil depth differed significantly among the treatments. The intercepts of the regressions between soil C concentration and bulk density or soil water content had significant differences among the treatments. The results suggested that detritus-removal caused a coordinated variation in soil C, N and P stoichiometry and physical properties. Therefore, we recommend taking the effect on soil ecological stoichiometry into account in future detritus-removal experiments.

Effects of light-felling on non-growing season greenhouse gas emission from soils in Korean pine forests in Maoer Mountains, China.

ZHANG Yue, MU Chang-cheng, LIU Hui, JING Li-jie

2018, 29(7):  2183-2194.  doi:10.13287/j.1001-9332.201807.028

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Non-growing season soil greenhouse gas emission may play an important role in the forest ecosystem carbon and nitrogen cycle. However, it is not clear about the effects of the cutting distur-bance on soil greenhouse gas emissions during non-growing season. The CO₂, CH₄ and N₂O fluxes and related environmental factors (soil temperature, water content, carbon and nitrogen, etc.) were monitored in the Korean pine plantation (fifty year-old) under different light-felling manners (control, no cutting; the half light-felling, cutting 50% of broad-leaved trees in canopy; the whole light-felling, cutting 100% of broad-leaved trees in canopy), using static chamber technique and gas chromatography during non-growing season in Maoer Mountains of China. The main aim was to reveal the influence of cutting disturbance on soil greenhouse gases emission during non-growing season and its controlling factors. The results showed that the whole and half light-felling manners significantly decreased CO₂emission flux by 21.0% and 22.8%, and N₂O by 23.5% and 11.2%, and decreased CH₄uptake by 16.0% and 16.4%. The contribution of non-growing season CO₂, CH₄ and N₂O emission to annual total was 11.7%-14.2%, 13.1%-17.0% and 63.9%-72.6%, respectively. Light-felling manners decreased annual cumulative contribution of CO₂ by 1.4%-2.5%, that of CH₄ by 0.7%-3.9%, but increased that of N₂O by 2.4%-8.7%. Furthermore, light-felling increased the correlations of soil CO₂ fluxes with soil temperature, soil water content, nitrate and ammonium, and decreased its correlation with soil organic carbon content. Light-felling increased the correlations of soil CH₄ flux with soil water content, soil pH, soil organic carbon, ammonium, and decreased its correlation with nitrate. Light-felling increased the correlations between soil N₂O flux and soil temperature, decreased the correlations with nitrate and ammonium, and changed the positive correlation with soil pH to negative. Therefore, light-felling had significant effects on the emission fluxes of the greenhouse gas during non-growing season, with the whole light-felling decreased more soil N₂O emission flux than the half light-felling.

Effects of water and nitrogen coupling under drip irrigation on tree growth and soil nitrogen content of Populus ×euramericana cv. ‘Guariento’.

YAN Xiao-li, JIA Li-ming, DAI Teng-fei

2018, 29(7):  2195-2202.  doi:10.13287/j.1001-9332.201807.007

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By using surface drip irrigation, a field experiment including nine drip irrigation and fertigation treatments was carried out, with non-irrigation and non-fertilization as control (CK), to evaluate the integrative effects of water and nitrogen management on the increment of diameter, tree height, and stem volume, and the total nitrogen content in the 0-60 cm soil layer in the poplar (Populus ×euramericana cv. ‘Guariento’) plantations. There were three irrigation levels (irrigation was initiated when soil water potentials at 20 cm soil depth reached -75, -50 and -25 kPa) and three levels of nitrogen addition (150, 300 and 450 g·tree^-1·a^-1). Surface drip irrigation and fertigation treatments were applied in the gro-wing seasons of 2012 and 2013. The results showed that the combined treatments of water and nitrogen addition significantly increased growth and stem volume of the poplar plantation. In the first year of the experiment, the annual increment of stem volume was 11.54 m³·hm^-2·a^-1 in high water and high fertilizer treatment (soil water potentials of -25 kPa + nitrogen addition of 450 g·tree^-1·a^-1), which was 44.1% higher than that in the CK (8.01 m³·hm^-2·a^-1). In the second year, the annual increment of stem volume was 27.85 m³·hm^-2·a^-1 in medium water and high fertilizer treatment (soil water potentials of -50 kPa + nitrogen addition of 450 g·tree^-1·a^-1), being 36.0% higher than that in CK (20.48 m³·hm^-2·a^-1). The successive combined treatments signi-ficantly increased the total N content in the 0-20 cm soil layer, with total N content of each soil layer in the first and second year of the experiment being 12.3%-59.4% and 71.1%-81.1% higher than CK, respectively. The increments of diameter and tree height were significantly positively correlated with soil total N content. Nitrogen addition and the interactive effects of water and nitrogen addition significantly affected the diameter and height of trees and soil N content, while irrigation showed no significant effect. In conclusion, the combined drip irrigation and fertigation significantly increased growth and stem volume of the poplar plantation by promoting the soil fertility especially nitrogen availability in the topsoil.

Effects of precipitation reduction on the composition and stability of soil organic matter in a young Cunninghamia lanceolata plantation.

ZHOU Jia-cong, LIU Xiao-fei, JI Yu-huang, ZHANG Qiu-fang, ZHENG Yong, CHEN Yueh-min, YANG Yu-sheng

2018, 29(7):  2203-2210.  doi:10.13287/j.1001-9332.201807.001

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It is hard to predict the response of soil organic matter (SOM) to global climate change due to its heterogenous chemical structure. With the development of molecular techniques to identify the structure, sources and stages of SOM degradation, long-standing questions regarding the composition and stability of SOM might be resolved. To investigate the effects of changes in precipitation patterns on the stability of SOM, we analyzed the specific compositions and extent of degradation of SOM using biomarkers, in a young Cunninghamia lanceolata plantation after reducing 50% of precipitation (P) for two years. The results showed that precipitation reduction (P-treatment) significantly reduced the levels of free lipids. Relative to control (CT), P-treatment decreased short-chain n-alkanoic acids (C_16-18) and terpenoids and steroids by 62.8% and 19.1%, respectively. However, P-treatment did not significantly change the concentrations of other aliphatic compounds. Although there was no observable difference in the total lignin content between treatments, P-treatment significantly reduced the acid to aldehyde ratios for syringyl [(Ad/Al)s] and vanillyl [(Ad/Al)v]. Thus, the labile compositions of SOM were accelerated to decomposition under rainfall pattern change. Although the recalcitrant compositions (lignin) were relatively stable, their long-term stability should be further monitored.

Responses of soil invertase and urease activities to warming and plant removal during the growing season in an alpine scrub ecosystem.

MA Zhi-liang, ZHAO Wen-qiang, LIU Mei, ZHU Pan, LIU Qing

2018, 29(7):  2211-2216.  doi:10.13287/j.1001-9332.201807.008

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To understand the effects of climate warming and vegetation disturbance on soil ecological process during different stages of growing season in the alpine scrub ecosystem, the responses of soil invertase and urease activities to warming (0.6-1.3 ℃) and plant removal were investigated in a Sibiraea angustata scrubland on the eastern Qinghai-Tibetan Plateau, China. The results showed that experimental warming significantly increased soil invertase activity by 3.7%-13.3% in the removal- and unremoval-plant plots throughout the entire growing season. Warming significantly increased soil urease activity by 10.8%-56.3% in the removal- and unremoval-plant plots, except the late growing stage, during which warming had no significant effect on soil urease activity in the unremoval-plant plots. The effects of plant removal treatments on soil invertase and urease activities varied with warming and growing stages. Plant removal significantly decreased soil invertase activity of the warmed plots during the entire growing season and the unwarmed plots during the early and late growing stages, but did not affect soil invertase activity in the unwarmed plots during the mid-growing stage. Plant removal only significantly decreased soil urease activity by 10.5% in the unwarmed plots during the late growing stage. However, in the warmed plots, plant removal significantly decreased soil urease activity by 16.0%-18.7% during the early and mid growing stages. The results would increase our understanding of soil carbon and nitrogen cycling process in the alpine scrub ecosystems.

Effects of precipitation exclusion and warming on soil soluble carbon and nitrogen in a young Cunninghamia lanceolata plantation

YUAN Shuo, YANG Zhi-jie, YUAN Xiao-chun, LIN Wei-sheng, XIONG De-cheng, YANG Yu-sheng

2018, 29(7):  2217-2223.  doi:10.13287/j.1001-9332.201807.003

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Soil soluble carbon and nitrogen play important roles in soil carbon and nutrient cycles and are highly sensitive to climate change, as they can be directly used by microorganisms. We used Tension Lysimeter to collect soil solution in 50% precipitation exclusion (P) and warming (5 ℃) plus 50% precipitation exclusion (WP) treatments in a 2 year-old Cunninghamia lanceolata plantation in subtropics, to examine the effects of precipitation and temperature on soil soluble carbon and nitrogen concentrations in soil profile. Results showed that neither P treatment nor WP treatment changed seasonal dynamics of soil dissolved organic carbon (DOC) concentration, with maximum value at October among all treatments. DOC concentration was increased in both P and WP treatments in the whole soil profile, especially in 60 cm soil depth. Compared with the control, DOC concentration was increased by 30.4%-88.7% and 32.8%-137.6% in P and WP treatments, respectively, with the most obvious difference being found in October. DOC concentration was decreased with the increases of soil depth in the control, but no significant difference among different soil layers were found in P and WP treatments. NO₃^--N concentration was increased by 221.1%-931.0% in WP treatment. Therefore, precipitation reduction might increase losses of C and N from soil solution in subtropical forest, due to improvement of soil permeability by the increases of fine roots grown into deep soil, which might stimulate soil microorganism activities and soil organic matter decomposition. Furthermore, warming would exacerbate the risk of C and N losses.

Changes of total phenols and condensed tannins during the decomposition of mixed leaf litter of Pinus massoniana and broad-leaved trees.

QIN Yu, ZHANG Dan-ju, LI Xun, ZHANG Yan, YUAN Ya-ling, WANG Li-feng, PANG Zhi-hui, ZHANG Jian

2018, 29(7):  2224-2232.  doi:10.13287/j.1001-9332.201807.038

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A field litterbag experiment was conducted to investigate dynamics of total phenols and condensed tannin in the mixed leaf litter of Pinus massoniana (P) with other three broad-leaved species, i.e., Sassafras trumu (S), Cinnamomum camphora (C), Toona sinensis (T) during decomposition in low hilly lands, Sichuan Province, China. The mass ratio of P. massoniana : S. trumu (PS) was 6:4, 7:3, 8:2, P. massoniana : C. camphora (PC) was 6:4, 7:3, 8:2 and P. massoniana : T. sinensis (PT) was 6:4, 7:3, 8:2, respectively. The results showed that the degradation rate of condensed tannin in pure P. massoniana litter was 84.4%, being significantly lower than that in the mixed litters after 180 d. The degradation rate of condensed tannin and total phenols were the highest in PC 6:4, with 90.3% and 68.6%, respectively. The mixed litters promoted the decomposition of condensed tannin and total phenols in the P. massoniana litter. With decomposition time, the degradation rate of condensed tannin in mixed litters between P. massoniana and broad-leaved species initial increased, and then remained stable. The degradation rate of total phenols in pure P. massoniana litter, PT 7:3 and all the PC treatments increased significantly and then decreased during the 90 d decomposition. The degradation rate of total phenols in all the PS, PT 6:4 and 8:2 treatments increased with the decomposition time. The dynamics of total phenols and condensed tannin were closely related to litter quality, and the enzyme activities of polyphenol oxidase, peroxidase and leucine aminopeptidase.

Effect of litterfall input on soil respiration and its temperature sensitivity in moso bamboo forest under simulated drought.

GE Xiao-gai, TONG Ran, CAO Yong-hui, ZHOU Ben-zhi, XIAO Wen-fa, WANG Xiao-ming, LU Ren-fang

2018, 29(7):  2233-2242.  doi:10.13287/j.1001-9332.201807.033

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Increases in drought frequency and intensity under climate change will have great impacts on the carbon cycle of forest ecosystems. Understanding the responses of soil respiration and its temperature sensitivity to drought is necessary, when we assess whether soil is a carbon sink or source. The effects of litterfall input on soil respiration, temperature sensitivity and its lagging effect were studied in moso bamboo forests under simulated drought by ceiling method in the field with three litterfall treatments, i.e., ambient litterfall (unchanged, LU), litter addition (LA) and litter removal (LR). The results showed that LU decreased annual soil respiration rate in drought treatment (2.34 μmol·m^-2·s^-1), compared with that in the control (3.15 μmol·m^-2·s^-1) with ambient natural rainfall. LR showed stronger effect on soil respiration than LA. Compared with LU, LR decreased soil respiration rate by 21.0% in ambient condition and by 20.9% in drought treatment, while LA led to 5.3% increase only in drought treatment. Such a result indicated that the effects of LA and LR on soil respiration rate were stronger than LU in the drought condition. Drought decreased the temperature sensitivity of soil respiration by 8.4%, while LA and LR reduced that by 15.4% and 7.6%, respectively. The cumulative CO₂ emissions during the whole 18 months were 7.35 and 5.40 kg CO₂·m^-2 in the control and drought treatment. Compared with LU, LA increased the cumulative CO₂ emissions by 1.8% and 10.7%, and LR decreased that by 19.9% and 18.0% in the control and drought treatments. Our results indicated that the relationship between the litterfall amount (addition or removal) and soil respiration rate was nonlinear. The significant lagging effect may be caused by the decrease in root growth and microbial activity due to decreased soil water availability in drought treatment. Litterfall played a more important role in soil CO₂ emission under drought, and thus litterfall was a crucial factor in soil carbon emission in the context of climate change.

Effects of simulated nitrogen and sulfur deposition on litter decomposition rate in an evergreen broad-leaved forest in the Rainy Area of Western China.

TIE Lie-hua, FU Rao, ZHANG Shi-bin, ZHOU Shi-xing, HAN Bo-han, HUANG Cong-de

2018, 29(7):  2243-2250.  doi:10.13287/j.1001-9332.201807.012

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To examine the effects of nitrogen and sulfur deposition on litter decomposition rate, a one-year field experiment was conducted with the litter bag method from April 2013 to April 2014 in an evergreen broad-leaved forest in the Rainy Area of Western China. There were nine treatments with three nitrogen levels and three sulfur levels, including control (CK), low nitrogen deposition (LN, 50 kg N·hm^-2·a^-1), high nitrogen deposition (HN, 150 kg N·hm^-2·a^-1), low sulfur deposition (LS, 200 kg S·hm^-2·a^-1), high sulfur deposition (HS, 400 kg S·hm^-2·a^-1), low nitrogen and low sulfur deposition (LNLS), high nitrogen and low sulfur deposition (HSLS), low nitrogen and high sulfur deposition (LNHS), and high nitrogen and high sulfur deposition (HNHS). The results showed that the leaf litter residual rate ranged from 57.0% to 70.7% after one year decomposition. The time of half mass loss ranged from 1.47 to 2.08 years, while the time of 95% mass loss ranged from 6.33 to 9.01 years. Nitrogen deposition had no significant effect on litter decomposition rate. The decomposition rate was significantly increased in LS treatment but significan-tly reduced in HS treatment. The rate was significantly affected by LNHS and HNHS, but unaffected by LNLS and HNLS. In addition, simulated nitrogen and sulfur deposition interacted to affect litter decomposition rate, with antagonistic effects between nitrogen deposition and low-sulfur composite deposition and synergistic effects between nitrogen deposition and high-sulfur composite deposition. In conclusion, sulfur deposition and the combined nitrogen and sulfur deposition affected leaf litter decomposition rate in the evergreen broad-leaved forest, with consequences on the litter decomposition process.

Effects of soil moisture on litter decomposition of three main tree species in Northeast China.

CHENG Chun-xiang, GUO Kun, MAO Zi-jun, SUN Peng-fei, MA Hong-da, WANG Cheng

2018, 29(7):  2251-2258.  doi:10.13287/j.1001-9332.201807.030

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The effects of soil moisture variation on the litter decomposition of main tree species Betula platyphylla, Abies nephrolepis and Pinus koraiensis were evaluated in a primary forest of Korean pine (P. koraiensis) in Fenglin National Nature Reserve of the Northeast China, based on the measurements of surface (0-10 cm) soil moisture from 1998 to 2017. The results showed that litter decomposition rates increased with the increase of litter quality. The order of litter decomposition rate was B. platyphylla > A. nephrolepis > P. koraiensis at the same soil moisture. The litter decomposition rates decreased with the decrease of soil moisture. The sensitivity index of litter decomposition rates on soil moisture (M₁₀) were 0.782, 0.789 and 0.827, respectively, for B. platyphylla, A. nephrolepis and P. koraiensis. The initial litter decomposition rate decreased by 21.8%, 21.1% and 17.3% for B. platyphylla, A. nephrolepis and P. koraiensis, respectively, when soil moisture decreased by 10%. The decomposition rates of high-quality litter (high nitrogen content, low carbon to nitrogen ratio, and low lignin content) were more sensitive to the variation of soil moisture. The difference in decomposition rate among different litter types was reduced with the decrease of soil moisture. In the recent 20 years, the average soil moisture presented a significantly decreasing trend, which would inhibit litter decomposition in the primary Korean pine forest. Under the scena-rios of global change, soil moisture would further decrease with the increase of air temperature. It would definitely intensify the inhibitory effect on litter decomposition, and partly offset the enhanced effects of increased air temperature.

Short-term effects of litter treatment on soil C and N transformation and microbial community structure in Erythrophleum fordii plantation.

LUO Da, SHI Zuo-min, LI Dong-sheng

2018, 29(7):  2259-2268.  doi:10.13287/j.1001-9332.201807.031

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In southern subtropical China, the seasonal variations of soil carbon (C) and nitrogen (N) transformation rates and microbial community structure under different litter treatments (control, litter removal, litter double) in Erythrophleum fordii plantation were studied by the methods of barometric process separation (BaPS) and phospholipid fatty acids (PLFAs) profiles. The results showed that there were significant seasonal variations in soil respiration and gross nitrification rates under different litter treatments, with significantly higher rates in the rainy season than in the dry season. In the initial stage of litter treatment, soil respiration and gross nitrification rates decreased with increasing litter inputs. With prolonged litter treatment, both of them increased with increasing litter inputs. The total microbial PLFAs and each microbial group PLFAs under different litter treatments were significantly higher in the dry season than those in the rainy season. The fungal PLFAs/bacterial PLFAs in the rainy season were significantly higher than that in the dry season. In the dry season, litter removal significantly increased the total microbial PLFAs, bacterial PLFAs, fungal PLFAs and arbuscular mycorrhizal fungal (AMF) PLFAs by 30.9%, 28.8%, 44.4% and 31.6%, respectively. In the rainy season, litter removal significantly decreased the bacterial PLFAs and AMF PLFAs by 10.6% and 33.3%, respectively. Soil microbial community structure was affected by both litter input treatments and seasons. Soil temperature and NH₄⁺-N were the key determinants influencing the microbial community structure. The litter input treatments in E. fordii plantation had significant impacts on soil C and N transformation rate and microbial community structure in short-term, which were dependent on seasons.

Effects of different land use patterns on the soil microbial community diversity in montane region of eastern Liaoning Province, China.

DENG Jiao-jiao, ZHU Wen-xu, ZHOU Yong-bin, YIN You, BAI Xue-jiao, ZHANG Hua-zhe, ZHANG Yu-meng, QIN Sheng-jin

2018, 29(7):  2269-2276.  doi:10.13287/j.1001-9332.201807.009

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An experiment was conducted to examine the differences of soil microbial diversity across different land use patterns in montane region of eastern Liaoning Province, China. The relationships between soil physicochemical properties and soil microbial diversity in five different land use types, including Quercus mongolic forest, shrubland, Larix gmelinii plantation, Pinus koraiensis plantation, and Zea mays cropland were analyzed by Biolog-Eco method. The results showed that both soil total C and N contents were the highest in the Q. mongolica forest, which were 57.74 and 4.40 g·kg^-1, followed by shrubland, but only 17.46 and 1.31 g·kg^-1 in the Z. mays cropland, respectively. There were significant differences in microbial utilization rate of different land use types. The carbon utilization capacity by soil microbial communities was following the order of Q. mongolica forest > shrubland > L. gmelinii plantation > P. koraiensis plantation > Z. mays cropland, indicating that soil microbial metabolism and activity in Z. mays cropland were the lowest. The Shannon diversity index (2.997), Simpson diversity index (0.942) and McIntosh diversity index (5.256) of soil microbial community in the Z. mays cropland were significantly lower than those in other ecosystems. The average absorbance value (AWCD) was associated with Simpson diversity index and McIntosh diversity index. Esters, alcohols and amines were the primary carbon sources for the differentiation, which might be due to a joint action of many factors such as litter, soil nutrients, and specific soil microorganisms. The soil nutrient and soil microbial community diversity in forest land after reclamation sharply decreased, causing the loss of soil fertility and productivity. The region should keep the Q. mongolica forest, which could help restore soil fertility.

Change pattern of heartwood of Larix olgensis plantation.

JIA Wei-wei, ZHU Fei-yan, LI Feng-ri

2018, 29(7):  2277-2285.  doi:10.13287/j.1001-9332.201807.017

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Based on the data of 1179 discs and whorls of 49 trees from larch (Larix olgensis) plantations located in Mengjiagang forest farm in Heilongjiang Province, China, we analyzed the longitudinal variation pattern of heartwood radius. The results showed that the heartwood radius decreased with the increases of tree height, which was basically the same as the trunk shape. The relationship between the xylem radius (XR), diameter at breast height (DBH) and cambial age (CA) with the heartwood radius was significant. The stepwise regression analysis was used to develop heartwood radius (HR) and heartwood area (HA) models: HR=b₁+b₂XR²+b₃CA+b₄XR, HA=b₁+b₂DBH·XR+b₃CA+b₄DBH·XR². We used the evaluation statistics such as AIC, BIC, Log Likelihood and Likelihood ratio test to compare the heartwood radius and heartwood area models which fitted with the plot effect and tree effect. The heartwood radius and heartwood area models with parameters b₁, b₂, b₃ as mixed effects performed best when the tree effect was considered. The prediction accuracy of the mixed model was better than that of the basic model. In the application, the total heartwood radius and area could be predicted by the mixed model. Beta regression model was used to simulate the heartwood proportion. In this model, all parameters were significant, and the coefficients of determination were relatively high, with a good simulation effect.

Effects of drought stress on C, N and P stoichiometry of Ulmus pumila seedlings in Horqin sandy land, China.

WANG Kai, SHEN Chao, SUN Bing, WANG Xiao-nan, WEI Dong, LYU Lin-you

2018, 29(7):  2286-2294.  doi:10.13287/j.1001-9332.201807.020

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To understand the effects of drought stress on C, N and P stoichiometry in different organs of Ulmus pumila, U. pumila seedlings were grown under suitable water level, mild, moderate and serious water stress treatment, i.e., 80%, 65%, 50% and 35% of field water holding capacity. The results showed that drought stress increased C content in leaves, stems, coarse and fine roots, N content in leaves, stems and coarse roots, and P content in fine roots, but decreased P content in leaves, stems and coarse roots. Moreover, C:N in leaves and stems decreased, while C:P and N:P in leaves, stems and coarse roots increased and in fine roots reduced in response to drought stresses. There were significant correlations of C content among different organs, while N content was not correlated with P content in all organs. Soil water content was negatively related to C content in all organs, N content in leaves, P content and C:N in fine roots, C:P and N:P in leaves, stems and coarse roots. There were positive relationships between the soil water content and N content in fine roots, P content in leaves, stems and coarse roots, C:P and N:P in fine roots. These findings indicated that the absorption and upward translocation of N and P of U. pumila seedlings were influe-nced by drought stress. Nitrogen limitation for the growth of U. pumila seedlings was found. With the increases of drought stress, however, P limitation was gradually enhanced.

Simulation on photosynthetic light-responses of leaves of Quercus variabilis and Robinia pseudoacacia under different light conditions.

LI Li-yuan, LI Jun, TONG Xiao-juan, MENG Ping, ZHANG Jin-song, ZHANG Jing-ru

2018, 29(7):  2295-2306.  doi:10.13287/j.1001-9332.201807.029

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Photosynthesis can reflect the responses of plants to environmental changes. In this study, photosynthetic light-response curves were measured by the Li-6400XT photosynthetic system in Quercus variabilis and Robinia pseudoacacia plantations in Xiaolangdi Forest Ecosystem Research Station. Photosynthetic light-response curves were fitted by Ye model. The differences of photosynthetic parameters between inner and margin forests were examined. Stomatal conductance (g_s) light-response curve were fitted using the mechanism model of g_s coupled with a modified model of light-response of photosynthesis. The light-response characteristics of g_s were investigated. Net photosynthetic rates (P_n) of Q. variabilis in the inner forest was higher than that in the margin. The initial light efficiency (α) was 12.4% more in the inner forest than that in the margin in July and August when photosynthetically active radiation was less than 200 μmol·m^-2·s^-1. The ability to capture and utilize weak light of Q. variabilis leaves in the inner forest was obviously higher than that in the margin. When photosynthetically active radiation was higher than 200 μmol·m^-2·s^-1, P_n of Q. variabilis leaves in the margin forest was larger than that in the inner. Under weak light conditions (0-200 μmol·m^-2·s^-1), P_n of R. pseudoacacia in the inner forest was higher than that in the margin. P_n of R. pseudoacacia in the inner forest was less than that in the margin when light intensity was higher than 200 μmol·m^-2·s^-1. The dark respiration rate (R_d) and light compensation point (I_c) in the inner forest were 50.0% and 42.8% lower than those in the margin. The less R_d and I_c of the inner forest could reduce carbon loss and adapt to low photosynthetic rate. The stomatal conductance light-response of R. pseudoacacia in the inner forest significantly differed from that in the margin. The leaves of Q. variabilis and R. pseudoacacia had strong adaptability to the changes of light condition. The values of maximum net photosynthetic rate (P_{n max}) and α of Q. variabilis leaves were mainly controlled by g_s, and R_d and I_c were primarily affected by air temperature. P_{n max} and α of R. pseudoacacia leaves had significant positive correlation with air temperature. The I_c and the light saturation point (I_s) were remarkably correlated with leaf saturation vapor pressure deficit.

Provenance difference in growth traits and photosynthetic characteristics of Acer catalpifolium seedlings under different shading conditions.

LYU Cheng-yu, LIU Yan-hong

2018, 29(7):  2307-2314.  doi:10.13287/j.1001-9332.201807.022

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Acer catalpifolium is a unique species and wild endangered one in China. Currently, no research has addressed its endangered status from the perspective of photosynthetic characters. The photosynthesis characteristics and growth rate of A. catalpifolium seedlings from four provenances (Dujiangyan, Dayi, Emeishan and Leibo) under two shading conditions (50% and 80% of full shade) were examined to explore the light response mechanism. The results showed that the net photosynthetic rate (P_n), stomatal conductance (g_s), transpiration rate (T_r) and water use efficiency (WUE) of A. catalpifolium seedlings from four provenances sharply decreased with the decreases of light intensity. When the light intensity was reduced, the light compensation point (LCP) and light saturation point (LSP) of A. catalpifolium seedlings from Dujiangyan and Emei-shan were all decreased, while those of the seedlings from Dayi increased, and those of the seedlings from Leibo showed no significant changes. Net photosynthetic rate and water use efficiency were positively correlated with plant height and crown growth. The effects of different light intensities on photosynthetic characteristics and growth rate of A. catalpifolium were significantly different. Low light availability under canopy might be the limiting factor for natural regeneration of A. catalpifolium populations from Dayi. Compared with other provenances, A. catalpifolium seedlings from Leibo were more shade requiring. A. catalpifolium had better light adaptability and growth performance from Dujiangyan and Emeishan, which could be used as high-quality source for transplant protection.

Effects of defoliation on the allocation of non-structural carbohydrates in roots of Fraxinus mandshurica seedlings.

WANG Wen-na, GAO Guo-qiang, LI Jun-nan, WANG Zheng-quan, GU Jia-cun

2018, 29(7):  2315-2322.  doi:10.13287/j.1001-9332.201807.024

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Global climate changes would lead to outbreaks of leaf-feeding insects. Leaf loss could reduce photosynthate production, with consequences on non-structural carbohydrates (NSC) storage and allocation in trees. In this study, the responses of NSC and its compartment concentrations in tap-, coarse- and the first to fifth order fine roots of 2-year-old seedlings of Fraxinus mandshurica to defoliation (40% loss of leaf area) were measured from June to October. The results showed that NSC and its compartment concentrations in roots exhibited distinct seasonal dynamics in both control and defoliation treatments. Following defoliation, NSC concentration decreased in tap- and coarse roots by 3.8% and 30.7%, respectively, while increased in the first five order roots by 1.2%-23.5%, to which starch contributed majorly for each root compartment. Soluble sugar concentration was enhanced by defoliation in tap- and coarse roots by 7.1% and 62.3%, respectively, but decreased in the first to fifth order roots by 2.7%-42.8%. Defoliation had different influences on starch and soluble sugar, with positive effects on the ratio of soluble sugar to starch concentrations in tap- and coarse roots but negative effects on the first to fifth order roots. Overall, defoliation decreased photosynthate production in leaves, leading to the remobilization of starch in tap- and coarse roots and the transportation as soluble sugar to fine roots, as well as the following storage in these roots, which would facilitate the resistance of fine roots to the low temperature in winter.

Short-term effects of nitrogen and water treatments on fine root order morphology of Machilus pauhoi seedlings.

ZOU Yu-xing, ZHONG Quan-lin, YOU Ya-ling, YU Hua, ZHENG Wen-ting, CHEN Jia-jing, CHENG Dong-liang

2018, 29(7):  2323-2329.  doi:10.13287/j.1001-9332.201807.014

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A factorial nitrogen and water addition experiment was carried out with one year-old Machilus pauhoi seedlings from Suichuan County, Jiangxi Province, with six treatments being established: two water levels with 80% and 40% of field moisture holding capacity and three nitrogen addition levels of 0, 50, 100 kg N·hm^-2. Specific root length, specific root area, average diameter and tissue density of three fine root orders of M. pauhoi were measured to understand the main and interactive effects of short-term nitrogen addition and drought stress on root characters of M. pauhoi seedlings. The results showed that average fine root diameter and specific root length differed significantly among fine root orders. With the increases of root orders, the average root diameter increased, with the maximum being present in the third order (0.97 mm), but specific root length decreased, with the minimum being present in the third order (238.99 cm·g^-1). No significant effects of nitrogen addition on specific root surface area, average fine root diameter, specific root length and root tissue density were observed. There were significant effects of water treatments on average fine root diameter, specific root length and root tissue density. Drought stress significantly increased average diameter of the third order fine roots of seedlings and decreased root tissue density of the first and second order fine roots. Specific root length of the third order fine roots in arid environments was significantly lower than that under the normal water supply condition. There was no interactive effects of nitrogen addition and drought stress on fine root morphology of M. pauhoi.

Growth responses of Castanopsis hystrix and Pinus massoniana plantations to throughfall reduction in subtropical China.

CHEN Lin, LIU Shi-rong, WEN Yuan-guang, ZENG Ji, LI Hua, YANG Yu-jing

2018, 29(7):  2330-2338.  doi:10.13287/j.1001-9332.201807.034

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To better predict and evaluate responses of tree growth and forest productivity to the changes of precipitation pattern and seasonal drought under global climate change scenarios, throughfall reduction experiments including 50% of throughfall and natural rainfall (control) treatments were conducted in Castanopsis hystrix and Pinus massoniana plantations of warm subtropical region over a three-year period (2015-2017). Diameter at breast height (DBH), litterfall production and leaf area index of both plantations were investigated, respectively. The results showed that throughfall reduction resulted in a 31.8% decrease of annual increment of DBH of C. hystrix in 2017 and had no significant impact on that of P. massoniana. Leaf area index under throughfall reduction decreased by 8.8% in C. hystrix plantation and decreased by 7.2% or remained unchanged in P. massoniana plantation. Branch litterfall in 2015 and total litterfall in 2017 of C. hystrix increased by 29.6% and 35.8% by throughfall reduction, but leaf litterfall of other tree species (except for P. massoniana) in P. massoniana plantation declined by 50.7% in 2015, with no significant difference for other litterfall components. In conclusion, throughfall reduction had consequences of drought stress in both C. hystrix and P. massoniana plantations, with inter-annual variation and inter-specific differences.

Time lag characteristics of the stem sap flow of Haloxylon ammodendron in the Minqin oasis-desert ectone, China.

YAO Zeng-wang, CHU Jian-min, WU Li-lu, YUAN Qi, DANG Hong-zhong, ZHANG Xiao-yan, GAN Hong-hao, JIANG Sheng-xiu

2018, 29(7):  2339-2346.  doi:10.13287/j.1001-9332.201807.023

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The stem sap flow rate of Haloxylon ammodendron plantation in the Minqin oasis-desert ectone was measured by the thermal dissipation probe (TDP). A cross-correlation analysis was used to estimate the time lag between the stem sap flow and the environmental factors influencing transpiration, including photosynthetically active radiation (PAR) and water vapor pressure deficit (VPD). The results showed that the stem sap flow rate of H. ammodendron had substantial seasonal variation, with the monthly average sap flow being the highest in June and the lowest in August. There was an obvious time lag between the stem sap flow of H. ammodendron and PAR and VPD. The stem sap flow was lagged behind PAR for 80 min but it was ahead of VPD for 114 min. Additionally, the time lag exhibited significant difference among different months during the growth season from May to September. The sap flow of H. ammodendron was more dependent on the variation of PAR on the daily scale than VPD, but it was more closely related to VPD during the day time. The time lag between the stem sap flow and PAR/VPD had no significant correlation with the tree factors (including plant height, ground diameter, diameter at 50 cm height, under branch height, canopy size) and the nocturnal sap flow.

Sap flow of Amorpha fruticosa in the secondary saline-alkali land in Ningxia Yellow River irrigation area, China.

CAO Qi-qi, WANG Ruo-shui, XIAO Hui-jie, YANG Ben-man, LIU Tao

2018, 29(7):  2347-2354.  doi:10.13287/j.1001-9332.201807.016

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From May to October in 2017, the sap flow, water consumption and the effects of environmental factors on the sap flow of Amorpha fruticosas with different stem diameters under different water and salt conditions were examined with the packaged sap flow measuring system in a secondary saline-alkali land of Ningxia Yellow River irrigation area. The sap flow rate showed a broad peak curve with no obvious phenomenon of ‘midday break’ in sunny days and a multi-peak curve in cloudy, overcast and rainy days. Weak sap flow was found at night. In the growing season (May - October), total sap flow of A. fruticosas with basal stem diameters of 13, 16 and 22 mm were 138.14, 206.06, 370.11 kg, respectively. The water consumption was largest in June and July, accounting for about 50% of the whole growing season, followed by May and August, and lowest in September and October. At both 0.5 h and day scales, photosynthetically active radiation (PAR) was the dominant meteorological factor affecting the sap flow. In the first growth stage (May 13th - August 19th), soil water in shallow layer (0-40 cm) had significant effect on the sap flow of A. fruticosas with three different diameters, and soil salt in shallow layer had significant inhibitory effect only on A. fruticosa with the diameter of 13 mm. In the second growth stage (August 20th - October 10th), soil water and soil salt had no significant effect on A. fruticosas with three different diameters. In summary, the A. fruticosas with diameters <13 mm was not suitable for planting in saline soil (electrical conductivity (EC)>2 dS·m^-1), and individuals with diameters >16 mm could grow well in saline soil (EC=5 dS·m^-1). Moreover, reasonable irrigation should be carried out in the vigorous growth stage of the A. fruticosas.

Relationship between radial growth of Abies georgei and climate factors at different altitudes on the eastern slope of Yulong Snow Mountain, China.

ZHANG Yun, YIN Ding-cai, TIAN Kun, HE Rong-hua, HE Mao-zhen, LI Yu-chun, SUN Da-cheng, ZHANG Wei-guo

2018, 29(7):  2355-2361.  doi:10.13287/j.1001-9332.201807.021

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Based on dendrochronological methods, we established residual chronologies (RES) of Abies georgei at low, middle and high altitudes with ring width data on the eastern slope of Yulong Snow Mountain. We examined the relationship between the radial growth and climate factors (temperature and precipitation) by response function analysis and redundancy analysis (RDA) to identify the key climatic factors driving the radial growth of A. georgei. The results showed that the responses of radial growth of A. georgei to climates were consistent at three altitudes, which was jointly controlled by temperature and precipitation. This consistency was related to the steep terrain of Yulong Snow Mountain, the high-altitude distribution, and shallow root characteristics of A. georgei. At all three altitudes, tree growth showed significantly positive correlation with mean temperature of the current July, mean temperature of the previous November, and precipitation of the current January, but negative correlation with precipitation of the current June. The comprehensive application of response function analysis and redundancy analysis could accurately reveal the relationship between tree growth and climatic factors along environmental gradients. Our results provided a scientific basis for climatic reconstruction and forest management in the area.

Dynamic response and variance of vegetation in China from 1982 to 2015 under the asymmetric rate of temperature fluctuation.

PANG Bo, ZHANG Peng-yan, LU Cheng-peng, HE Jian-jian, CEN Yun-feng, YAN Yu-hang, YANG Xiao-jie

2018, 29(7):  2362-2372.  doi:10.13287/j.1001-9332.201807.039

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The impact of global warming on the growth and development of natural vegetation is an important concern worldwide. Based on the data from the vegetation normalization index, daytime temperature (T_max), nighttime temperature (T_min), precipitation, and elevation from 1982 to 2015, we examined the day-night warming response of 42 types of natural vegetation in China. The results showed that both the temperature at day and night was significantly increased in the study area, with obvious asymmetry. The night warming was about 1.6 times as high as that at daytime. The T_min was more conducive to vegetation growth than the T_max. The proportion of vegetation types with positive relationship with T_min was greater than the T_max, with significant spatial difference. Subtropical vegetation accounted for 85.7% of vegetation with positive correlation with T_max. The temperate alpine, mountainous, and desert vegetation responded more positively to T_min. The increase of T_min was not conducive to the growth and development of vegetation at high altitudes, while that of T_max was the opposite. The correlations of vegetation growth with T_max and T_min were as follows: steppe > meadow > needleleaf forest > desert vegetation > broadleaf forest; meadow > desert vegetation > broadleaf forest > steppe > needleleaf forest.

Spatiotemporal variation of vegetation net primary productivity and its driving factors from 2000 to 2015 in Qinling-Daba Mountains, China.

WANG Yao-bin, ZHAO Yong-hua, HAN Lei, AO Yong

2018, 29(7):  2373-2381.  doi:10.13287/j.1001-9332.201807.010

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We analyzed spatiotemporal changes in vegetation net primary productivity (NPP) in the Qinling-Daba Mountains based on MOD17A3 data and driving factor data from 2000 to 2015. We used trend analysis, Hurst index, and correlation analysis to examine the effects of climate change, soil type, topographic factors, vegetation type, and human activities on NPP. With respect to spatial variation, NPP was the highest in southwestern area and lowest in the northeast. The temporal trend over the 16-year period showed that NPP was increased in the northwest and decreased in the northeast. The projected trend of NPP was of continuity in northern area and anti-continuity in southern area of the Qinling-Daba Mountains. NPP was positively correlated with precipitation and temperature. NPP in areas with dark-brown earths, yellow earths, purplish soils and paddy soils were significantly higher than those with other soil types. The spatial distribution and trends of NPP differed among vegetation types. High NPP mainly occurred on slopes of 25° to 50° and altitudes of 500 to 1000 m or above 2500 m. Human activities had both positive and suppressive effects on NPP.

Reconstruction of July NDVI over 172 years based on tree-ring width of Larix chinensis in Taibai Mountain Nature Reserve, China.

ZHU Xian-liang, LI Shu-heng, BAI Hong-ying, HOU Li, CHEN Lan, QIN Jin

2018, 29(7):  2382-2390.  doi:10.13287/j.1001-9332.201807.002

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We used the correlation analysis of Larix chinensis tree-ring width chronologies, meteorological data as well as regional NDVI data to reconstruct the NDVI sequence variation of the north and south aspects of Taibai Mountain Nature Reserve in the recent 172 years. The results showed that the NDVI variation of Taibai Mountain Nature Reserve was consistent with plant growth dyna-mics. Hydrothermal condition in growing season was the dominant factor controlling NDVI changes. Tree-ring width was significantly positively correlated with NDVI in growing season. The strongest correlation occurred in July. Thus, we used the long time series of tree ring width index in July to reconstruct the regional historical period variation of NDVI sequence. The results demonstrated that historical changes of July NDVI sequence existed five dense periods and five sparse periods. Further analysis indicated that these periods corresponded with the climate change trends and drought events. The reconstructed July NDVI sequence of both northern and southern slopes of Taibai Mountain Nature Reserve highlighted the existence of quasi periodic variation of 60 years.

Retrieval of leaf area index of Phyllostachys praecox forest based on MODIS reflectance time series data.

ZHU Di-en, XU Xiao-jun, DU Hua-qiang, ZHOU Guo-mo, MAO Fang-jie, LI Xue-jian, LI Yang-guang

2018, 29(7):  2391-2400.  doi:10.13287/j.1001-9332.201807.011

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Based on the MODIS surface reflectance data, five vegetation indices, including norma-lized difference vegetation index (NDVI), simple ratio index (SR), Gitelson green index (GI), enhanced vegetation index (EVI) and soil adjusted vegetation index (SAVI) were constructed as remote sensing variables, coupled with the seven original spectral reflectance bands of MODIS. Stepwise regression and correlation analysis were used to select the variables, and the stepwise regression and Back Propagation (BP) neural network models were constructed based on the measured LAI to retrieve the LAI time series data of Phyllostachys praecox (Lei bamboo) forest during the period from January 2014 to March 2017. The retrieval results were compared with MOD15A2 LAI products during the same period. The results showed that SR was the single variable selected for the stepwise regression model. The correlations of LAI with bands b₁, b₂, b₃, b₇ and five vegetation indices were significant, which could be used as input variables of BP neural network model. There was a significant correlation between the LAI estimated from BP neural network and measured LAI, with the R² of 0.71, RMSE of 0.34, and RMSE_r of 13.6%. R² was increased by 10.9%, RMSE decreased by 5.6%, and RMSE_r decreased by 12.3% compared with LAI estimated from stepwise regression method. R² was increased by 54.5%, RMSE decreased by 79.3%, and RMSE_r decreased by 79.1% compared with MODIS LAI. The LAI of Lei bamboo forest could be accurately retrieved using BP neural network method based on MODIS reflectance time series data, which would be a feasible method for rapid monitoring of LAI in Lei bamboo forest.

Age investigation and growth history analysis of old trees in Nyemo County of Tibet, China.

JIA Heng-feng, MOU Yu-mei, DANZENG Luo-bu, LI Yan

2018, 29(7):  2401-2410.  doi:10.13287/j.1001-9332.201807.032

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Investigating age and growth histories of old trees is important for census and document of old trees in China. In this study, we analyzed the age and growth histories of 20 old trees of Juglans regia and 10 old trees of Sabina tibeticain Nyemo County, Tibet, China, using dendrochronological methods. The results showed that 4, 7 and 9 J. regia trees were identified as Class Ⅰ, Ⅱ and Ⅲ to protection, and 2, 4 and 4 S. tibetica trees as Class Ⅰ, Ⅱ and Ⅲ to protection, respectively. Tree growth of both species was synchronized in the study area, especially during 1940s-1980s. There were substantial differences in the growth among individuals. Significantly positive correlation was found between the ring-width chronologies of the two tree species and Palmer drought severity indices (PDSI). Old trees were mainly distributed in villages and road sides, where human activities were frequent. In addition to the climatic factors, frequent human activities in the study area played an important role in affecting tree radial growth. It caused synchronous radial growth of the old trees between those two species and significant variation among different individuals. Both climate change and human activities should be considered to make the conservation plans for old trees in Nyemo County.

Distribution changes and refugia of three spruce taxa since the last interglacial.

ZHANG Ai-ping, WANG Yi, XIONG Qin-li, WU Xiao-gang, SUN Xiao-ming, HUANG Yan-meng, ZHANG Lin, PAN Kai-wen

2018, 29(7):  2411-2421.  doi:10.13287/j.1001-9332.201807.027

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Based on the current distribution information and 19 environmental variables data, we used the maximum entropy model to simulate the suitable distribution of Picea likiangensis var. likiangensis, P. purpurea and P. wilsonii in the last interglacial, Last Glacial Maximum, Mid- Holocene and present. The results from such modelling were validated by pollen data. We analyzed the relationship between species distribution dynamics and climate change, and then speculated the cryptic refugia of those species. Both the areas under the receiver operating characteristic curves and the verification results from pollen data indicated high accuracy of the model results. Results showed that isothermality was the most important factor influencing the distribution of P. likiangensis var. likiangensis and mean temperature of the warmest quarter was the most important for the distribution of both P. purpurea and P. wilsonii. Temperature was more important than precipitation in driving species distributions. Three species expanded their distribution ranges in Last Glacial Maximum due to their cold-adapted ecological habitat and the deep canyon topography feature which benefited their migration. There might be refugia of both P. wilsonii and P. purpurea in last interglacial, and they respectively located in Shennongjia Mountain in Hubei and Erlang Mountain and its nearby mountains in Sichuan. Our results, to some extent, made accurate prediction of the suitable distribution of three spruce species in the key periods since last interglacial, and speculated refugia of P. purpurea and P. willsonii. Our findings provided reference for better understanding of the formation mechanism of the present distribution of Picea and prediction of distribution changes in the future and sustainable management and protection of three spruce species.

Effects of changes in seasonal snow-cover on litter decomposition and soil nitrogen dynamics in forests.

WU Qi-qian, WANG Chuan-kuan

2018, 29(7):  2422-2432.  doi:10.13287/j.1001-9332.201807.004

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Changes in snow-cover patterns induced by global climate change profoundly influence ecological processes in terrestrial ecosystems, including litter decomposition and soil nutrient cycling. Forest, a major terrestrial ecosystem, plays a crucial role in global biogeochemical cycling. Here, we reviewed the effects of changes in seasonal snow-cover on litter decomposition and soil nitrogen (N) cycling in forests. Global climate change would result in increasing or decreasing seasonal snow-cover depending on local conditions, with direct and indirect effects on forest litter decomposition. The changes in seasonal snow-cover would directly affect decomposition process by changing environmental temperature and moisture, litter quality, and decomposer dynamics, and would indirectly influence decomposition via altering community structure, vegetation phenology, and soil nutrients. Meanwhile, the changes in seasonal snow-cover would modify forest soil N dynamics through changing N enrichment, soil temperature and moisture, freeze-thaw cycle, forest community, subnivean fauna and microorganisms. Further studies in this field should focus on: 1) employing experiments with divergent protocols to simulate diverse changing patterns of seasonal snow-cover under the global climate change scenarios; 2) the effects of the seasonal snowmelt leaching on forest litter decomposition and soil N dynamics; 3) elucidating mechanisms underlying forest litter decomposition and soil N dynamics driven by changes in seasonal snow-cover patterns in different ecosystems and climate zones; and 4) quantifying the instantaneous and prolonged effects of changes in seasonal snow-cover on forest litter decomposition and soil N dynamics in the snow-covered and snow-free seasons, respectively. These studies will provide theoretical basis and solid data support for the understanding and model-prediction of the responses of the biogeochemical cycle in terrestrial ecosystems to global climate change.

Ecological and physiological mechanisms of growth decline of Robinia pseudoacacia plantations in the Loess Plateau of China: A review.

WEI Jing-shu, LI Zong-shan, FENG Xiao-yu, ZHANG Yuan, CHEN Wei-liang, WU Xing, JIAO Lei, WANG Xiao-chun

2018, 29(7):  2433-2444.  doi:10.13287/j.1001-9332.201807.037

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Robinia pseudoacacia has been widely planted in the Loess Plateau of China for soil and water conservation. The growth decline of R. pseudoacacia plantations has become a recently emerging challenge for the revegetation program and sustainable forest management in this region. As to the scientific definition, identified criteria and quantitative indices have not yet been comprehensively quantified, our current understanding of the ecological and physiological mechanisms for growth decline of R. pseudoacacia plantations is limited. The knowledge could enrich the basic theories of vegetation restoration and benefit the sustainable development of the afforestation project in the Loess Plateau. Through the comprehensive compilation of literatures on forest decline and tree mortality in the Loess Plateau and other regions across the world, this review summarized the mechanisms and recent research progress on growth decline for R. pseudoacacia plantations in the Loess Plateau, primarily demonstrated from ecological (e.g., climatic change, soil desiccation, the imbalance of community structure and the misconduct of forest management) and physiological (e.g., hydraulic failure, carbon starvation, genetic and molecular regulation) perspectives. Finally, we highlighted the research gap with regard to growth decline of R. pseudoacacia plantations in the Loess Plateau.

Responses mechanism of C:N:P stoichiometry of soil microbial biomass and soil enzymes to climate change.

XU Miao-ping, REN Cheng-jie, ZHANG Wei, CHEN Zheng-xing, FU Shu-yue, LIU Wei-chao, YANG Gai-he, HAN Xin-hui

2018, 29(7):  2445-2454.  doi:10.13287/j.1001-9332.201807.041

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Microorganisms and soil enzymes are important drivers for biogeochemical cycles in terrestrial ecosystems. Understanding the role of microorganisms in the regulation of ecosystems and the response mechanisms of microbial biomass and soil enzymes to climate change are important topic in ecology. From the perspective of climatic factors, this review introduced the roles of microorganisms and soil enzymes in the carbon, nitrogen and phosphorus cycles of terrestrial ecosystems based on the theory of ecological stoichiometry. Moreover, we synthesized the responses mechanisms of soil microbial and soil enzyme stoichiometry, i.e., changes of microbial metabolic rate, enzymatic acti-vity, microbial community structure, ecological stoichiometry of soil microbial biomass and soil enzymes, and nutrient use efficiency. Finally, we analyzed the current research inadequacies and proposed the scientific problems in this field, i.e., to comprehensively elucidate the response mecha-nism of soil microbes and soil enzymes to climate change; to examine the nutrient coupling mechanism of soil microbes and extracellular enzymes; and to explore the adaptive strategies of C:N:P stoichiometry of soil microbial biomass and soil enzymes to climate change.