Table of Content

18 May 2011, Volume 22 Issue 05

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Articles

Effects of topographic factors on the distribution patterns of ground plants with different growth forms |in montane forests in North Guangdong, China.

2011, 22(05):  1107-1113. 

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By using canonical correspondence analysis (CCA), this paper studied the effects of small-scale topographic changes on the distribution patterns of ground plants with different growth forms in the montane evergreen broad-leaved forest in Chebaling National Nature Reserve of North Guangdong, China. It was observed that slope aspect, slope grade, and slope position had significantly integrative effects on the distribution patterns of four growth form ground plants (fern, liana, herb, and shrub). Slope aspect had significant effects on the distribution patterns of all four ground plants but slope position didn’t have, whereas slope grade only affected the distribution pattern of shrub significantly. From shady slope to semi-shady slope, and  to semi-sunny slope, the abundance of the four growth form ground plants decreased gradually, indicating that shade plants were dominant in the ground vegetation of subtropical montane evergreen broad-leaved forest. Most shrubs were shade-tolerant species, and their change patterns of richness and diversity with slope aspect were the same as the change pattern of abundance. Shrubs were sensitive to the change of slope grade, and richer on gentle slopes. In hilly and low mountains, slope position changed little, and had less effects on the distribution patterns of ground plants. At stand-level, horizontal topographic factor (slope grade aspect) had much greater effects on the distribution patterns of ground plants, as compared with vertical topographic factors (slope grade and slope position), which suggested that slope aspect was the major factor affecting the water and heat conditions in subtropical montane forest.

Effects of highway |on the vegetation species composition along a distance gradient from road edge in southeastern margin of Tengeer Desert.

2011, 22(05):  1114-1120. 

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Aimed to examine the effects of highway  on the vegetation species composition in arid desert area, forty-eight transects perpendicular to the  provincial highway 201 from Shapotou to Jingtai in the southeastern margin of Tengger Desert were installed, with the vegetation species distribution along a distance gradient from the road edge investigated. The results showed that with increasing distance from the road edge, the species number, coverage, biomass, and α-diversity of herbaceous plants declined, but had no significant differences with the control beyond 5 m. Within 0-6 m to the road edge, the herbaceous plant height was greater than that of the control, but their density had less change. Within 0-2 m to the road edge, the species turnover rate of herbaceous plants was lower; at 2-5 m, this rate was the highest; while beyond 10 m, the species composition of herbaceous plants was similar to that of the control. The herbaceous plant community at the road edge was dominated by gramineous plants, with the disturbance-tolerant species Pennisetum centrasiaticum, Chloris virgata, and Agropyron cristatum accounting for 68.6% of the total. C. virgata beyond 1 m to the road edge had a rapid decrease in its individual number and presence frequency,  P. centrasiaticum and A. cristatum beyond 2 m also showed a similar trend, while the composite plants Artemisia capillaris and A. frigida beyond 2 m from the road edge had a rapid increase in its individual number, accounting for 70% of the herbaceous plants. At the road edge, the coverage and density of shrubs were significantly lower than those of the control, but the species composition had no significant difference.

Structural characteristics of Sophora moorcroftiana community on wind-sandy land in middle reaches of Yaluzangbu River.

2011, 22(05):  1121-1126. 

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Based on quadrat investigation and hierarchical cluster analysis, this paper studied the structural characteristics of Sophora moorcroftiana community at its different restoration succession stages on the wind-sandy land in middle reaches of Yaluzangbu River. The plant community on the wind-sandy land could be divided into 6 types, i.e., S. moorcroftiana community, Orinus thoroldii community, S. moorcroftiana<O. thoroldii community, S. moorcroftiana-O. thoroldii community, Artemisia weiibyii+S. moorcroftiana community, and S. moorcroftiana+A. weiibyii community. The restoration succession began with the sand-fixing S. moorcroftiana distributed on moving dune, followed by O. thoroldii invasion, and then, S. moorcroftiana-O. thoroldii community formed gradually. Another restoration succession approach began with O. thoroldii community, S. moorcroftiana occurred then, and finally, S. moorcroftiana-O. thoroldii community formed. On semi-fixed dune, A. weiibyi could invade the community, and S. moorcroftiana+A. weiibyi community formed. The climax community on the wind-sandy land was the shrub community dominated by S. moorcroftiana. With increasing slope grade, the coverage and height of S. moorcroftiana community tended to decrease. Biological crust had definite improvement effect on the soil physical and chemical properties. At the places with biological crust, surface soil water content was significantly higher, compared with that at the places with other restoration succession stages of S. moorcroftiana community. The crown diameter, plant height, and the sprouting branch number of S. moorcroftiana community were the highest on moving dune, followed by on fixed dune, and on semi-fixed dune. The dead branch number at different restoration succession stages indicated that  S. moorcroftiana population had a declining trend after the sand was fixed.

Effects of extreme drought on plant species in Karst area of Guizhou Province, Southwest China.

2011, 22(05):  1127-1134. 

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Based on the investigation data of damaged vegetations in Karst areas of Guizhou Province during the extreme drought in 2010, an investigation was made on the species composition, floristic composition, life form, leaf characteristics, and environmental conditions of drought-damaged plants at six sampling plots. At these plots, there were 31 plant species drought-damaged, among which, Cunninghamia lanceolata, Celastrus orbiculatus, Rapanea neriifolia, Myrsine semiserrata, Cyclobalanopsis glauca, and Cinnamomum glanduliferum damaged most, and the tropical evergreen arbors with mesophyllous, leathery, and simple leaf suffered more seriously. The damaged plants mainly located on the middle or upper part of steep slopes, and on the thin limestone soils originated from horizontal attitude carbonate rocks. The plants in the microhabitats with soil layer <30 cm and rock-soil were damaged most, accounting for 87.4% and 40.0% of the total, respectively. It was suggested that the temperate deciduous trees with microphyll could be more planted in Karst areas, and  that the microhabitat for the afforestation could be  in gully and with thicker soil layer and good site condition.

Point pattern analysis of Phyllostachys bissetii ramet population in West China Rainy Area.

2011, 22(05):  1135-1140. 

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In this paper, point pattern analysis was conducted to study the spatial distribution of Phyllostachys bissetii ramet population and the spatial association between different age-class P. bissetii ramet populations in West China Rainy Area. The ramet population had a clumped distribution at the scale 0-0.32 m, a regular distribution at the scale 0.64-4.48 m, and a random distribution at the scale >4.48 m. Different age-class ramet populations mainly had a random distribution at the scale 0-8.00 m, though a slight difference was observed among different age-classes. The spatial association between age-classⅠand age-classes Ⅱand Ⅲ at the scale 1.76-4.16 m and 0.32-4.16 m approached to or reached to negative, respectively, while the spatial association between age-classes Ⅰand Ⅳ at the scale 0.32-3.04 m was significantly negative, indicating that the spatial negative association between younger and elder ramet populations increased with enlarged age-class difference.  The spatial pattern of P. bissetii ramet population and the spatial association between different age-class ramet populations were depended on spatial scale, ramet age, and environmental factors.

Cold resistance of Pistacia chinensis and Koelreuteria integrifoliola.

2011, 22(05):  1141-1146. 

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Taking one-year-old dormant shoots of Pistacia chinensis and Koelreuteria integrifoliola as test materials and the shoots of northern indigenous tree species K. paniculata as the control, the changes of their membrane-lipid peroxidation, antioxidative enzyme activity, and organic osmoregulatory substance content under artificial cooling were studied, aimed to analyze the differences of the three tree species in cold resistance. With the decrease of temperature, the ion leakage percentage of the three tree species increased in S-shape, and the SOD and POD activities decreased after an initial increase. The MDA, soluble protein, and soluble sugar contents of K. integrifoliola and K. paniculata under decreasing temperature decreased after an initial increase, while those of P. chinensis had an increasing trend. The semi-lethal temperature (LT₅₀) of K. paniculata, K. integrifoliola, and P. chinensis calculated by the Logistic equation of ion leakage percentage was -27.2 ℃, -23.7 ℃, and -27.0 ℃, respectively. Among the three tree species, K. paniculata had the strongest cold resistance, followed by P. chinensis, and K. integrifoliola.

Effects of short term enhanced UV-B radiation on the PSⅡ photochemical efficiency of alpine plant Saussurea superba.

2011, 22(05):  1147-1154. 

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A simulation experiment of short term supplementation of UV-B was conducted to study the changes of chlorophyll fluorescence coefficients of alpine plant Saussurea superba under three typical weather conditions (sunny, cloudy, and shady) in Qinghai-Tibet Plateau. When the weather changed from sunny to shady, the maximal quantum efficiency of PSⅡ photochemistry (F_v/F_m) after 3 minutes of dark adaptation increased significantly, the actual photochemical efficiency of PSⅡ (Φ_PSⅡ) and photochemical quenching (q_P) also increased, but the non-photochemical quenching (NPQ) decreased, demonstrating that PAR was the main factor affecting the PSⅡ photochemical efficiency of S. superba. After the short term supplementation of UV-B, the F_v/F_m and NPQ under the three typical weather conditions had a slight decrease but the Φ_PSⅡ and q_P had a slight increase, while the photosynthetic gas exchange had less change. The increasing trend of net photosynthetic rate P_n and Φ_PSⅡ under enhanced UV-B radiation could be related to the existence of more UV-A component, and also, benefited from the increased leaf thickness. UV-B radiation had potential negative effects on leaf photosynthetic components.

Effects of NaCl stress on the seedling growth and K⁺- and Na⁺-allocation of four leguminous tree species.

2011, 22(05):  1155-1161. 

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Taking the pot-cultured seedlings of four leguminous tree species (Albizia julibrissin, Robinia pseudoacacia, Sophora japonica, and Gleditsia sinensis) as test materials, this paper studied their growth indices, critical salt concentration (C₅₀), and K⁺ and Na⁺ allocation under different levels of NaCl stress, aimed to understand the difference of test tree species in salt tolerance. NaCl stress inhibited the seedling growth of the tree species. Under NaCl stress, the  dry matter accumulation decreased, while the root/shoot ratio increased, especially for A. julibrissin and G. sinensis. Quadratic regression analysis showed that the C₅₀ of A. julibrissin, R. pseudoacacia, S. japonica, and G. sinensis was 3.0‰, 5.0‰, 4.5‰, and 3.9‰, respectively,i.e., the salt tolerance of the four tree species was in the order of R. pseudoacacia > S. japonica > G. sinensis > A. julibrissin. In the root, stem, and leaf of the four tree species seedlings, the Na⁺ content increased with the increase of NaCl stress, while the K⁺ content (except in the root of A. julibrissin) decreased after an initial increase, resulting in a larger difference in the K⁺/Na⁺ ratio in the organs. Under the same NaCl stress, the allocation of Na⁺ in different organs of the four tree species seedlings decreased in the order of root>stem>leaf, while that of K⁺ differed with tree species and NaCl stress, and leaf was the main storage organ for K⁺. The K⁺/Na⁺ ratio in different organs decreased in the sequence of leaf>stem>root. R. pseudoacacia under NaCl stress accumulated more K⁺ and less Na⁺ in stem and leaf, and had higher K⁺/Na⁺ ratio in all organs and higher dry mass, being assessed to be more salt-tolerant. In contrast, A. julibrissin under high NaCl stress accumulated more Na⁺ in stem and leaf, and had a lower K⁺/Na⁺ ratio in all organs and lower dry mass, being evaluated to be lesser salt-tolerant. The K⁺ accumulation in seedling stem and leaf and the Na⁺ retention in seedling root could be the main reasons for the salt tolerance of leguminous tree species under NaCl stress.

Soil hydrolase characteristics in late soil-thawing period in subalpine/alpine forests of west Sichuan.

2011, 22(05):  1162-1168. 

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Late soil-thawing period is a critical stage connecting winter and growth season. The significant temperature fluctuation at this stage might have strong effects on soil ecological processes. In order to understand the soil biochemical processes at this stage in the subalpine/alpine forests of west Sichuan, soil samples were collected from the representative forests including primary fir forest, fir and birch mixed forest, and secondary fir forest in March 5-April 25, 2009, with the activities of soil invertase, urease, and phosphatase (neutral, acid and alkaline phosphatases) measured. In soil frozen period, the activities of the three enzymes in test forests still kept relatively higher. With the increase of soil temperature, the activities of hydrolases at the early stage of soil-thawing decreased rapidly after a sharp increase, except for neutral phosphatease. Thereafter, there was an increase in the activities of urease and phosphatase. Relative to soil mineral layer, soil organic layer had higher hydrolase activity in late soil-thawing period, and showed more obvious responses to the variation of soil temperature.

Low-phosphorus tolerance and related physiological mechanism of Xieqingzao B//Xieqingzao B/Dongxiang wild rice BC₁F₉ populations.

2011, 22(05):  1169-1174. 

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By the method of water culture, the low-phosphorus tolerance of 221 lines of Xieqingzao B//Xieqingzao B/Dongxiang wild rice BC₁F₉ populations was indentified. The morphological indices including plant height, leaf age, yellow leaf number, and shoot dry mass as well as the physiological indices including MDA, soluble sugar, and shoot phosphorus content were measured, also, the phosphorus efficiency was calculated, and the correlations among the indices were analyzed. All the 221 lines had differences in the seven test indices, and the low-phosphorus tolerance lines under low-phosphorus stress had higher values of relative leaf age, relative plant height, relative shoot dry mass, and relative soluble sugar content, but lower values of relative yellow leaf number and relative malondialdehyde content. The relative shoot phosphorus content had less difference. Phosphorus efficiency was positively correlated with phosphorus utilization efficiency and phosphorus uptake  efficiency, and the correlation between phosphorus efficiency and phosphorus utilization efficiency was at significant level (P<0.01), suggesting that the low-phosphorus tolerance capability of the low-phosphorus tolerance lines was mainly attributed to the high phosphorus utilization efficiency of the lines, namely, low-phosphorus tolerance lines had stronger capability in synthesizing dry mass with per unit phosphorus uptake.

Effects of sulfur plus resin-coated controlled release urea fertilizer on winter wheat dry matter accumulation and allocation and grain yield.

2011, 22(05):  1175-1182. 

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A field experiment was conducted to study the effects of sulfur plus resin-coated urea fertilizer on the winter wheat dry matter accumulation and allocation and grain yield. Four treatments were installed, i.e., sulfur plus resin-coated urea (SRCU), resin-coated urea (RCU), sulfur-amended conventional urea (SU), and conventional urea (U). The coated urea fertilizers were applied as basal, and the conventional urea fertilizers were 50% applied as basal and 50% applied as topdressing. There were no significant differences in the plant dry matter accumulation and grain yield between treatments RCU and U. Under the conditions the available S content in 0-20 cm soil layer was 43.2 mg·kg^-1 and the S application rate was 91.4 kg·hm^-2, treatments SRCU and SU had no significant differences in the dry matter accumulation and allocation after anthesis and the grain yield, but the amount of the assimilates after anthesis allocated in grain, the grain-filling rate at mid grain-filling stage, the 1000-grain weight, and the grain yield in the two treatments were significantly higher than those in treatment RCU. When the available S content in 0-20 cm soil layer was 105.1 mg·kg^-1 and the S application rate was 120 kg·hm^-2, the grain yield in treatment SRCU was significantly higher than that in treatment SU, but had no significant difference with that in treatments RCU and U. These results suggested that from the viewpoints of dry matter accumulation and allocation and grain yield, the nitrogen released from SRCU had the same regulation effect as the conventional urea 50% applied as basal and 50% applied as topdressing, while the regulation effect of the sulfur released from SRCU was controlled by the available S content in 0-20 cm soil layer. When the soil available S content was 43.2 mg·kg^-1, the released sulfur could promote the dry matter accumulation after anthesis and the grain-filling, and increase the grain yield significantly; when the soil available S content was 105.1 mg·kg^-1 the released sulfur from SRCU had no significant effect in increasing grain yield. Excessive S-amendment could even induce the decrease of grain yield.

Effects of conservation tillage and weed control on soil water and organic carbon contents in winter wheat field.

2011, 22(05):  1183-1188. 

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Taking a long term (since 2004) straw-returning winter wheat field as the object, an investigation was made in the wheat growth seasons of 2008-2009 and 2009-2010 to study the effects of different tillage methods (rotary tillage, harrow tillage, no-tillage, subsoil tillage, and conventional tillage) and weed management on the soil water and organic carbon contents. No matter retaining or removing weeds, the weed density under subsoil tillage and no-tillage was much higher than that under rotary tillage, harrow tillage, and conventional tillage. From the jointing to the milking stage of winter wheat, retaining definite amounts of weeds, no matter which tillage method was adopted, could significantly increase the 0-20 cm soil water content,suggesting the soil water conservation effect of retaining weeds. Retaining weeds only increased the soil organic carbon content in 0-20 cm layer at jointing stage. At heading and milking stages, the soil organic carbon contents in 0-20, 20-40, and 40-60 cm layers were lower under weed retaining than under weed removal. Under the conditions of weed removal, the grain yield under subsoil tillage increased significantly, compared with that under the other four tillage methods. Under the conditions of weed retaining, the grain yield was the highest under rotary tillage, and the lowest under conventional tillage.

Effects of combined fertilization of N, P, and K on nicotine content of filling type flue-cured tobacco.

2011, 22(05):  1189-1194. 

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An orthogonal regression field experiment was conducted to study the effects of combined fertilization of N, P, and K on the nicotine content in the upper leaves of filling type flue-cured tobacco (Nicotiana tobacum) variety “Longjiang 911” from Northeast China. The regression effect models of N, P, and K fertilization rates and upper leaf nicotine content were established, and the effects of the fertilization rates and their interactions were analyzed. Based on these, an optimized NPK fertilization scheme was drawn up to reduce the nicotine content in the upper leaves of “Longjiang 911”. The model analyses showed that the nicotine content in the upper leaves of “Longjiang 911” decreased after an initial increase with the increasing fertilization rate of N, increased with the increasing fertilization rate of P, and had a sharp decrease with the increasing fertilization rate of K. The two-factor effects of NKP on the nicotine content were in the order of NK>PK>NP. Within a certain range of fertilization rates, NP and PK had negative correlations with the nicotine content, suggesting the antagonistic effects between N and P and between P and K, while NK was on the contrary, suggesting the synergistic effects between N and K. A comprehensive analysis on the regression effect models of N, P, and K fertilization rates and upper leaf nicotine content showed that the basal fertilization rates of N, P, and K for the tobacco production on warp soil were recommended as 33.5-47.8 kg·hm^-2, 40.2-63.6 kg·hm^-2, and 78.0-119.6 kg·hm^-2, respectively.

Effects of exogenous CaCl₂ on the functions of flue-cured tobacco seedlings leaf photosystem Ⅱunder drought stress.

2011, 22(05):  1195-1200. 

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Taking  chlorophyll a fluorescence transient OJIP as the probe, this paper studied the effects of foliar spraying 10 mmol·L^-1 of CaCl₂ on the functions of photosystem Ⅱ (PSⅡ) in tobacco seedling leaves under drought stress. Drought stress decreased the conversion efficiency of PSⅡ primary light energy (F_v/F_m) and electron transport rate (ETR), and inhibited the primal process of photosynthesis, resulting in an obvious photoinhibition. After the spraying of CaCl₂, the decrement of quantum yield for electron transport (φE_o) under drought stress was obviously lower, and the increment of electron transport efficiency of per reaction center (ET_o/RC) was obviously higher, compared with those after the spraying of water. Foliar spraying CaCl₂ increased the amount of PSⅡ-captured light energy used for photosynthesis electron transport, the efficiency of surplus active reaction center, as well as the energy transport in electron transport chain, making the PSⅡ remain relatively high activity under drought stress, and accordingly, the drought resistance of the tobacco seedlings was improved.

Estimation model for water requirement of greenhouse tomato under drip irrigation.

2011, 22(05):  1201-1206. 

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Based on the modified Penman-Monteith equation, and through the analysis of the relationships between crop coefficient and cumulative temperature, a new model for estimating the water requirement of greenhouse tomato under drip irrigation was built. The model was validated with the measured data of plant transpiration and soil evaporation in May 2-13 (flowering-fruit-developing stage) and June 9-20 (fruit-maturing stage), 2009. This model was suitable for the estimation of reference evapotranspiration (ET₀) in greenhouse. The crop coefficient of greenhouse tomato was correlated as a quadratic function of cumulative temperature. The mean relative error between measured and estimated values was less than 10%, being able to estimate the water requirement of greenhouse tomato under drip irrigation.

Effects of spent mushroom compost on greenhouse cabbage growth under soil salt stress.

2011, 22(05):  1207-1211. 

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A pot experiment was conducted to study the effect of spent mushroom compost (SMC) in alleviating greenhouse soil secondary salinization and cabbage salt stress. With the amendment of SMC, the salinized soil after 60 day cabbage cultivation had a pH value close to 7.0, its organic matter and available phosphorous contents increased significantly, and the increment of total water-soluble salt content reduced, compared with the control. When the amendment amount of SMC was 10 g·kg^-1, the increment of soil water soluble salt content was the least, suggesting that appropriate amendment with SMC could reduce the salt accumulation in greenhouse soil. Amendment with SMC increased the cabbage seed germination rate, plant height, plant fresh mass, chlorophyll SPAD value, and vitamin C content, and decreased the proline content significantly. All the results indicated that SMC could improve the growth environment of greenhouse cabbage, and effectively alleviate the detrimental effect of salt stress.

Characteristics of soil respiration in Phyllostachys edulis forest in Wanmulin Natural Reserve and related affecting factors.

2011, 22(05):  1212-1218. 

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By using Li-Cor 8100 open soil carbon flux system, the dynamic changes of soil respiration rate in Phyllostachys edulis forest in Wanmulin Natural Reserve in Fujian Province of China were measured from January 2009 to December 2009, with the relationships between the dynamic changes and related affecting factors analyzed. The monthly variation of soil respiration rate in the forest presented a double peak curve, with the peaks appeared in June 2009 (6.83 μmol·m^-2·s^-1) and September 2009 (5.59 μmol·m^-2·s^-1), and the seasonal variation of the soil respiration rate was significant, with the maximum in summer and the minimum in winter. The soil respiration rate had significant correlation with the soil temperature at depth 5 cm (P<0.05), but no significant correlation with soil moisture (P>0.05). The monthly variation of litter fall mass in the forest was in single peak shape, and there was a significantly positive correlation between the monthly litter fall mass and soil respiration rate (P<0.05). Two-factor model of soil temperature and litter fall mass could explain 93.2% variation of the soil respiration rate.

Methane emission flux of Zhalong Phragmites australis wetlands in growth season.

2011, 22(05):  1219-1224. 

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Static chamber/gas chromatogram method was adopted to measure the methane emission flux of Zhalong Phragmites australis wetlands with different water levels in a growth season from May to October, 2009, aimed to understand the methane emission pattern in natural freshwater P. australis wetland in frigid region. During the observation period, the average methane emission flux of test wetlands ranged from -21.18 to 46.15 mg·m^-2·h^-1, with a mean of 7.67mg·m^-2·h^-1. In deep water zone (average water level 100 cm) and shallow water zone (average water level 25 cm), the average methane emission flux was 5.81 and 9.52mg·m^-2·h^-1, with a peak in August and July, respectively, and the minimum in October. In summer (from June to July), the methane emission flux in deep water zone was significantly lower than that in shallow water zone; while in spring (May) and autumn (from August to October), a reversed trend was observed. The methane emission flux had a seasonal pattern of summer > autumn > spring, and a diurnal pattern of being the highest at 12:00 and 14:00 and the lowest at 0:00. Temperature and water level were the major factors affecting the methane emission flux in freshwater P. australis wetlands in frigid region.

Main interspecific competition and land productivity of fruit-crop intercropping in Loess Region of West Shanxi.

2011, 22(05):  1225-1232. 

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Taking the four typical fruit-crop intercropping models, i.e., walnut-peanut, walnut-soybean, apple-peanut, and apple-soybean, in the Loess Region of western Shanxi Province as the objects, this paper analyzed the crop (peanut and soybean) photosynthetic active radiation (PAR), net photosynthetic rate (P_n), yield, and soil moisture content. Comparing with crop monoculture, fruit-crop intercropping decreased the crop PAR and P_n. The smaller the distance from tree rows, the smaller the crop PAR and P_n. There was a significantly positive correlation between the P_n and crop yield, suggesting that illumination was one of the key factors affecting crop yield. From the whole trend, the 0-100 cm soil moisture content had no significant differences between walnut-crop intercropping systems and corresponding monoculture cropping systems, but had significant differences between apple-crop intercropping systems and corresponding monoculture cropping systems, indicating that the competition for soil moisture was more intense in apple-crop intercropping systems than in walnut-crop intercropping systems. Comparing with monoculture, fruit-crop intercropping increased the land use efficiency and economic benefit averagely by 70% and 14%, respectively, and walnut-crop intercropping was much better than apple-crop intercropping. To increase the crop yield in fruit-crop intercropping systems, the following strategies should be taken: strengthening the management of irrigation and fertilization, increasing the distances or setting root barriers between crop and tree rows, regularly and properly pruning, and planting shade-tolerant crops in intercropping.

Physiological mechanisms of growth regulators 6-BA and ABA in mitigating low temperature stress of cotton fiber development.

2011, 22(05):  1233-1239. 

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A field trial with high fiber quality cotton cultivar Kemian 1 was conducted in Nanjing (lower reaches of Yangtze Rive) in 2006-2007 to study the effects of growth regulators 6-BA and ABA on the boll and fiber development and related physiological mechanisms under low temperature stress. The cotton seeds were sown on April 25 and May 25, respectively, which could result in different temperature for the bolls on the same positions, and the growth regulators were sprayed at flowering stage. Spraying 6-BA increased the boll weight and fiber quality under both normal and low temperature conditions; whereas spraying ABA induced the decrease of fiber quality under normal temperature but decreased the reduction magnitude of fiber quality under low temperature condition. 6-BA increased significantly the boll sucrose content and sucrose synthase and sucrose phosphate synthase activities, while ABA only increased boll β-1,3-glucanase activity. Both 6-BA and ABA had less effects on the activity of sucrose invertase, a key enzyme for fiber development. Under low temperature condition, spraying 6-BA or ABA improved fiber quality, but the action mechanisms were different. 6-BA improved fiber quality via enhancing the activities of relevant enzymes; while ABA improved fiber quality via increasing the stress resistance of cotton plants.

Dynamics of forest fire weather indices in Tahe County of Great Xing’an Mountains region, Heilongjiang Province.

2011, 22(05):  1240-1246. 

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Based on the 1974-2008 forest fire and meteorological data in Tahe County of Great Xing’an Mountains region, and with the help of Canadian Forest Fire Weather Index System (CFFWIS), this paper qualitatively and quantitatively analyzed the dynamics of forest fire weather indices in the region. In 1974-2008, the mean annual fire occurrence in the region showed an increasing trend, and the increment in 2000-2008 was 72.2%, compared with that in 1974-1999. The fuel moisture codes, fire behavior indices, and fire severity indices in 1974-2008 had an overall increasing trend, which was more evident with time extended. In the future, the probability of forest fire occurrence in the region would be increasing, fuels would be getting drier, fire intensity would be increased, fire weather would be more serious, and fire control would be more difficult. Therefore, more efforts should be made to improve the capability of forest fire control, especially in summer. As a fundamental technique, prescribed burning should be applied to reduce the fuel load. From this doing, the probability of fire occurrence and the fire potential intensity could be reduced.

Changes of China agricultural climate resources under the background of climate change. Ⅴ. Change characteristics of agricultural climate resources in Ningxia.

2011, 22(05):  1247-1254. 

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Based on the 1961-2009 weather data from 21 meteorological stations in Ningxia, this paper analyzed the spatiotemporal variation trend of regional agricultural climate resources in Ningxia, Northwest China. In 1961-2009, the air temperature in Ningxia increased gradually from south to north, with the mean annual temperature increased by 0.4 ℃·(10 a)^-1, while the annual precipitation in most regions decreased gradually, with a decrement  4.26 mm·(10 a)^-1. Both the frost-free period and the duration of crop growth season prolonged. The regions with ≥10 ℃ accumulated temperature being ≥3200 ℃·d extended southwardly, and thereby, the regions adaptive for planting mid and late rice increased. In 2001-2009, most regions were adaptive for plating winter wheat, and the whole Ningxia was adaptive for plating spring wheat. In the southern mountain regions, the region with mean temperature in July being ≤20 ℃ decreased gradually, and accordingly, the regions adaptive for planting potato decreased.

Relationships between urban green belt structure and |temperature-humidity effect.

2011, 22(05):  1255-1260. 

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Taking four green belts with different internal constitutions and  five green belts with different canopy densities along the west fourth ring road of Beijing as test objects, and by using small-scale quantitative measurement method, this paper studied the relationships between different structure urban green belts (width 42 m) and temperature-humidity effect in Beijing. Comparing with the control, lawn had no obvious effect on the decrease of air temperature and the increase of relative humidity, while shrub-herbage, tree-shrub-herbage, and tree-herbage had significant effect. When the canopy density was 10%-31%, green belts had definite effect on the decrease of air temperature and the increase of relative humidity; when the canopy density reached 44%, the effect became significant; and when the canopy density exceeded 67%, the effect was significant and stable.

Regulation effects of reverse-slope level terrace on the runoff and sediment yield in sloping farmland.

2011, 22(05):  1261-1267. 

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A dynamic monitoring on the rainfall-runoff process and the surface runoff and sediment yield in a sloping farmland was conducted at a natural rainfall runoff plot in the watershed of Jianshan River, the first tributary of Fuxian Lake, Chengjiang, aimed to study the regulation effects of reverse-slope level terrace on the runoff and sediment yield in red soil sloping farmlands of Yunnan. The regulation rates of runoff and sediment yield by the reverse-slope level terrace were 49.5%-87.7% and 56.7%-96.1%, averagely 65.3% and 80.7%, respectively, showing that the regulation effects of reverse-slope level terrace on the runoff and sediment yield, especially the latter in sloping farmland were prominent. The variation coefficients of the test parameters for undisturbed sloping farmland and reverse-slope level terrace were in the order of sediment yield > runoff > rainfall. Comparing with undisturbed sloping farmland, reverse-slope level terrace had smaller surface runoff and smaller relative deviation degree of sediment yield, demonstrating its remarkable effect in controlling runoff and sediment yield in sloping farmland.

Regional land main-function division of Guangdong Province based on gravity center and central place theory.

2011, 22(05):  1268-1274. 

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In this paper, the regional land main-function division of Guangdong Province was studied, based on the statistical indices of 21 cities in the Province in 2008 and the central place theory, and by the methods of spatial gravity center and fuzzy clustering. In 2008, cities Guangzhou, Shenzhen, Shantou, Foshan, Dongguan, and Chaozhou were the prior developed zones, lying in gravity center region and well exerted their radiating role in developed economy, being the central region for the development of economy in the Province. Cities Heyuan, Shanwei, Jiangmen, Yangjiang, Zhanjiang, Maoming, and Zhaoqing were the restrictively developed zones. These cities had lower centrality index and worse economic base, and thereby, their ecological restoration and protection should be strengthened to make these cities be established into an eco-benefit ensured region. Cities Zhuhai, Shaoguan, Meizhou, Huizhou, Zhongshan, Qingyuan, Jieyang and Yunfu were the key developed zones, which should undertake the transfer of the industries from prior developed zones of Guangdong and limit the transfer of population from restrictively developed zones of the Province, gradually becoming the main supporting region for the economic development and population agglomeration of Guangdong.

Niche comparison of dominant entomopathogenic fungi in three |forest ecosystems.

2011, 22(05):  1275-1279. 

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An investigation was made on the quantitative composition, niche width, and niche overlap of dominant entomopathogenic fungi in three different forest ecosystems, i.e., natural broad-leaved forest, natural secondary broad-leaved forest, and pure Masson’s pine plantation. In the three forest ecosystems, Beauveria bassiana was the first dominant species in natural secondary broad-leaved forest, the second in pure Masson’s pine plantation, and the third in natural broad-leaved forest. B. bassiana had the broadest temporal niche width and nutritional niche width, whereas the dominant species Isaria cateinannulata, I. farinose, and I. tenuipes had much smaller niche widths. Meanwhile, B. bassiana had larger temporal niche overlaps but smaller nutritional niche overlaps with other dominant entomopathogenic fungi. It was suggested that in the  three forest ecosystems, B. bassiana had the longest occurrence duration, widest host range, and strongest environmental adaptability.

Biodegradation of o-chlorophenol by photosynthetic bacteria under co-metabolism.

2011, 22(05):  1280-1286. 

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Photosynthetic bacterial strain PSB-1D cannot utilize o-chlorophenol (2-CP) as the sole carbon source for energy. In this paper, different carbon sources (malic acid, sodium propionate, sodium acetate, sodium citrate, phenol, glucose, and soluble starch) were taken as the co-metabolism substrates to study their effects on PSB-1D growth and 2-CP degradation under the condition of aerobic culture in darkness. Among the substrates, glucose was most efficient, which promoted the reproduction of PSB-1D,enhanced the 2-CP degradation efficiency, and shortened the degradation period. The optimization experiment of added concentration of glucose showed that when the added glucose concentration was 3g·L^-1, the PSB-1D cell concentration ΔD₅₆₀ after 168 h culture was 1.749, the half-time of 2-CP was shortened to 3.9 d, and the degradation rate constant was increased to 0.00864 h^-1. The SDS-PAGE analysis on the total microbial cellular protein showed that taking glucose as the co-metabolism substrate, PSB-1D could induce a specific 2-CP-degrading enzyme.

Effects of temperature on Keratella quadrata life table demography and morphometric characteristics.

2011, 22(05):  1287-1294. 

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By the method of individual culture, this paper studied the effects of temperature (10 ℃, 15 ℃, 20 ℃, and 25 ℃) on the life table demography (net reproductive rate, intrinsic rate of population increase, generation time, average lifespan, and proportion of mictic offspring) and the offspring morphometric characteristics (body length, body width, antero-median spine length, left and right antero-lateral spine lengths, left and right posterior-spine lengths, and posterior spine number) of two posterior-spined, single posterior-spined, and zero posterior-spined morphotypes of Keratella quadrata. All the test life table demographic parameters and offspring morphometric parameters differed with morphotype and temperature, and their responses to elevated temperature differed with morphotype. Temperature had significant effects on the intrinsic rate of population increase, generation time, average lifespan, and the offspring morphometric parameters (P<0.05); morphotype had significant effects on the offspring body length, antero-median spine length, and left and right posterior-spine lengths (P<0.05) but less effects on the life table demography (P<0.05); and the interaction of temperature and morphotype had significant effects on the generation time and all the offspring morphometric parameters (P<0.05). Among the three morphotypes, the two posterior-spined morphotype had shorter offspring body length (122.1±0.6 μm) than the zero and single posterior-spined morphotypes (126.3±0.7 μm and 125.1±0.7 μm, respectively). The offspring antero-median spine length (32.5±0.3 μm) of the two posterior-spined
morphotype was longer than that of the zero and single posterior-spined morphotypes (31.1±0.3 μm and 30.8±0.3 μm, respectively). The offspring left and right posterior-spine lengths of the two posterior-spined morphotype (31.2±1.0μm and 32.3±0.9μm, respectivedy) were similar to those of the single posterior-spined morphotype（29.5±0.8 μm and 31.5±0.6 μm, respectively), but shorter than those of the zero posterior-spined morphotype (36.7±1.5 μm and 37.3±1.6 μm, respectively). The relationships between the offspring spine length, body width, and body length were also affected by temperature and morphotype.

Dynamics of soil arthropod community structure and its responses to forest fragmentation during the decomposition of Castanopsis eyrei leaf litter.

2011, 22(05):  1295-1301. 

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Five evergreen broad-leaved forests (one continuous forest and four fragmented forests) in the mountain areas in the juncture of Zhejiang, Fujian, and Jiangxi Provinces, East China were selected as test objects to study the dynamics of soil arthropod community structure and its responses to forest fragmentation during the decomposition of dominant tree species Castanopsis eyrei leaf litter. A total of 899  soil arthropods were collected, belonging to 9 classes and 25 orders. Lepidoptera was the dominant taxon, accounting for 10% of the individual, while Hymenoptera, Collembola, Diptera, Prostigmata, and Geophilomorpha were the common taxa. The decomposition rate of C. eyrei leaf litter was the highest in August and lower in April-June and December, which was in accordance with the seasonal dynamics of the taxa number and individual number of soil arthropods. Meanwhile, the taxa number, individual number, and species diversity of soil arthropods differed between continuous forest and fragmented forests, suggesting that both area effect and edge effect affected the dynamics of soil arthropod community structure during the decomposition of C. eyrei leaf litter.

Adult oviposition and larvae feeding behavior of Spodoptera litura (Lepidoptera: Noctuidae) on tobacco plants after infested by B-biotype Bemisia tabaci (Homoptera: Aleyrodidae).

2011, 22(05):  1302-1308. 

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To understand the effects of the defense responses of tobacco plants induced by the infesting of B-biotype Bemisia tabaci to Spodoptera litura, and to
 explore the mechanisms of the interspecific interactions between B-biotype B. tabaci and S. litura, a laboratory experiment was conducted to study the
 effects of tobacco plants after infested by B-biotype B. tabaci on the adult oviposition selection and the larvae feeding, anti-feeding, and other feeding behaviors of S. litura. Comparing with that on control plants, the egg number oviposited by adult S. litura on the infested plants decreased by 40.9%. The plant leaves infested had great repellent effect to the newly-hatched S. litura larvae, while the middle leaves and the leaves with systemic damage symptom (white-vein) had definite attractive effect. Unexpanded terminal leaves had no effects on the host selection of S. litura larvae. The S. litura larvae had significant anti-feeding behavior on the leaves infested, being more notable than that on the leaves with white-vein. On the leaves infested and with white-vein, the feeding times per unit duration or the feeding percentage of S. litura larvae decreased, the time of initiating feeding prolonged, and the total feeding area declined significantly, compared with the control. In conclusion, the tobacco plants after infested by B-biotype B. tabaci had negative effects on the adult oviposition and larvae feeding of S. litura, and the results of the study would be useful in understanding the population dynamics of tobacco pests and their management.

Annual change of phytoplankton ecological features in Fangchenggang Bay of Guangxi, South China.

2011, 22(05):  1309-1315. 

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In March, June, September, and December 2007, investigations were conducted on the species composition, dominant species, community structure, and abundance distribution of phytoplankton in the Fangchenggang Bay of Guangxi. Based on the investigation data, the phytoplankton abundance, biotic index, and their correlations with environmental factors were analyzed. A total of 138 species of 54 genera were identified, among which, 112 species belonged to 37 genera of diatoms, 21 species belonged to 12 genera of dinoflagellates, 2 species belonged to chrysophyta, 2 species belonged to chlorophyta, and 1 species belonged to cyanophyta. In whole year, the dominant species was Skeletonema costatum.The species number had a trend decreasing from the outer to the inner of the Bay and from spring to winter, while the cell abundance was decreased from the inner to the outer of the Bay. There was an obvious annual change in the cell abundance, being the highest (151.39×10⁴ cells·dm^-3) in summer (June) and the lowest (0.35×10⁴ cells·dm^-3) in winter (December). In spring, both the diversity and the species number were higher. Correlation analysis demonstrated that the distribution of phytoplankton community had definite correlations with water nutrient content, temperature and salinity. At the observation stations 1 and 2 in west Bay, due to the effects of Fangcheng River runoff and hydrodynamic forces such as tide, water salinity was lower and nutrient content was higher, and accordingly, S. costatum cells in summer could greatly reproduce, even result in high probability of red tide.

Spatial distribution patterns of heterotrophic, nitrogen, and phosphate bacteria in hypoxic zone of Yangtze River Estuary.

2011, 22(05):  1316-1324. 

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In August 15-28, 2009, a preliminary study was conducted on the spatial distribution characteristics of heterotrophic bacteria (HB), inorganic phosphate bacteria (IPB), organic phosphate bacteria (OPB), denitrifying bacteria (DB), and ammonifying bacteria (AB) in the hypoxic zone of Yangtze River Estuary. In the water surface, water bottom, and sediment surface of the zone, the average quantity of AB was the largest, being 307.52×10⁴ cells·L^-1, 184.50×10⁴ cells·L^-1, 199.97×10² cells·g^-1, followed by that of HB (87.35×10⁴  cfu·L^-1, 86.85×10⁴ cfu·L^-1, and 19.56×10² cfu·g^-1), and of OPB (19.26×10⁴  cfu·L^-1, 18.82×10⁴ cfu·L^-1, and 19.56×10² cfu·g^-1, respectively). IPB was only observed within the Yangtze Estuary, south passage of the Estuary, and Zhoushan inshore, and its average quantity in the water surface, water bottom, and sediment surface was 18.50×10⁴  cfu·L^-1, 31.00×10⁴  cfu·L^-1, and 7.17×10² cfu·g^-1 respectively. DB had a wide distribution, but its average quantity was low, being 3.94×10⁴ cells·L^-1, 23.08×10⁴  cells·L^-1, and 6.22×10² cells·g^-1 in the water surface, water bottom, and sediment surface, respectively. Salinity, NO₃^--N, PO₄^3--P, SiO₃²-Si, and pH were the main factors affecting the distribution of HB, IPB, OPB, and DB in water body and sediment surface. The HB, IPB, and OPB in water bottom and sediment surface had significant positive correlation with water temperature; the HB and OPB in water bottom and the IPB in sediment surface were significantly positively correlated with dissolved oxygen (DO); while the AB in sediment surface was significantly negatively correlated with DO. Cluster analysis showed that hypoxia affected the bacterial community structure in sediment surface.

Ecological characteristics of different Pseudosciaena crocea culture models.

2011, 22(05):  1325-1331. 

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A comparative study was conducted on the ecological characteristics of different Pseudosciaena crocea culture models including monoculture P. crocea (F) and polyculture P. crocea with seaweed Gracilaria lichevoides (FG), benthos Perinereis aibuhitensis (FP), and G. lichevoides plus P. aibuhitensis (FGP) in land-based enclosures, with the sediment and water environment condition, culture benefit, and nitrogen (N) and phosphorus (P) reclaim efficiency analyzed. G. lichevoides could effectively remove the N and P in the water body. The water N and P concentrations in FG and FGP were significantly lower than those in F and FP, and the P utilization efficiency reached 33.8%-34.0% of the total P input. P. aibuhitensis improved sediment environment condition. The sediment N and P concentrations in FP and FGP were lower than those in F and FG, and had significant differences between surface sediment (1-2 cm) and subsurface sediment (2-4 cm). Comparing with those in F, the total N, total P, and inorganic P in FP and FGP reduced by 8.9%-9.2%, 6.1%-6.3% and 8.0%-8.1%, respectively. P. aibuhitensis had a higher efficiency in reclaiming sediment P (7.5%-7.8% of the total P input), being able to effectively mitigate the P accumulation in sediment. Among the test models, FGP had the best material utilization efficiency and optimal resource benefit.

Fish community structure and its seasonal change in subtidal sandy beach habitat off southern Gouqi Island.

2011, 22(05):  1332-1342. 

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To understand the characteristics of fish community structure in sandy beach habitats of island reef water areas, and to evaluate the potential capacity of these habitats in local fish stock maintenance, fishes were monthly collected with multi-mesh trammel nets in 2009 from the subtidal sandy beach habitat off southern Gouqi Island, taking the adjacent rocky reef habitat as the control. α and β species diversity indices, index of relative importance (IRI), relative catch rate, and dominance curve for abundance and biomass (ABC curve) were adopted to compare the fish species composition, diversity, and community pattern between the two habitats, and multivariate statistical analyses such as non-metric multidimensional scaling (nMDS) and cluster were conducted to discuss the fish assemblage patterns. A total of 63 fish species belonging to 11 orders, 38 families, and 56 genera were collected, of which, 46 fish species were appeared in the two habitats. Due to the appearance of more warm water species in sandy bottom, the fishes in subtidal sandy beach habitat showed much higher richness, and the abundance catch rate (ACR) from May to July was higher than that in rocky reef habitat. In most rest months, the ACR in subtidal sandy beach habitat also showed the similar trend. However, the species richness and diversity in spring and summer were significantly lower in subtidal sandy beach habitat than in rocky reef habitat, because of the high species dominance and low evenness in the sandy beach habitat. Japanese tonguefish (Paraplagusia japonica) was the indicator species in the sandy beach habitat, and dominated in early spring, later summer, autumn, and winter when the fishing pressure was not strong. In sandy bottom, a unique community structure was formed and kept in dynamic, due to the nursery use of sandy beach by Japanese anchovy (Engraulis japonicus) from May to July, the gathering of gray mullet (Mugil cephalus) in most months for feeding, and the large quantity appearance of plotosid catfish (Plotosus anguillaris) in early Autumn, which was quite different from the community structure pattern dominated by reef fishes in rocky-algae habitat. The subtidal sandy bottom off Gouqi Island was serving as both nursery and feeding grounds for many fish species, being a suitable habitat for flatfishes. It was concluded that the sandy beaches around Gouqi Island could be a very important habitat for economic fish species, especially as a nursery ground for juvenile fishes, contributing to the fish stock maintenance in specific area.

Soil seed bank research of China mining areas: Necessity and challenges.

2011, 22(05):  1343-1350. 

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Soil seed bank consists of all living seeds existed in soil and its surface litter, especially in topsoil, and can reflect the characteristics of regional biodiversity. As the base of vegetation restoration and potential greening material, topsoil and its seed bank are the limited and non-renewable resources in mining areas. The study of soil seed bank has become one of the hotspots in the research field of vegetation restoration and land reclamation in China mining areas. Owing to the special characteristics of mining industry, the soil seed bank study of mining areas should not only concern with the seed species, quantities, and their relations with ground surface vegetation, but also make use of the research results on the soil seed bank of other fragile habitats. Besides, a breakthrough should be sought in the thinking ways and research approach. This paper analyzed the particularity of mining area’s soil seek bank research, summarized the research progress in the soil seed bank of mining areas and other fragile habitats, and put forward the challenges we are facing with. It was expected that this paper could help to reinforce the soil seed bank research of China mining areas, and provide scientific guidelines for taking great advantage of the significant roles of soil seed bank in land reclamation and vegetation restoration in the future.

Fractal theory and its application in the analysis of soil spatial variability: A review.

2011, 22(05):  1351-1358. 

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Soil has spatial variability in its attributes. The analysis of soil spatial variability is of significance for soil management. This paper summarized the fractal theory and its application in spatial analysis of soil variability, with the focus on the utilization of moment method in calculating the fractal dimension of soil attributes, the multi-fractal analysis of soil spatial variability, and the scaling up of soil attributes based on multi-fractal parameters. The  studies on the application of fractal theory and multi-fractal method in the analysis of soil spatial variability were also reviewed. Fractal theory could be an important tool in quantifying the spatial variability and scaling up of soil attributes.

Impacts of hydroelectric cascade exploitation on river ecosystem and landscape: A review.

2011, 22(05):  1359-1367. 

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Hydroelectric cascade exploitation, one of the major ways for exploiting water resources and developing hydropower, not only satisfies the needs of various national economic sectors, but also promotes the socio-economic sustainable development of river basin. However, it exerts unavoidable anthropogenic impacts on the entire basin ecosystem. Based on the process of hydroelectric cascade exploitation and the ecological characteristics of river basins, this paper reviewed the major impacts of hydroelectric cascade exploitation on dam-area ecosystems, river reservoirs microclimate,riparian ecosystems, river aquatic ecosystems, wetlands, and river landscapes. Some prospects for future research were offered, e.g., strengthening the research of chain reactions and cumulative effects of ecological factors affected by hydroelectric cascade exploitation, intensifying the study of positive and negative ecological effects under the dam networks and their joint operations, and improving the research of successional development and stability of basin ecosystems at different temporal and spatial scales.

Allelopathy of garlic root exudates.

2011, 22(05):  1368-1372. 

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By the method of water culture, the root exudates of Cangshan garlic and Caijiapo garlic were collected to study their allelopathic effects on the seed germination and seedling growth of lettuce, and on the development of pathogens Fusarium oxysporum f. sp. cucumerinum and F. oxysporium f.sp. niveum. The root exudates of the two garlic cultivars promoted the lettuce seed germination and seedling growth at low concentrations (0.1 and 0.2 g·mL^-1), but showed inhibitory effects at high concentrations (0.4 and 0.6 g·mL^-1), with the inhibitory effects being stronger for the root exudates of Caijiapo garlic. The two garlic cultivars’ root exudates also had inhibitory effects on the mycelia growth and spore germination of the pathogens, and the effects increased with increasing concentration of the exudates, being stronger for Caijiapo garlic than for Cangshan garlic. F. oxysporum f. sp. cucumerinum was more sensitive to the inhibitory effects of the root exudates of the two garlic cultivars, as compared to F. oxysporium f.sp. niveum.

Allelopathic interactions between invasive plant Solidago canadensis and native plant Phragmites australis.

2011, 22(05):  1373-1380. 

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Taking the seeds of invasive plant Solidago canadensis and native plant Phramites australis from their mono- and co-dominant communities as allelopathic acceptors, this paper analyzed the differences in the seed germination rate and sprout length after treated with five level (12.5, 25, 50, 100, and 200 mg·mL^-1) S. canadensis and P. australis extracts, aimed to understand the allelopathic interactions between the two species. The 1000-grain weight and seed germination rate under distilled water treatment of the two species in co-dominated community were greater than those in mono-dominant community. Low level (12.5 and 25 mg·mL^-1) S. canadensi extracts slightly promoted the seed germination rates of S. canadensis in both mono- and co-dominant communities, but high level (50, 100, and 200 mg·mL^-1) S. canadensi extracts had strong inhibition effect, especially for the S. canadensis in co-dominated community. No significant patterns were observed about the effects of P. australis extract on S. canadensis seed germination. The sprout length of S. canadensis seeds in both mono- and co-dominant communities decreased with increasing level of S. canadensis extract, but decreased in a fluctuation way with increasing level of P. australis extract. After treated with the extracts of P. australis or S. canadensis, the seed germination rate of P. australis in mono-dominant community was significantly greater than that in co-dominant community (P<0.05), but there was no significant difference between these two extracts.