Table of Content

15 August 2023, Volume 34 Issue 8

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Relationship between carbon stock and the structure of coniferous and broad-leaved mixed forest in Tianmu Mountains, China

WU Dengyu, DOU Xiaowen, TANG Mengping

2023, 34(8):  2029-2038.  doi:10.13287/j.1001-9332.202308.015

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Taking the coniferous and broad-leaved mixed forest of Tianmu Mountain National Nature Reserve in Zhejiang Province as research object, we divided the tree species into three pairs, including evergreen and deci-duous species, broad-leaved and coniferous species, dominant and non-dominant species, to compare the difference of the individual tree carbon stock of each pair and analyze the diameter distribution pattern and tree height distribution pattern of carbon stocks. The relationship between spatial structure and individual tree carbon stock was analyzed by using spatial structure indicators including V_Hegyi competition index, complete mingling and aggregation index, to reveal the relationship between the structure of coniferous and broad-leaved forests and carbon stocks, and provide a theoretical basis for management of forest carbon sequestration. The results showed that the average individual carbon stock for evergreen and deciduous species, broad-leaved and coniferous species, dominant and non-dominant species were 57.7 and 87.4 kg, 54.6 and 74.7 kg, 67.4 and 48.1 kg, respectively. The individual tree carbon stock of evergreen species was significantly lower than that of deciduous species, the individual tree carbon stock of broad-leaved species was significantly lower than that of coniferous species, and the individual tree carbon stock of dominant tree species was significantly higher than that of non-dominant tree species. The diameter distribution and height distribution of carbon stock of each species group obeyed normal distribution. The V_Hegyi competition index was significantly negatively correlated with individual tree carbon stock, and it was consistent with the power function distribution. Both complete mingling and aggregation index were linearly and positively correlated with individual tree carbon stock. The direction of influence of different spatial structures on the individual tree carbon stock was consistent. The structure of coniferous and broad-leaved mixed forest had a significant impact on individual tree carbon stock. In the management of forest carbon sequestration and sink enhancement, it is necessary to regulate the unreasonable forest structure and promote its succession to the climax community in order to improve forest carbon stock.

Effect of gap size on the regeneration in Larix principis-rupprechtii plantation

ZHAO Yi, LI Fuming, ZHU Jingkang, CHANG Chenlong, FENG Yonghan, LIANG Wenjun, WEI Xi

2023, 34(8):  2039-2046.  doi:10.13287/j.1001-9332.202308.026

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We conducted a survey on seedlings (height <1 m) and saplings (height ≥1 m, diameter at breast height <5 cm) in 20 gaps of Larix principis-rupprechtii plantations on Guandi Mountains, Shanxi to analyze regene-ration density, growth indicators, and spatial distribution of L. principis-rupprechtii seedlings and saplings under four gap sizes (<60 m², 60-120 m², 120-180 m², and ≥180 m²). The results showed that growth indicators (ground diameter, height) of seedlings and saplings and regeneration density of seedlings were highest in small gaps (14-60 m²). The sapling regeneration density was highest in medium gaps (60-120 m²), and sapling density exceeded seedling density in each size category. L. principis-rupprechtii seedlings and saplings exhibited favorable regeneration in small and medium gaps, while large gaps (120-180 m²) and extra-large gaps (≥180 m²) were unfavorable for L. principis-rupprechtii regeneration. L. principis-rupprechtii seedlings and saplings were mainly distributed within the canopy projection area and along the edge of canopy gap area. Controlling gap size within the range of 14-120 m² through artificial interventions, such as planting and thinning, could promote the regeneration of L. principis-rupprechtii.

Effects of target tree management on understory regeneration in Pinus massoniana plantations

YIN Biran, XIANG Yongqi, LYU Qian, ZHANG Yan, CHEN Yuqin, CHEN Gang, LAI Jiaming, LI Xianwei

2023, 34(8):  2047-2054.  doi:10.13287/j.1001-9332.202308.016

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To clarify the effects of target tree management on natural forest regeneration, with Pinus massoniana plantations in the low mountainous regions of eastern Sichuan with target tree densities of 100, 150 and 200 trees·hm^-2 as test object, we analyzed the effects of management densities on canopy structure, plant diversity, and soil physicochemical properties on understory regeneration. The results showed that the regeneration index increased with management density, which increased 0.08-0.10 in the managed plantations compared with unmanaged sites. When the density of the target trees was 150 trees·hm^-2, an increase of 9 regeneration tree species and an increase of 800 trees·hm^-2 in quantity were observed. The dominance of herbaceous species was not prominent, but canopy structure was improved, and the regeneration ability of understory plants was enhanced. The impact of habitat factors on the regeneration index ranked as soil total porosity (0.591) > leaf area index (-0.536) > Shannon index (-0.085) > available P (0.053) > total N (-0.007) > Pielou index (-0.005). Target tree management facilitated understory regeneration in the P. massoniana plantations by improving soil pore conditions, reducing leaf area index, and decreasing herbaceous plant diversity index. A management density of 150 trees·hm^-2 was more sui-table for target tree management in P. massoniana plantations.

Comparison of species composition and community characteristics of Quercus forests on south and north slopes of Taibai Mountain, China

HUANG Ruizhi, WANG Qi, SUN Jingyi, YANG Shaowei, ZHAO Yipei, LIU Jianfeng, XIAO Wenfa

2023, 34(8):  2055-2064.  doi:10.13287/j.1001-9332.202308.003

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We examined species composition, community characteristics, diversity, and community similarity of five Quercus communities composed of three Quercus species (Q. variabilis, Q. aliena var. acutiserrata, Q. wutaishanica) on the altitudinal gradient on the south and north slopes of Taibai Mountain. The results showed that there was an altitudinal transition pattern from Q. variabilis pure forest to Q. variabilis-Q. aliena var. acutiserrata mixed forest, Q. aliena var. acutiserrata pure forest, Q. aliena var. acutiserrata-Q. wutaishanica mixed forest and Q. wutaishanica pure forest on the south and north slopes of Taibai Mountain. The main companion species of Quercus community on the north slope were Pinus armandii, Castanea seguinii, and Sorbus alnifolia, and were Pinus tabuliformis, C. seguinii, Carpinus cordata, and Q. spinosa on the south slope. Species richness, woody plant density, and Quercus species dominance on the north slope of Taibai Mountain were higher than those on the south slope. α diversity of tree layer in Quercus community on the south and north slopes of Taibai Mountain increased first, then decreased and then increased with altitude. α diversity of tree layer was higher in mixed forests than pure forests. α diversity of shrub layer was higher than that of tree layer and herb layer in Quercus community on south and north slopes. β diversity fluctuated greatly along the altitudinal gradient on the south and north slopes, indicating that species composition changed greatly with altitude. Results of redundancy analysis showed that mean warmest month temperature, altitude and tree height accounted for 79.0% of the community diversity on the north slope, and that soil water content, tree height, canopy density and mean annual temperature accounted for 79.6% of the community diversity on the south slope. Overall, Quercus dominance was higher on the north slope of Taibai Mountain, and the substitution distribution pattern of Quercus species was clearer than that on the south slope. Environmental factors related to temperature and precipitation jointly affected α diversity of Quercus communities.

Competition and synergistic mechanisms of species in Phyllostachys edulis-Alsophila spinulosa association based on niche theory

YANG Long, YAN Lingbin, AN Mingtai, XU Qin, YANG Man, YUAN Dongmei

2023, 34(8):  2065-2072.  doi:10.13287/j.1001-9332.202308.002

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We examined the niche characteristics and interspecific covariant relationship of main species in Phyllostachys edulis-Alsophila spinulosa association in Chishui A. spinulosa National Nature Reserve under P. edulis disturbance condition, and analyzed the mechanism of competition and coexistence across different species. The results showed that there were 67 species from 53 genera and 40 families in the association. The importance values, Shannon niche breadth index (B_S), and Levins niche breadth index (B_L) of P. edulis were the largest, indicating its absolute dominant status in association. The importance value and B_L of A. spinulosa ranked the second, while B_S was the third. There were 190 pairs of 20 main species. The niche overlap between P. edulis and A. spinulosa was the largest, with niche overlap value of 0.64. 71.6% of species pairs had niche overlap of less than 0.2, indicating low niche overlap and high degree of niche differentiation among species. The overall association of main species in association was significantly positive, and the community was relatively stable. The correlation among the main species was not significant, the linkage was not strong, and the species were independent from each other. P. edulis showed significant positive correlation with A. spinulosa, Brassaiopsis glomerulata, Ficus virens, and Mallotus barbatus, while P. edulis showed significant negative correlation with Mallotus philippensis, Cinnamomum glanduliferum, and Machilus gamblei. Niche difference and fitness between P. edulis and natives affected the coexistence and competition among species. Controlling the expansion of P. edulis and limiting the size of species with negative correlation with A. spinulosa could create a favorable living environment for A. spinulosa.

Effects of gravel on the evaluation of soil organic carbon density in Pinus massoniana plantations

JIAN Zunji, LEI Lei, NI Yanyan, ZHU Jianhua, ZENG Lixiong, XIAO Wenfa

2023, 34(8):  2073-2081.  doi:10.13287/j.1001-9332.202308.010

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Gravel (>2 mm) is one of the main parameters for estimating soil carbon pool. To assess the effects of gravel on soil bulk density (BD) and organic carbon density (SOCD) in Pinus massoniana plantations, we estimated the BD and SOCD at the 0-10, 10-20 and 20-40 cm soil depths of 131 plots under two different conditions, with and without removing gravel. The BD of each soil layer after removing gravel was 0.58-1.57, 0.60-1.67, and 0.59-1.75 g·cm^-3, respectively, which was significantly lower than that before removing gravel. Gravel increased the BD by 6.5%-6.8%. The SOCD of each soil layer before removing gravel was 8.93-65.97, 7.63-59.08, and 8.79-94.53 t·hm^-2, respectively, which was higher than that after removing gravel. Overall, by neglecting the effect of gravel, SOCD was overestimated by 4.9%-11.8%. As gravel content increased, the relative deviation in the estimated BD and SOCD among different methods increased. When the gravel content was higher than 20%, the estimated SOCD at soil layer of 0-40 cm showed a significant difference between neglecting gravel and removing gravel, with the former being 29.7%-47.4% higher than the latter. In conclusion, gravel markedly affected the estimations of BD and SOCD. It was recommended that SOCD should be estimated by the method that not only uses the BD after removing gravel but also considers gravel as a correction factor (especially when gravel content is above 20.0%) to avoid overestimation of soil carbon pool.

Understory fuel loads and the impact factors of Quercus mongolica natural secondary forest in Hebei Pro-vince, China

MA Yunhui, MA Changming, FENG Shuyao, GUO Yanpeng, LIU Bingxiang

2023, 34(8):  2082-2090.  doi:10.13287/j.1001-9332.202308.006

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We investigated understory fuel loads of Quercus mongolica natural secondary forests in Hebei Province, China. We analyzed the effects of stand factors, topographic factors, and ground cover factors on the quantity and composition of fuel, established the dynamic models of understory fuel loads, and proposed management measures. The results showed that the understory total fuel load in Q. mongolica natural secondary forests was 11.68 t·hm^-2, which exceeded the forest fire potential threshold (10 t·hm^-2). The understory dead fuel load was mainly humus, and the understory living fuel load was mainly shrubs. The 1 h time-lag fuel load increased significantly with increasing canopy density, stand density, stand age, and litter thickness. The 10 h time-lag fuel load increased signi-ficantly with increasing stand density, average tree height, and litter thickness. Humus load decreased significantly with increasing altitude and increased significantly with increasing humus thickness. Herb load increased significantly with increasing sunny slope orientation and herbal coverage. Shrub load increased significantly with increasing slope degree, shrub coverage, and humus thickness. Understory total fuel load decreased significantly with increasing altitude, and increased significantly with increasing stand density, humus thickness, and litter thickness. The results of stepwise regression analysis indicated that stand density, humus thickness, and altitude could better predict the understory total fuel load (R_adj²=0.775). Therefore, more attention should be paid on the control of stand density of Q. mongolica natural secondary forest in Hebei Province. Cleaning of litters and humus on the ground would help prevent forest fires scientifically and effectively.

Prediction models of fire spread rate of Pinus koraiensis plantation's surface fuel

REN Menglin, GUO Yan, CHEN Boxuan, FAN Jiale, HU Tongxin, SUN Long

2023, 34(8):  2091-2100.  doi:10.13287/j.1001-9332.202308.024

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Pinus koraiensis plantation has high fire risks due to high oil content in branches and leaves. The spread of surface fire is the main way of forest fire expansion. Understanding the surface fire spread rate can provide scientific guidance for fire fighting. We carried out a laboratory experiment with surface fuel of Pinus koraiensis plantation in Maoershan area of Heilongjiang Province. We set different levels of fuel moisture contents (5%, 15%, 25%), fuel loads (0.5, 0.7, 0.9, 1.1 kg·m^-2), and slope (0°, 10°, 20°, 30°, 40°) to simulate the characteristics of fuel bed in the field, and quantified the spread rate by thermocouple method. We further compared and analyzed the prediction accuracy of Rothermel model, modified Rothermel model and random forest model, and evaluated the optimal model for predicting the surface fire spread rate of P. koraiensis plantation. The results showed that the overall efficacy of directly using the Rothermel model to predict the surface fire spread rate of P. koraiensis plantations was good, but the prediction result of the spread rate under the conditions of high slope and high moisture content was not satisfied. The Rothermel model after refitting the slope parameters and the random forest model had good prediction efficacy and similar prediction accuracy. The random forest model needed to be further evaluated and verified due to its own characteristics. The modified Rothermel model was more suitable for predicting the surface fire spread rate of P. koraiensis plantations at a slope range of 0°-40° than the others.

UAV hyperspectral combined with LiDAR to estimate chlorophyll content at the stand and individual tree scales

YANG Tao, YU Ying, YANG Xiguang, DU Hongxuan

2023, 34(8):  2101-2112.  doi:10.13287/j.1001-9332.202308.004

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Chlorophyll is an important indicator of vegetation health status, accurate estimation of which is important for evaluating forest carbon sink. In this study, we estimated the chlorophyll content of coniferous forests, broad-leaved forests and mixed forest stands at stand and individual tree level by unmanned air vehicle (UAV) hyperspectral data combined with light detection and ranging (LiDAR) point clouds, which improved the non-destructive estimation accuracy of forest chlorophyll. We further comprehensively analyzed the spatial distribution of chlorophyll content at different scales. A total of 36 spectral characteristic variables related to chlorophyll content were screened by correlation analysis based on the fusion of UAV hyperspectral data and LiDAR point clouds combining with the empirical data from ground plots. We constructed multiple models for chlorophyll estimation by using statistical model, including multiple stepwise regression, BP neural network, BP neural network optimized by firefly algorithm, random forest and hybrid data-driven PROSPECT mechanism model. The optimal model was selected to estimate the chlorophyll content. The horizontal and vertical distribution of chlorophyll content at the stand level and individual tree level were analyzed. The results showed that the random forest model was superior to the models constructed by multiple stepwise regression, BP neural network and BP neural network optimized by firefly algorithm for chlorophyll estimation with R² and RMSE of 0.59-0.64 and 3.79-5.83 μg·cm^-2, respectively. The accuracy of the mechanism model was the highest, with R² and RMSE of 0.97 and 3.40 μg·cm^-2. The chlorophyll contents differed across stand types, with that in broad-leaved forest (25.25-31.60 μg·cm^-2) being higher than mixed forest (13.52-23.93 μg·cm^-2) and coniferous forest (6.40-13.71 μg·cm^-2). There were significant differences in chlorophyll contents the in vertical direction among different stands. For individual tree of different species, the chlorophyll content inside the canopy was lower than that outside the canopy in the horizontal direction. In the vertical direction, there was no difference in chlorophyll content among different layers of Pinus sylvestris var. mongolica canopy. However, significant differences were observed among the upper, middle, and lower layers of Juglans mandshurica canopy. Using the fusion of hyperspectral image and LiDAR point cloud data, the mechanism model driven by hybrid data could effectively improve the accuracy and stability of chlorophyll content estimation at different scales.

Effects of light environments within Cinnamomum camphora canopy on leaf functional traits and photosynthetic characteristics

LENG Hanbing, WAN Ninghai, LIU Qunlu

2023, 34(8):  2113-2122.  doi:10.13287/j.1001-9332.202308.027

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To explore the adaptive mechanism of leaf photosynthetic capacity in different light environments within Cinnamomum camphora canopy and enhance carbon sequestration, we investigated morphological structures, nutritional and physiological traits and photosynthetic characteristics of leaves in different orientations of C. camphora canopy, southern side in the outer layer (100% full light), southern side in the inner layer (34% full light) and northern side (21% full light). We analyzed the main limitation resulting in down-regulation of photosynthetic capacity in low light environments. Results showed that specific leaf weight, the thickness of lower and upper epidermal cuticle, lower epidermis, palisade tissue as well as cell number and width of palisade tissue, the thickness ratio of palisade to spongy tissue, cell structure closely degree significantly decreased with decreasing light intensity within canopy, opposite to the responses of spongy tissue thickness, cell length-width ratio of palisade tissue, and cell structure loose degree. The contents of leaf carbon, soluble protein, soluble sugar and starch were significantly lower in two low light environments compared with full light, whereas nitrogen content was markedly higher in north side. Low light prominently reduced gas exchange parameters, i.e., net photosynthetic rate (P_n), dark respiration rate, stomatal conductance to CO₂(g_sc), mesophyll conductance to CO₂(g_m), total conductance to CO₂(g_tot), intercellular CO₂ concentration (C_i), CO₂ concentration at the chloroplast (C_c). P_n was positively correlated with g_sc, g_m, g_tot and C_c. There were no differences in maximum quantum photochemical efficiency, actual quantum photochemical efficiency, photochemical quenching coefficient, maximum rate of Rubisco carboxylation (V_{c max}) and maximum rate of electron transport (J_max) among light environments. V_{c max} and J_max were positively correlated to P_n. Of the shading-induced limitations to photosynthesis, g_m limitation was the most important, and g_sc limitation was enhanced with further weakened light intensity while biochemical limitation was rather limited. In summary, the results suggested that full light could improve leaf photosynthetic potential in C. camphora canopy leaves, reduce the effects of g_m and g_sc limitation on photosynthesis, and consequently enhance carbon assimilation capacity.

Instantaneous sap flow velocity simulation of Euonymus bungeanus based on neural network optimization model

ZHOU Peng, HAN Lei, PENG Ling, LIU Lili, WANG Nana, MA Jun, MA Yunlei

2023, 34(8):  2123-2132.  doi:10.13287/j.1001-9332.202308.019

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The sap flow of trees is complex and difficult to express with multivariate linear or empirical models. A simple and feasible method on the basis of understanding sap flow variation to simulate its variation with environmental factors is of special importance for quantitatively analyzing forest ecohydrological processes and regional water demand. In this study, with one of the shelter forest species Euonymus bungeanus in the east sandy land of Yellow River in Ningxia as the research object, we continuously measured the trunk sap flow velocity by thermal diffusion sap flow meter, and analyzed the effects of environmental factors on stem sap flow. We used the particle swarm optimization (PSO) and sparrow search algorithm (SSA) optimized neural network model to predict sap flow velocity of E. bungeanus. Results showed that the main environmental factors influencing sap flow were solar radiation, vapor pressure deficit, air temperature, and relative humidity, with the influencing importance of 32.5%, 25.3%, 22.0% and 16.1%, respectively. The response process between sap flow and environmental factors presented a hysteresis loop relationship. The optimized BP, Elman and ELM neural network models improved the comprehensive evaluation index (GPI) by 1.5%, 30.0% and 5.3%, respectively. Compared with the PSO-Elman and SSA-ELM optimization models, the SSA-BP optimization model had the best prediction results with an improvement of 1.0% and 23.2% in GPI, respectively. Therefore, the prediction results of the BP neural network model based on the sparrow search algorithm could be used as an optimal model for predicting instantaneous sap flow velocity of E. bungeanus.

Constraints on the maintenance of wild Taxus cuspidata populations based on regression conservation

ZHU Weilin, XU Chao, LONG Ting, WU Xinlei, CHEN Jie, LIANG Yanjun, LI Jingwen

2023, 34(8):  2133-2141.  doi:10.13287/j.1001-9332.202308.005

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To clarify the key factors constraining the maintenance of wild Taxus cuspidata populations and to develop conservation strategies and technical links for current populations, we investigated the renewal status and distribution patterns of wild T. cuspidata populations in the main distribution areas of China. We analyzed the effects of stand factors and human disturbance on population renewal and maintenance. The results showed that the overall regeneration of wild T. cuspidata populations was poor. The basal diameter and height class structure of renewed individuals showed an unhealthy state. 19% of the area was well regenerated. There were three types of regeneration, including poor regeneration with few adult trees, poor regeneration with many adult trees, and good regeneration with few adult trees. The communities in which T. cuspidata was found could be classified into Abies nephrolepis + Tilia amurensis forest, spinney forest, and Picea jezoensis var. microsperma + A. nephrolepis forest. The renewal number of A. nephrolepis + T. amurensis forest was significantly higher than that of spinney forest. Increased stand density and moderate human disturbance contributed to the regeneration of T. cuspidata. The regenerating T. cuspidata seedlings increased significantly when stand density increased from low to medium. The number of regenerating populations in moderately disturbed habitats was significantly higher than those in lightly disturbed habitats. Human disturbance and habitat were currently critical constraints to maintaining and regenerating wild T. cuspidata populations. The conservation of T. cuspidata should consider current status of population regeneration in each habitat patch to develop corresponding in situ conservation and regression conservation measures and focus on the influence of critical factors such as disturbances and habitat conditions.

Impacts of reclamation marsh restoration on greenhouse gas emission in the Sanjiang Plain, China

ZHAO Yueqin, MA Xiujing, ZHAO Wanjing, ZHANG Zhijun, SUN Xiaoxin

2023, 34(8):  2142-2152.  doi:10.13287/j.1001-9332.202308.001

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To understand the variations in greenhouse gas fluxes during the process of returning cropland to wetland in the Sanjiang Plain, we selected naturally restored wetlands of 4, 7, 11, 16 and 20 years as research objects to compare with a cultivated site (soybean plantation for 13 years) and an uncultivated marsh dominated by Deyeuxia purpurea and Carex schmidtii. We measured carbon dioxide (CO₂) and methane (CH₄) fluxes using a static chamber-gas chromatography and explored the main influencing factors. The results showed that there were seasonal variations in growing-season CO₂ and CH₄ fluxes of the restored wetlands, with the seasonal trends in greenhouse gases becoming gradually similar to that of natural marsh with increasing restoration time. The mean growing-season CO₂ fluxes increased during the early stage of restoration, but then decreased during the late stage, which decreased from 893.4 mg·m^-2·h^-1 to 494.0 mg·m^-2·h^-1 in the 4-year and 20-year sites, respectively. Mean CH₄ fluxes increased with restoration time, ranging from a weak CH₄ sink (soybean fields, -0.6 mg·m^-2·h^-1) to a CH₄ source of 87.8 mg·m^-2·h^-1(20-year restored site). The CH₄ fluxes of experimental plots were consistently lower than that of natural marsh (96.4 mg·m^-2·h^-1). Increases in water level and soil conductivity resulting from restoration were the main driving factors for the decrease in CO₂ fluxes. The increases in water level and soil dissolved organic carbon resulting from restoration were the primary drivers for the increase of CH₄ fluxes in the restored wetlands. The global warming potentials increased with restoration time, ranging from 27.8 t·CO₂-eq·hm^-2(soybean fields) to 130.8 t·CO₂-eq·hm^-2(plot of 20-year restoration), which gradually approached that of natural marsh (156.3 t·CO₂-eq·hm^-2). The emission of GHGs from restored wetlands in the Sanjiang Plain gradually approached those of natural marsh. Further monitoring is required to identify the maturity of restored wetlands for achieving greenhouse gas emissions equivalent to that of natural marshland.

Soil and vegetation characteristics during the formation of typical Ligularia virgaurea degraded grassland

MA Jianguo, LI Yuman, WANG Shulin, ZHU Huaide, YAO Mengfan, WANG Xiaobo

2023, 34(8):  2153-2160.  doi:10.13287/j.1001-9332.202308.007

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To understand the formation process of typical poisonous plant degraded grassland, we studied the cha-racteristics of vegetation and soil during the gradual expansion of Ligularia virgaurea into the native grassland of Qinghai-Tibet Plateau. The results showed that population density, plant height, coverage, and biomass of L. virgaurea increased during the formation of L. virgaurea degraded grassland. In comparison with native grassland, the degraded grassland had higher total aboveground biomass (113.9%), soil total nitrogen concentration (61.0%), NH₄⁺-N (77.9%), organic carbon concentration (45.3%), available phosphorus concentration (78.8%) as well as soil microbial biomass carbon (42.1%) and nitrogen (47.4%), but lower NO₃^--N (40.1%) and species richness (28.5%) and aboveground biomass (45.7%) of other species beyond L. virgaurea. The extremely strong abilities of interspecific inhibition and morphological plasticity of L. virgaurea, as well as efficient nutrient accumulation and utilization were the keys to its successful expansion, which facilitated the formation of typical L. virgaurea degraded grassland.

Seasonal dynamics of soil nitrogen mineralization and their influencing factors during shrub anthropogenic introduction in desert steppe

LI Zhili, WANG Hongmei, ZHAO Yanan, ZHOU Yurong

2023, 34(8):  2161-2170.  doi:10.13287/j.1001-9332.202308.009

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We selected enclosed grassland, grazed grassland and shrublands with different planting years (3, 12, 22 years)/densities (intervals of 2, 6, 40 m) to investigate soil N mineralization dynamics in the growing season (April-October) and its influencing factors during the process of desert steppe-degradation-shrub introduction. The results showed that soil moisture at 0-200 cm layer was decreased with increases of shrub age and density, and that the variations of soil moisture at 0-10 cm layer coincided with seasonal change. Compared with grazed grassland and enclosed grassland, the positive effect of shrubs on soil carbon, nitrogen and phosphorus contents first increased and then decreased with the increases of age and density. Moreover, soil N mineralization significantly varied across months and sites. Soil NO₃^- content and microbial biomass carbon and nitrogen were significantly higher from June to August. The proportion of NO₃^- to inorganic nitrogen significantly increased from 30.5% in enclosed grassland to 69.5% in shrublands. NH₄⁺ content was mainly affected by months compared with sites. In the process of steppe-degradation-shrub introduction, the increases of shrub age and density significantly enhanced seasonal differences of soil nitrification and ammonification, but not on the seasonal mineralization of microbial biomass carbon and nitrogen. Soil NH₄⁺ and NO₃^- contents were significantly and positively correlated with total nitrogen, organic carbon and N/P. Soil stoichiometric ratios (C/N and N/P) directly regulated N mineralization process.

Meta-analysis on the effects of nitrogen deposition on soil N₂O flux in different habitats

KONG Dongyan, YANG Lingfang, DIAO Jingwen, GUO Peng

2023, 34(8):  2171-2177.  doi:10.13287/j.1001-9332.202308.013

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We carried out a meta-analysis to explore the effects of site characteristics (climatic factors and soil properties) and nitrogen (N) factors on soil nitrous oxide (N₂O) flux after N addition based on 290 data from 66 field N addition experiments in China. The results showed that mean annual precipitation, mean annual temperature, ambient N deposition rate, and soil C/N of sites were positively correlated with the increases of N₂O flux after N addition. Soil pH was negatively correlated with the increases of N₂O flux after N addition. Furthermore, soils in wetland ecosystem were most sensitive to N addition, followed by forest ecosystem, and grassland showed the lowest sensitivity. Among all the site characteristics, soil pH and C/N were the most important factors driving the responses of N₂O flux to N addition. Soil N₂O flux increased the greatest after nitrate addition. The increase of N₂O flux was similar after the addition of urea and ammonium, while N₂O flux increased the least when ammonium nitrate was added. In summary, to accurately assess and predict the response of soil N₂O flux to N deposition, the effects of site characteristics and N fertilizer types should be comprehensively considered.

Effect of humus on photodegradation of quinclorac under different fertilization modes

SHEN Die, DAI Jingyu, JI Yuefei

2023, 34(8):  2178-2184.  doi:10.13287/j.1001-9332.202308.014

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Humus is a specific kind of organic matter widely distributed in soils. The characteristics of humus have significant impacts on the fate of pollutants in the environment. In this study, we examined the effects of fertilization modes from rice rotation systems on the contents, spectral properties, photochemical activity, and photosensitization of quinclorac (QNC) of humic (HA) and fulvic acids (FA). The results showed that under the rice-vegetable rotation system, organic fertilizer treatment decreased the humification degree and molecular weight of HA, but increased the number of oxygen-containing functional groups and the abilities of photoproducing hydroxyl radical (HO·), singlet oxygen (¹O₂) and photosensitizing QNC, compared with chemical fertilizer treatment. Under organic fertilization mode, the molecular weight of FA was increased, but the number of redox functional groups and the abilities of photoinducing HO· and ¹O₂ and photosensitizing QNC were decreased. Under rice-shrimp cultivation system, organic-inorganic fertilizer treatment increased the humification degree, molecular weight, number of redox functional groups and oxygen-containing functional groups, and ¹O₂ photogeneration of HA, but decreased the abilities of photoproducing HO· and photosensitizing QNC, as compared with chemical fertilizer treatment. The humification degree and molecular weight of FA under organic-inorganic fertilization mode were increased, while the abilities of photoproducing HO· and ¹O₂ and photosensitizing QNC were decreased. In conclusion, organic fertilization could enhance the photochemical activity and photosensitizing efficiency of humus, and further promote the photodegradation of QNC in the environment.

Effects of elevated carbon dioxide (CO₂)and ozone (O₃)concentrations on ectoenzyme activities in rice rhizospheric soil

LENG Peng, WANG Jianqing, TAN Yunyan, SHAO Yajun, WANG Liyan, SHI Xiuzhen, ZHANG Guoyou

2023, 34(8):  2185-2193.  doi:10.13287/j.1001-9332.202308.012

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Rising atmospheric carbon dioxide (CO₂) and ozone (O₃) concentrations are the main global change drivers. Soil ectoenzymes play an important role in maintaining soil ecosystem services. Exploring the responses of soil ectoenzymes to elevated CO₂ and O₃ concentrations is important for combating global climate change. In this study, we simulated elevated CO₂ concentrations (+200 μmol·mol^-1, eCO₂), elevated O₃ concentrations (0.04 μmol·mol^-1, eO₃), and their combination (eCO₂+eO₃) in open-top chambers (OTCs), and investigated the responses of rhizospheric soil ectoenzyme activities. The results showed that eCO₂ significantly increased the β-D-Glucosidase (βG) activity by 73.0%, and decreased that of polyphenol oxidase (PHO), peroxidase (PEO), and acid phosphatase (AP) by 48.9%, 46.6% and 72.9% respectively, but did not affect that of cellulose hydrolase (CBH) and β-N-Acetylglucosaminidase (NAG). eO₃ significantly reduced the activities of CBH and AP by 34.2% and 30.4%, respectively. The activities of PHO and AP were reduced by 87.3% and 32.3% under the eCO₂+eO₃ compared with the control, respectively. Results of the principal coordinate analysis, permutation multivariate analysis of variance and redundancy analysis showed that both elevated CO₂ and O₃ significantly affected soil ectoenzyme activities, with stronger effects of elevated CO₂ than elevated O₃. Root nitrogen content, root carbon to nitrogen ratio, soil microbial biomass carbon and nitrate nitrogen were the main drivers of soil ectoenzyme activities under elevated CO₂ and O₃. Elevated O₃ could partially neutralize the effects of elevated CO₂ on soil ectoenzyme activities. In conclusion, elevated CO₂ and O₃ restrained the activities of most soil ectoenzyme, suggesting that climate change would threat soil ecosystem services and functions in the agroecosystem.

Stable isotope compositions and vapor sources of precipitation in the Yellow River Delta, China

TIAN Chao

2023, 34(8):  2194-2204.  doi:10.13287/j.1001-9332.202308.011

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To uncover the vapor source, formation mechanism, and the influence of meteorological factors on precipitation in the saline land of the Yellow River Delta, I employed stable isotopes of precipitation, especially for δ¹⁷O and ¹⁷O-excess, along with the Hybrid Single Particle Lagrangian Integrated Trajectory Model (HYSPLIT), to analyze the isotopic variation characteristics of precipitation and water vapor sources at different temporal scales and precipitation intensities [(<5, 5-10, 10-25, 25-50, >50 mm·d^-1)] from May to October in Dongying, located in the Yellow River Delta. There were wide ranges of isotopes in the daily precipitation data between May and October, with smaller ranges and enriched average values during the dry season. The slope between δ′¹⁸O and δ′¹⁷O was the minimum of 0.5211 when precipitation intensity was below 5 mm·d^-1, indicating the potential influence of evaporation from the moisture source site on precipitation. The maximum value was 0.5268 when precipitation intensity was between 10 mm·d^-1 and 25 mm·d^-1. For precipitation intensities below 50 mm·d^-1 with four different intensities, δ²H, δ¹⁸O and δ¹⁷O decreased with the increase of precipitation. During the dry season, ¹⁷O-excess exhibited a positive relationship with temperature, suggesting the influence of continental circulating water vapor on precipitation. Conversely, in the wet season, ¹⁷O-excess displayed a negative relationship with relative humidity (RH), indicating less influence of evaporation. Analysis of air mass back trajectories using the HYSPLIT model indicated that precipitation during the dry season was primarily influenced by the continental monsoon, while precipitation during the wet season was affected by both oceanic and continental monsoons. In conclusion, precipitation in the Yellow River Delta is influenced by the evaporation of various water vapor sources, local meteorological factors, and atmospheric water vapor sources, resulting in different isotopic signatures across different scales. The fin-dings would provide a scientific basis for the allocation of scarce water resources in the Yellow River Delta.

Silicon composition and stoichiometric ratios with other nutrients in the lower Minjiang River, Southeast China

LIU Jiani, ZHAI Shuijing, QIU Siting, YU Xinhui, WANG Sai

2023, 34(8):  2205-2214.  doi:10.13287/j.1001-9332.202308.028

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Over the past decades, rivers have delivered imbalanced nutrient loads to coastal marine ecosystems due to human activities, which leads to serious regional or global eutrophication problems. The Minjiang River is heavily influenced by human activities. To understand the changing characteristics of nutrient transport ratios in the Minjiang River waters, we measured the seasonal variations of carbon, nitrogen, phosphorus and silicon nutrients in the lower surface waters of the Minjiang River between July 2019 and July 2020. The results showed that the annual average contents of dissolved silicon (DSi), lithogenic silicon (LSi) and biogenic silicon (BSi) in the surface waters of the lower Minjiang River were 5.30, 4.58 and 2.37 mg·L^-1, respectively. There were large seasonal differences among these parameters, with higher content of DSi than LSi and BSi in summer, higher content of DSi than BSi and LSi in autumn and higher content of LSi than DSi and BSi in winter. The proportions of DSi in total silicon tended to decrease gradually from land to sea, while the proportion of BSi was on the contrary. In term of stoichiometric ratios, the Minjiang River mostly presented carbon or phosphorus limitation and was unlimited by silicon or nitrogen. About 1.03×10¹⁰ mol DSi and 0.46 ×10¹⁰ mol BSi were delivered via the Minjiang River to the ocean yearly, showing a decreasing trend year by year. Based on the data in recent years, the nutrient loads of carbon, nitrogen, and phosphorus transported by Minjiang River showed an increasing trend. The imbalanced nutrient loads may lead to changes in the structure and function of the river, estuary, and offshore ecosystems. The study of nutrient stoichiometric ratios can provide a theoretical basis for solving the problems in structural balance of nutrients and eutrophication in Minjiang River estuary and adjacent marine waters.

Spatiotemporal variations of ecosystem security pattern in Horqin sandy dune meadow alternating area, China

MA Kuo, HAO Lina, TONG Xin, DUAN Limin, CAO Wenmei, KANG Xueer, LIU Xiaoyong, LIU Tingxi

2023, 34(8):  2215-2225.  doi:10.13287/j.1001-9332.202308.021

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The natural and geographical environment of ecologically fragile areas in northern China is complex. Due to heavy human disturbance and impacts of climate change, the sustainable development of ecosystems is facing serious challenges. Constructing ecological security pattern can provide decision-making basis for ecological environment protection in desertification areas. Based on land use change data of Horqin dune-meadow interphase area from 1985 to 2021, we identified ecological sources with the importance of ecosystem services and ecological sensitivity, and constructed the ecological security pattern using the minimum cumulative resistance model. We further analyzed the ecological security pattern and its development trend in 1985, 1995, 2005, 2015 and 2021, and explored the ecological spatial layout adjustment strategy. The results showed that the proportion of source area in the ecological security pattern of the study area was always small and scattered from 1985 to 2021, the network of ecological corridors was low, and the connectivity between ecological patches was lacking. The ecological security pattern had experienced a trend of deterioration first and then gradually improving. Ecological policies such as returning farmland to forest and grassland and afforestation had significantly improved the environmental security. We optimized the study area by combining the cultivated land suitability evaluation method. The ecological security pattern showed a spatial trend of ‘dual-core, scattered and semi-surrounded'. The results could provide references for the construction of county-scale ecological security pattern in ecologically fragile areas and the ecological management of Horqin sands.

Construction and planning application of blue-green ecological network in Ruzhou City based on morphological spatial pattern analysis (MSPA)

MAO Yuanyuan, XU Fan, GAO Yixuan, HUANG Kun, LI Xin, HU Hao

2023, 34(8):  2226-2236.  doi:10.13287/j.1001-9332.202308.025

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Land space planning is an important way to realize the construction of ecological civilization. It is important to improve the ecological service capacity of urban blue-green space during land space planning and combine it with planning strategies. With Ruzhou City from Henan Province as the research area, we constructed the current blue-green ecological network by morphological spatial pattern analysis (MSPA), connectivity analysis and minimum cumulative resistance model, and explored the application of corridor construction in land spatial planning. The results showed that there were seven first-level core patches, which were mainly distributed in the mountain forest space in the southwest and northeast of the city and the belt ecological space formed by Ruhe River in the middle. There were nine second-level core patches. A total of 256 ecological corridors and 135 ecological nodes were screened out. Most of the corridors crossed Ruhe River, so we should focus on protecting Ruhe River and its surrounding environment, providing temporary habitat for biological migration from north to south, improving the stability of overall ecological network, and concerning the restoration of the corridor breakpoints on the west and south sides of the city. It could guide the division of urban development boundaries, and provide scientific basis for the functional orientation and classified management and control of corridors from the perspective of planning.

Regionalization and optimization strategy of ecological management in Xinjiang, China based on supply-demand relationship and spatial flow of ecosystem services

XIONG Xinying, MENG Mei

2023, 34(8):  2237-2248.  doi:10.13287/j.1001-9332.202308.023

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As an important basis for the optimization of territorial space, ecological management zoning is of great significance for maintaining regional ecological security and promoting the construction of ecological civilization. With 10 ecosystem services, such as wind break and sand fixation, water conservation, and forest and grass supply, we built a supply index system for Xinjiang. Modelling and ecological economics methods were used to quantify ecosystem service supply. Ecosystem service demand of Xinjiang in 2020 was quantitatively assessed by combining land use intensity, population, and economic status. Based on the ecosystem service supply-demand ratio model and quadrant matching method, we explored the matching relationship and spatial differentiation of ecosystem ser-vice supply and demands on the 1 km grid scale. The breaking point formula and field intensity formula were used to evaluate the flow range and intensity of ecosystem services, and then ecological management zones were divided and corresponding control measures were proposed. The results showed obvious spatial differences in the supply and demand of ecosystem services in Xinjiang in 2020. The high-supply areas were mainly distributed in river valleys and along river systems, while the demand was concentrated in oasis-central cities. The overall supply of ecosystem services was less than the demand. The spatial distribution was dominated by low supply-low demand areas and high supply-high demand areas. There were seven output zones of ecosystem services in Xinjiang, namely Fuyun County, Fuhai County, Yizhou District, Shanshan County, Alashankou City, Keping County and Qira County. The rests were input zones. According to the comprehensive analysis, Xinjiang could be divided into five ecological management areas, i.e., mountain ecological barrier area, oasis ecological restoration area, desert ecological improvement area, desert-oasis ecological protection area, and patch ecological transport area.

Estimation of life history traits and stock status for Scomber japonicus based on data-limited method

ZHOU Yufei, DENG Jiayi, MA Qiuyun, YE Shen

2023, 34(8):  2249-2258.  doi:10.13287/j.1001-9332.202308.029

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The age-structure data is usually unavailable for most traditional fishery species in the East China Sea. The data-limited method is thus particularly important to understand life history and population dynamics of commercial fishes. At the offshore waters of southern Zhejiang, Chub mackerel (Scomber japonicus) is one of the dominant economic species. Based on fork length data from 2016 to 2020, we estimated its life history traits with the data-limited method, including the growth parameters and mortality coefficients. We further evaluated the status of Chub mackerel by the yield per recruitment (YPR) model. The results showed that the relationship between fork length (L) and body weight (W) based on 1606 samples was estimated to be W=4.18×10^-3L^3.28(R²=0.96). The asymptotic fork length L_∞ of Chub mackerel was 28.34 cm, the growth rate was 0.36 a^-1, and the initial theoretical age was -0.40 a. The total mortality was estimated as 1.67 a^-1, and the estimated natural mortality (M) was 0.85 a^-1. The fishing mortality (F) was 0.82 a^-1, and the development rate was 0.49. The current capture age was estimated to be 1.78 a, while the capture fork length was 15.44 cm. The YPR model results showed YPR value showed a trend of increasing and then decreasing with the increases of F. The values of biological reference points F_0.1 and F_max were 0.97 a^-1 and 4.55 a^-1, respectively, which were higher than the value of current F. The sensitivity analysis showed that the uncertainty of M greatly influenced the estimation results of YPR and biological reference points. A decrease in M significantly increased the YPR value, but F_0.1 and F_max decreased. The status of Chub mackerel stock at the offshore waters of southern Zhejiang is in good condition. However, the miniaturization of catch is intensifying. It is recommended to extend the capture fork length to 20 cm (the impact point age) to improve the quality of the catch, which would sustainably use the Chub mackerel resources.

Effects of microcystin on protein profile in hepatopancreas of Litopenaeus vannamei

LIN Jingui, ZHANG Dajuan, JIA Yingxuan, WANG Yanzhao, ZHANG Shulin, BI Xiangdong

2023, 34(8):  2259-2266.  doi:10.13287/j.1001-9332.202308.031

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For intensive aquaculture in freshwater ponds, microcystin (MC-LR) generated from cyanobacterial blooms is one of the bottlenecks for the healthy and sustainable development of shrimp aquaculture industry. In this study, we measured the MC-LR content in the hepatopancreas and muscles of Litopenaeus vannamei stressed by MC-LR, and analyzed protein expression in the hepatopancreas using DIA high-throughput proteomics technology. The results showed that MC-LR content in the hepatopancreas and muscles reached the highest at 1 h after MC-LR injection, which was (6.12±0.45) μg·kg^-1 and (5.00±0.19) μg·kg^-1, respectively. Then, it decreased gra-dually, with that in the hepatopancreas being significantly higher than in muscles. We identified 820 differential expressed proteins, including 586 up-regulated and 234 down-regulated ones. Results of bioinformatics analysis showed that MC-LR stress significantly affected immune-related pathways such as lysosome, RIG-Ⅰ receptor signals and interleukin-2. It also altered energy metabolisms including citrate cycle, metabolism of starch and sucrose, and interconversion of pentose and glucoronate, which in turn led to the disorder of carbohydrate metabolism. In addition, MC-LR significantly upregulated 19 cytoskeleton-related blood shadow proteins and damaged the hepatopancreas cytoskeleton. It was concluded that MC-LR mainly affected the physiological processes associated with immunity, energy metabolism, and cytoskeleton in the hepatopancreas of L. vannamei.

Suitable habitat of Lepidochelys olivacea and the changes under climate change

XING Yankuo, KANG Bin, LU Zhichuang, GAO Xianggang, WANG Zhen, TIAN Jiashen

2023, 34(8):  2267-2273.  doi:10.13287/j.1001-9332.202308.030

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As a vulnerable species identified by the International Union for Conservation of Nature (IUCN), Lepidochelys olivacea has attracted extensive attention in recent years. To examine its current distribution and that under future climate change scenarios, we compiled the occurrence data of L. olivacea. With eight predictor variables, including depth, offshore distance, mean primary productivity, minimum primary productivity, mean sea surface temperature, minimum sea surface temperature, mean sea surface salinity, and minimum sea surface salinity, we predicted its distribution in an ensemble species distribution model. The accuracy of the model was evaluated with the parameters of areas under curves (AUC) and true skill statistics (TSS). The results showed that the AUC and TSS values were 0.96 and 0.81, respectively, indicating a good predictive performance of the ensemble model. Sea surface temperature and salinity were the two most important variables determining the distribution of L. olivacea, with the suitable temperature ranging from 23 to 29 ℃ and salinity below 34. The current distribution range of L. olivacea was between 30° N—25° S. Under future climate scenarios, its distribution range would decrease, especially under the RCP85 scenario in the 2100s (with a 28% reduction in the suitable survival range). The results of model validation showed that it had high accuracy and could make accurate predictions of the distribution. This study would provide references for the development of more rational conservation measures and management strategies.

Reviews

Behavioral and ecotoxicology of sulfonamide metabolites in the aquatic environment

DAI Jiajia, SONG Jinming, LI Xuegang, MA Jun, YUAN Huamao, DUAN Liqin, WEN Lilian, QU Bao-xiao, XING Jianwei, WANG Qidong

2023, 34(8):  2274-2284.  doi:10.13287/j.1001-9332.202308.032

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Sulfonamides (SAs) are the first broad-spectrum synthetic antimicrobial agents used in human health and veterinary medicine. The majority of SAs entering human body is discharged into aquatic environment in the form of parent material or metabolites. The residues of SAs and their metabolites in the aquatic environment and the development of drug resistance can be serious threats to ecosystems and human health. We summarized recent advances in the research of SAs. The main metabolite types of SAs and the distribution characteristics of metabolites in different aquatic environments were introduced. The ecotoxicology of SAs metabolites, especially the distribution and hazards of sulfonamide resistance genes (sul-ARGs), were discussed with emphasis. Finally, the future research works were proposed. This paper could provide basic information for further research on SAs.

Exploring the potential of roof greening for low-carbon landscapes

DONG Xin, LIU Xiao, HE Baojie

2023, 34(8):  2285-2296.  doi:10.13287/j.1001-9332.202308.020

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As one type of urban artificial ecosystems, roof greening exhibits carbon source/sink characteristics during their life cycle. The carbon cycle mechanism is complex. The lack of exhaustive carbon performance quantification methods and assessment indicators hinders the promotion and implementation of green roof urban decarboni-zation. Focusing on the quantification of roof greening low-carbon landscape potential, we analyzed the internal carbon cycle mechanism of green roof systems and explored four carbon reduction and sink pathways (P₁-P₄): biogenic carbon sink, embodied carbon, operational carbon, and bioenergy supply. Based on the dual performance indicators of normalized value of carbon emissions and carbon payback time, we summarized the normalized value measurement method of each pathway. The potential and characteristics of each pathway were quantified by extracting data from the literature. The results showed that the quantified potential values for P₁ to P₄ were 9.54, -2.26, 2.96 and 0.35 kg CO₂·m^-2·a^-1, respectively, and that the potential values for each pathway were strongly influenced by plant types, climate, and other factors. The imperfect base database and the heterogeneity of assessment scenarios impacted the accuracy of the measurements. The integrated low carbon landscape potential of extensive green roofs was discussed in sub-scenarios, with the 40-year-life cycle integrated carbon reduction ranging from 92.24 to 433.42 kg CO₂·m^-2 and the carbon payback period ranging from 5 to 14 years. Finally, we summarized the problems in the assessment to facilitate future updates and improvements.

Virtual ecological technology: Concepts, systems, and application perspectives

XIE Xiao, WU Tingchen, CAO Beilei, LI Jingzhong, XUE Bing

2023, 34(8):  2297-2304.  doi:10.13287/j.1001-9332.202308.022

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Virtual ecological technology is a new technology that builds the foundation of a digital ecological system, simulates the process of ecological evolution, and establishes a global knowledge analysis system based on a unified spatio-temporal benchmark. It is a new direction for the interdisciplinary integration and development of eco-logy, geographic information science, computer science and other subjects towards modernization, informatization, and intelligence. Research, development, and application of virtual ecological technology is of great significance for the development of ecology as a discipline, ecosystem management, and regional sustainable development. Curren-tly, research on virtual ecological technology is still in its infancy and lacks a complete and clearly defined framework, making it difficult to support systematic iterative development and scientific analysis. In this paper, starting from the main theories and objectives of modern ecology, we summarized the main contents and technical requirements of virtual ecological construction, and proposed a key technical system of virtual ecology that integrated vir-tual geography and digital twin technology. From the perspective of application scenarios, we analyzed the application capabilities of virtual ecological technology in air pollution and energy analysis. Finally, we summarized the deve-lopment potential of virtual ecological technology in the digital construction of the ecological environment, intelligent computing, and realistic expression of different levels of ecological space resources transformation under the background of new generation of information technology, both at the local computing point breakthrough and the global technology point fusion aspects. This would enrich and advance the technical capabilities that support China's ecological space resource transformation.