查看更多>>摘要：In order to identify the potential of sulfur (S)content in the rings of Masson pine (Pinus massoniana) in the Pearl River Delta as a bio-indicator of regional history of atmospheric pollution, dendrochemistry was used to determine the temporal distribution of S content in the xylem of Masson pines from Zhaoqing Dinghushan and Nanhai Xiqiaoshan, Guangdong Province, southern China.The results indicated that contents of xylem S increased temporally and peaked in the rings formed in the most recent years at both sites. In the rings tbrmed during the same period before the 1980s, S contents were not signif-icantly different between the two sites, while in the rings formed at the same period after the 1980s, S content at Xiqiaoshan were significantly higher than those at Din-ghushan. The chronosequences of the S indices at both sites could be easily marked as three periods: before 1970,during 1971-1985, and during 1986-2002. Based on the temporal changes of the xylem S contents and certain social-economic indices after the 1980s in the Delta, the history of atmospheric pollution at the study sites could be reconstructed as follows: 1) before 1970, a period in which the air was relatively clear, 2) 1971-1985, a period in which the air was gradually polluted, and 3) 1986-2002, a period in which the air was most severely polluted in the Delta.
查看更多>>摘要：From August 2004 to August 2005, three replicate experimental platforms were constructed in a section of the tidal flats in Yingluo Bay, Guangxi Province to study the growth and physiological responses of Rhizophora stylosa Griff seedlings to tidal waterlogging stress in a diurnal tidal zone. A total of eight tidal flat elevation (TFE) treatments, i.e., 320, 330, 340, 350, 360,370, 380 and 390 cm above Yellow Sea Datum (YSD),were created on each platform. The results showed that lower TFEs (320-330cm YSD) slightly increased the seedling stem height of 1-year old seedlings, while higher TFEs (> 340 cm YSD) increased the seedling growth significantly. Moderate TFEs (350-370 cm YSD) favored the development of knots. Number of leaves, leaf conservation rate and leaf area per seedling all decreased dramatically with decreasing TFE. Lower TFEs caused large damage to Chl a, but Chl b was less affected. The Chl a/b ratio decreased with decreasing TFE. Prolonged waterlogging induced higher SOD activity in roots, while moderate TFE inhibited the SOD activity in leaves. The POD activity in roots and leaves increased with decreasing TFE. Waterlogging stress decreased the biomass of individual organs and entire seedlings. With increasing waterlogging, the biomass partitioning in 1-year old seedlings increased from leaf to stem. The survival rate decreased sharply from 88.9% to 40.0% as TFE decreased,while more than 80% of the seedlings were able to survive at the TFE level of 370 cm YSD and above. We propose that the local mean sea level should be adopted as the critical tidal level for forestation with hypocotyls of R.stylosa along the Guangxi coast.
查看更多>>摘要：Euryodendron excelsum H. T. Chang is an endangered species of the family Theaceae endemic to China. It is listed as a second-class endangered plant for state protection in the Red Data Book of Plants in the People's Republic of China. The species is restricted to one remnant population with less than 200 individuals in the Bajia region of Yangchun County, Guangdong Province.This study was conducted to determine the status of the population, analyze the past population structure and forecast the future population dynamics of E. excelsum.The size structure and height structure of the population of E. excelsum were tabulated and analyzed. Based on these data, we estimated the values of the parameters such as survival curve, mortality curve and life expectancy.Population dynamics was predicted by a time-sequence model. The size distribution of the whole population generally fit a reverse "J" type curve, suggesting a stable population. The number of young individuals was larger than that of middle-aged and old individuals. The analysis of life table and survival curves show that under environmental screening and human disturbance, the population had one peak of mortality in size class Ⅱ and only 11.43% individuals could survive from size class Ⅱ to size class III. The life expectancy of E. excelsum was the highest in size class IV. The survival curve of the population belongs to the Deevey-III type. Time-sequence models for E. excelsum population predict that the number of different size classes will increase after two and five years. As a result, the crucial factors for the natural regeneration and restoration of E. excelsum are the protection of living individuals and their habitat.
查看更多>>摘要：The effects of elevated nitrogen deposition on soil microbial biomass carbon (C) and extractable dissolved organic carbon (DOC) in three types of forest of southern China were studied in November, 2004 and June, 2006. Plots were established in a pine forest (PF), a mixed pine and broad-leaved forest (MF) and monsoon evergreen broad-leaved forest (MEBF) in the Dinghushan Nature Reserve. Nitrogen treatments included a control (no N addition), low N (50 kg N/(hm2.a)), medium N (100 kg N/ (hm2. a)) and high N (150 kg N/(hm2. a)). Microbial biomass C and extractable DOC were determined using a chloro-form fumigation-extraction method. Results indicate that microbial biomass C and extractable DOC were higher in June, 2006 than in November, 2004 and higher in the MEBF than in the PF or the MF. The response of soil microbial biomass C and extractable DOC to nitrogen deposition varied depending on the forest type and the level of nitrogen treatment. In the PF or MF forests, no significantly different effects of nitrogen addition were found on soil microbial biomass C and extractable DOC. In the MEBF, however, the soil microbial biomass C generally decreased with increased nitrogen levels and high nitrogen addition significantly reduced soil microbial biomass C. The response of soil extractable DOC to added nitrogen in the MEBF shows the opposite trend to soil microbial biomass C. These results suggest that nitrogen deposition may increase the accumulation of soil organic carbon in the MEBF in the study region.
查看更多>>摘要：We tested the dynamics of nine enzymes during leaf litter decomposition in Xishuangbanna tropical rain-forest both in the field and laboratory to explore the response of enzyme dynamics to decomposition under different food-web structures. We used coarse and fine (1 mm and 100 μm mesh size, respectively) litterbags in the field to create different food-web structures during litter decomposition. Most soil macrofauna such as nematodes could access only the coarse mesh litterbags, leaving only microbiota, such as mites, in the fine mesh litterbags. In the laboratory, sterilization and inoculation were adopted to investigate different enzyme dynamics with nematodes or only microbiota participating in litter decomposition.Invertase and amylase increased more for shorter food webs at the early stages of decomposition, while activities of endocellulase, β-glucosidase, xylanase and polypheno-loxydase increased to their maxima at the later stages, but greater increase occurred with extended food webs.Invertase and amylase had negative relationships and endocellulase, β-glucosidase, xylanase and polyphenolox-ydase had positive relationships with litter decomposition (mass loss). The activities of enzymes responded to the process of litter decomposition. Invertase and amylase played key roles for microbiota utilizing the substrates at early stages of decomposition, while endocellulase, β-glucosidase, xylanase and polyphenoloxydase worked on the further decay of recalcitrant compounds at later stages.All enzymes related to carbon decay acted as effective indicators of litter decomposition. The decomposition of plant organic matter was essentially an enzymatic process.
查看更多>>摘要：Microenvironmental heterogeneity of soil phy-sical properties in 0-20 cm and 20-40 cm soil layers in a broad-leaved Pinus koraiensis forest gap in Xiao Xing'anl-ing Mountains were analyzed by geostatistical method.The results show that the amount of soil water, saturation water capacity, capillary water capacity and porosity in the top layer were greater than those in the lower layer, except for bulk density, where the opposite applied. Soil physical properties in the top soil layer had relatively higher ranges and coefficients of variation. The total and auto correlation spatial heterogeneity of soil physical properties in the top layer were larger than those in the lower layer. The soil water had a strong anisotropic structure in an easterly and northerly direction, but porosity shows isotropy in the same directions. With increasing spatial distance, the other three physical factors exhibited anisotropic structures. The mutual effect between semi-variograms of soil physical properties in the top layer within the spatial autocorrelation range was not significant. For spatial distribution of physical properties within different layers, the patches at the middle and lower ranks in the forest gap dominated.Patches at higher rank were only distributed in the 0-20 cm soil layer and were located north of the forest gap center.
查看更多>>摘要：We studied the nutrient cycle of a planted for-est ofPinus tabulaeformis in the Miyun Reservoir Water-shed, Beijing. Results show that the total biomass of P.tabulaeformis stands at age 29 in the experimental area is 92627 kg/hm2, and the total nutrient store is 695.17 kg/hm2 including nitrogen (N), phosphorus (P), kalium (K), calium (Ca) and magnesium (Mg). The sequence of their contents in different organs was given as follows: needle > branch >trunk > root. The annual amount of 85.37 kg/hm2 of five nutrient elements were assimilated by P. tabulaeformis,about 0.34% of the total store in soil, and 3.30% of available nutrient store in soil depth from 0 to 30 cm. The nutrient annual retention is 35.92 kg/hm2, annual returning 49.46kg/hm2, the rain input 26.04kg/hm2 to the five nutrient elements. The parameter absorption coefficient,utilization coefficient, cycle coefficient and turnover period were cited to describe the nutrient elements cycle characteristic of the planted forest ecosystem of P.tabulaeformis. The absorption coefficient is the ratio of plant nutrient element content to soil nutrient element content, and its sequence of five nutrient elements was given as follows: N > P > K > Ca > Mg. Utilization coef-ficient is the ratio of the nutrient element annual uptake amount to the nutrient element storage in standing crops,and its sequence of five nutrient elements was: Mg > K >P > N > Ca. The big utilization coefficient means more nutrients stored in the plant. The cycle coefficient is the ratio of the nutrient element annual return amount to the nutrient element annual uptake amount, its sequence:Ca > N > P > K > Mg. Turnover period is the ratio of the nutrient storage in the crops to the annual returning, its sequence: Mg > K > P > N > Ca.
查看更多>>摘要：The effect of vegetation on the water recycling of a land ecological system is considerably significant.Understanding the relationship between vegetation and runoff changes will benefit regional eco-environmental and water resources management. Based on paired catchments and time trend studies, a number of studies had been undertaken to establish the relationship between vegetation cover and water yield. We obtained some results from paired watersheds by focusing on changes at various time scales. At the mean annual scale the runoff changes resulting from vegetation alteration can be predicted using Zhang's curves. The absolute change of runoff due to vegetation alteration in a humid area is larger than that in the dry region, while the relative change is reverse. At the annual scale, it takes 15-20 years or longer in the arid region for catchments to reach a new equilibrium after afforestation,and under natural restoration, it takes about a hundred years.The vegetation changes have a proportionally larger impact on low flow at the seasonal scale. For catchments in arid regions,relative changes in low flow sections of the flow duration curve will be much more significant compared with that in the high flow section, leading to increased number of zero-flow days. However, in humid regions, changes in runoff tend to be much more uniform.
查看更多>>摘要：We excavated soil to study root distribution in Haloxylon ammodendron seedlings grown with different amounts of irrigation (35, 24.5 and 14 kg water for each plant each time) in the hinterland of the Taklimakan Desert.The results indicated that: 1) With decreasing irrigation amounts, the root biomass tended to be distributed in deeper soil layers. Underground biomass had a signifi-cantly negative logarithmic relationship with soil depth under different irrigation amounts. 2) Maximum horizontal spread of roots was twice that of vertical root spread, and horizontal distribution of root biomass was similar under all irrigation amounts. 3) Vertical distribution of fine roots was nearly consistent with vertical changes in soil moisture, and all had a unimodal curve; but peak values of fine root biomass in different soil layers varied with different irrigation amounts. The smaller the amount of irrigation, the deeper were the fine roots concentrated in soil layers. 4) Root length, root surface area and root volume all exhibited a unimodal curve under different irrigation amounts; the less the irrigation amount, the deeper the peak values appeared in soil layers. 5) Root- shoot ratio and ratio of vertical root depth to plant height both increased as irrigation amounts decreased.
查看更多>>摘要：Dynamic changes of soil erosion affected by conversion of farmland to forest or grassland in the Yanhe River Basin were analyzed based on the revised universal soil loss equation (RUSLE). The RUSLE variables were selected and calculated reasonably using the GIS techni-que. Results show that: 1) After the conversion of farmland to forest or grassland, soil erosion decreased greatly.Compared with soil erosion in period of 1986 to 1997, the soil erosion amount had been reduced on the average by 30.6% by 2000; 2) Of the different land uses, slope farmland, especially the steep slope land had the greatest impact on soil erosion. The conversion of forest or grassland was the main driving force for the reduction of soil erosion; 3) In the short term, soil erosion was mainly controlled by C-factor, implying that the adjustment of land use structure might be an effective approach to reduce soil erosion.
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