中国东部南北样带森林生态系统蒸腾与蒸散比值估算（英文）

The ratio of transpiration to evapotranspiration(T/ET) is a key parameter for quantifying water use efficiency of ecosystems and understanding the interaction between ecosystem carbon uptake and water cycling in the context of global change. The estimation of T/ET has been paid increasing attention from the scientific community in recent years globally. In this paper, we used the Priestly-Taylor Jet Propulsion Laboratory Model(PT-JPL) driven by regional remote sensing data and gridded meteorological data, to simulate the T/ET in forest ecosystems along the North-South Transect of East China(NSTEC) during 2001–2010, and to analyze the spatial distribution and temporal variation of T/ET, as well as the factors influencing the variation in T/ET. The results showed that:(1) The PT-JPL model is suitable for the simulation of evapotranspiration and its components of forest ecosystems in Eastern China, and has relatively good stability and reliability.(2) Spatial distribution of T/ET in forest ecosystems along NSTEC was heterogeneous, i.e., T/ET was higher in the north and lower in the south, with an averaged value of 0.69; and the inter-annual variation of T/ET showed a significantly increasing trend, with an increment of 0.007/yr(p0.01).(3) Seasonal and inter-annual variations of T/ET had different dominant factors. Temperature and EVI can explain around 90%(p0.01) of the seasonal variation in T/ET, while the inter-annual variation in T/ET was mainly controlled by EVI(53%, p0.05).     

Spatial variation of altitudinal belts as dividing index between warm temperate and subtropical zones in the Qinling-Daba Mountains

To determine the dividing index between warm temperate and subtropical zones based on the spectra of altitudinal belts,this paper collected 33 spectra of altitudinal belts in the Qinling-Daba Mountains from published literatures and then analyzed the structures and the spatial patterns from south to north,from west to east and based on exposure directions.The results show that:1)From south to north,the basal belt gradually changes from subtropical evergreen broadleaf forest to warm temperate deciduous broadleaf forest;the spectra of altitudinal belts change from complex to simple;the dominant belt changes from montane broadleaf-conifer mixed forest and evergreen-deciduous broadleaf mixed forest to deciduous broadleaf forest.2)From west to east,the structures of the altitudinal belt spectra show complexity in the east and west but simplicity in the middle section;the upper limits of both the evergreen-deciduous broadleaf mixed forest belt and montane deciduous broadleaf forest belt present a quadratic curve distribution pattern in the longitudinal direction.However,the upper limit of the montane broadleaf-conifer mixed forest belt exhibits a nearly linear decrease in the west-east direction.3)Both the north and south slopes in the Qinling Mountains have the similar basal belt,whereas it varies greatly between the north and south slopes in the Daba Mountains.Comparably,dominant belts are very similar in the Qinling Mountains and the north slope of the Daba Mountains,but the south slope of the Daba Mountains has its own unique dominant belt:evergreen-deciduous broadleaf mixed forest.This implies that the Daba Mountains are more appropriate than the Qinling Mountains to act as the boundary between subtropical and warm-temperate zones in central China.     

Water sources of plants and groundwater in typical ecosystems in the lower reaches of the Heihe River Basin

Stable oxygen and hydrogen isotopic compositions （δ18O and δD） of soil water and shallow groundwater of a riparian forest, an artificial shrub forest, and Gobi of the lower reaches of the Heihe River Basin are used to study the recharge water sources of those ecosystems. IsoSource software is used to determine the δ180 values for root water of Populous euphratica and Tamarix ramosissima in the riparian forest ecosystem, Haloxylon ammodendron in the artificial shrub forest, and Reaumuria soongorica in the Gobi, as well as for local soil water and groundwater, and precipitation in the upper reaches of the Heihe River Basin. Our results showed that soil water and shallow groundwater of the riparian forest and the artificial shrub forest were recharged by river water which originated from precipitation in the upper reaches, and strong evaporation occurred in the artificial shrub forest. Soil water of the Gobi was not affected by Heihe River water due to this area being far away from the river channel. The main water sources of Populous euphratica were from 40-60-cm soil water and groundwater, and of Tamarix ramosissima were from 40-80-cm soil water in the riparian forest ecosystem. In the artificial forest, Haloxylon ammodendron used 200-cm saturated-layer soil water and shallow groundwater. The Reaumuria soongorica mainly used soil water from the 175-200-cm depth in the Gobi. Therefore, soil water and groundwater are the main water sources which maintain survival and growth of the plants in the extremely arid regions of the lower reaches of the Heihe River Basin.     

中国科技资源配置效率测度及其时空格局演变特征(英文)

According to the connotation and structure of science and technology resources and some relevant data of more than 286 cities at prefecture level and above during 2001–2010, using modified method—Data Envelopment Analysis(DEA), science and technology(ST) resource allocation efficiency of different cities in different periods has been figured out, which, uncovers the distributional difference and change law of ST resource allocation efficiency from the time-space dimension. Based on that, this paper has analyzed and discussed the spatial distribution pattern and evolution trend of ST resource allocation efficiency in different cities by virtue of the Exploratory Spatial Data Analysis(ESDA). It turned out that:(1) the average of ST resource allocation efficiency in cities at prefecture level and above has always stayed at low levels, moreover, with repeated fluctuations between high and low, which shows a decreasing trend year by year. Besides, the gap between the East and the West is widening.(2) The asymmetrical distribution of ST resource allocation efficiency presents a spatial pattern of successively decreasing from Eastern China, Central China to Western China. The cities whose ST resource allocation efficiency are at higher level and high level take on a cluster distribution, which fits well with the 23 forming urban agglomerations in China.(3) The coupling degree between ST resource allocation efficiency and economic environment assumes a certain positive correlation, but not completely the same. The differentiation of ST resource allocation efficiency is common in regional development, whose existence and evolution are directly or indirectly influenced by and regarded as the reflection of many elements, such as geographical location, the natural endowment and environment of ST resources and so on.(4) In the perspective of the evolution of spatial structure, ST resource allocation efficiency of the cities at prefecture level and above shows a notable spatial autocorrelation, which in every period presents a positive correlation. The spatial distribution of ST resource allocation efficiency in neighboring cities seems to be similar in group, which tends to escalate stepwise. Meanwhile, the whole differentiation of geographical space has a diminishing tendency.(5) Viewed from LISA agglomeration map ofST resource allocation efficiency in different periods, four agglomeration types have changed differently in spatial location and the range of spatial agglomeration. And the continuity of ST resource allocation efficiency in geographical space is gradually increasing.     

历史及未来气候变化下中国潜在植被NPP的脆弱性研究（英文）

Using the Integrated Biosphere Simulator, a dynamic vegetation model, this study initially simulated the net primary productivity(NPP) dynamics of China's potential vegetation in the past 55 years(1961–2015) and in the future 35 years(2016–2050). Then, taking the NPP of the potential vegetation in average climate conditions during 1986–2005 as the basis for evaluation, this study examined whether the potential vegetation adapts to climate change or not. Meanwhile, the degree of inadaptability was evaluated. Finally, the NPP vulnerability of the potential vegetation was evaluated by synthesizing the frequency and degrees of inadaptability to climate change. In the past 55 years, the NPP of desert ecosystems in the south of the Tianshan Mountains and grassland ecosystems in the north of China and in western Tibetan Plateau was prone to the effect of climate change. The NPP of most forest ecosystems was not prone to the influence of climate change. The low NPP vulnerability to climate change of the evergreen broad-leaved and coniferous forests was observed. Furthermore, the NPP of the desert ecosystems in the north of the Tianshan Mountains and grassland ecosystems in the central and eastern Tibetan Plateau also had low vulnerability to climate change. In the next 35 years, the NPP vulnerability to climate change would reduce the forest–steppe in the Songliao Plain, the deciduous broad-leaved forests in the warm temperate zone, and the alpine steppe in the central and western Tibetan Plateau. The NPP vulnerability would significantly increase of the temperate desert in the Junggar Basin and the alpine desert in the Kunlun Mountains. The NPP vulnerability of the subtropical evergreen broad-leaved forests would also increase. The area of the regions with increased vulnerability would account for 27.5% of China.     

珠江流域东江至虎门出口的河流有机碳来源与输运特征（英文）

Transport of organic carbon via rivers to estuary is a significant geochemical process in the global carbon cycle.This paper presents bulk total organic carbon(TOC) from the Dongjiang catchment to the adjacent Humen outlet,and discusses the applicability of δ13C and ratio of carbon to nitrogen(C/N) as indicators for sources of organic matter in the surface sediments.Survey results showed that organic carbon concentration in summer were higher than in the winter.An elevated trend of TOC occurred along the river to the Humen outlet in both surveys,and the highest mean values of dissolved and particular organic carbon(DOC~279 μmol L–1 and POC~163 μmol L–1) were observed in the urban deltaic region in summer flood flow.Winter samples had a wide range of δ13C and C/N(δ13C –24.6‰ to –30.0‰,C/N 4–13),and summer ones varied slightly(δ13C –24.2‰ to –27.6‰,C/N 6–18).As results suggest that POC in the three zones of upstream-delta-outlet dominantly came from riverbank soil,phytoplankton and agricultural C3 plants in winter,whereas main sources were from the riverbank and mangrove soil in summer.Moreover,anthropogenic sewage inputs had 11% and 7% contribution to POC in the deltaic and outlet.Transport accompanied with seasonal freshwater variation,phytoplankton production and degradation,and removal behavior caused variation of organic carbon concentration.The results also discovered that TOC export bulk in Dongjiang was approximately one quarter of Humen flux in the dry flow,and anthropogenic activity significantly impacted the river export contribution.     

上海市崇明岛农田土壤重金属的环境质量评价(英文)

The environmental quality of heavy metals (Pb,Cd,Cr,As,Hg) in agricultural surface soil of Chongming Island was assessed by national,local and professional standards based on a large scale investigation,in which 28 samples from vegetable plots,65 samples from paddy fields and 9 samples from watermelon fields were collected from whole island area. Results showed that the average concentration of Pb,Cd,Cr,As and Hg was 21.6 mg·kg-1,0.176 mg·kg-1,69.4 mg·kg-1,9.209 mg·kg-1 and 0.128 mg·kg-1,respectively. Compared with the background value of Shanghai City soil,except for Pb and Cr,all the other heavy metals average concentrations in Chongming Island agricultural surface soil exceeded their corresponding natural-background values. The concentrations of Cd,As and Hg were 33.0%,1.2% and 26.3% higher than the background value of Shanghai City,respectively. In addition,inverse distance interpolation (IDW) tool of GIS was also applied to study the spatial variation of heavy metals. The results indicated that most of agricultural soil quality was good,and the ratio of ecological,good soil,certified soil and disqualified soil were 1.26%,97.1%,1.47% and 0.12%,respectively. About 10.1%,85.7%,27.0%,55.4% and 55.2% soil samples exceeded the Pb,Cd,Cr,As and Hg background value of Shanghai City,respectively. Among these three land use type soils,vegetable soil was most seriously polluted by heavy metals,which is probably related to the over-application of pesticides. The annual deposition fluxes of Pb,Cd,As and Hg were 7736 μg.m-2.a-1,208 μg.m-2.a-1,2238 μg.m-2.a-1 and 52.8 μg.m-2.a-1,respectively. Crop straw burning was the important source of heavy metals of atmospheric deposition,and atmospheric deposition contributed a lot to heavy metals in agricultural soil in Chongming Island.     

内蒙古农牧交错带土地利用变化对土壤碳储量的影响研究（英文）

Soil organic carbon(SOC) stocks in terrestrial ecosystems vary considerably with land use types. Grassland, forest, and cropland coexist in the agro-pastoral ecotone of Inner Mongolia, China. Using SOC data compiled from literature and field investigations, this study compared SOC stocks and their vertical distributions among three types of ecosystems. The results indicate that grassland had the largest SOC stock, which was 1.5-and 1.8-folds more than stocks in forest and cropland, respectively. Relative to the stock in 0–100 cm depth, grassland held more than 40% of its SOC stock in the upper 20 cm soil layer; forest and cropland both held over 30% of their respective SOC stocks in the upper 20 cm soil layer. SOC stocks in grazed grasslands were remarkably promoted after ≥20 years of grazing exclusion. Conservational cultivation substantially increased the SOC stocks in cropland, especially in the 0–40 cm depth. Stand ages, tree species, and forest types did not have obvious impacts on forest SOC stocks in the study area likely due to the younger stand ages. Our study implies that soil carbon loss should be taken into account during the implementation of ecological projects, such as reclamation and afforestation, in the arid and semi-arid regions of China.     

Microbial production of CO2 in red soil in Stone Forest National Park

Lunan stone forest is a kind of typical karst in China,Which is mainly developed under red soil.In the winter of 1999,three study sites were chosen in stone forest national park according to vegetation cover,geomporphologic location and soil types,CO2 concentration was measured with Gastec punp at different dephts of soil (20,40,60cm) and at the same time soil samples were gatered and soil properties such as soil moisure,pH,soil organic content were analyzed and the total nmuber of viable microbes were counted in laboratory,In the study,dependent variable was chosen as the mean soil log(PCO2),and soil properties were chosen as the independent variables.Multiple stepwise regression analysis showed that the totla amount of microbes and soil moisture are the best indicators of the CO2 production,With the equation LOG(PCO2)=-0.039(TNM)-0.056 (Mo) 1.215 accounting for 86% of the variation of the soil CO2 concentration,where TNM is the total number of microbes in teh soil and Mo is the moisture of soil sample.     

中国东部南北样带森林生态系统蒸腾与蒸散比值（T/ET）时空变化

植被蒸腾与蒸散的比值（transpiration/evapotranspiration, T/ET）表征了植被蒸腾对生态系统蒸散的贡献率,是准确量化生态系统水分利用效率的关键参数,对研究植被水分运移的生理生态机理以及碳水循环关系具有重要意义。基于站点数据验证PT-JPL模型（Priestly-Taylor Jet Propulsion Laboratory Model）模拟精度,集成遥感数据和气象栅格数据模拟中国东部南北样带森林生态系统2001-2010年T/ET,并分析其时空变化及影响因子。结果表明：① PT-JPL模型适用于中国东部森林生态系统蒸散及其组分模拟,具有较高的稳定性和可靠性;② 中国东部南北样带森林生态系统T/ET空间差异显著,整体呈南部低、北部高,主要由夏季T/ET空间格局主导;样带整体T/ET均值为0.69,2001-2010年呈显著缓慢上升趋势,增幅为0.007/yr（p < 0.01）;③ T/ET季节和年际变异的主控因子不同：温度和EVI是影响T/ET季节变异的关键因子,两者均可解释T/ET季节变异的90%左右（p < 0.01）;而T/ET的年际变异则主要受EVI影响,解释率为53%（p < 0.05）。     

Changes in soil organic carbon and other physical soil properties along adjacent Mediterranean forest, grassland, and cropland ecosystems in Turkey

Cultivation, overgrazing, and overharvesting are seriously degrading forest and grassland ecosystems in the Taurus Mountains of the southern Mediterranean region of Turkey. This study investigated the effects of changes on soil organic carbon (SOC) content and other physical soil properties over a 12-year period in three adjacent ecosystems in a Mediterranean plateau. The ecosystems were cropland (converted from grasslands in 1990), open forest, and grassland. Soil samples from two depths, 0–10 and 10–20 cm, were collected for chemical and physical analyses at each of cropland, open forest, and grassland ecosystems. SOC pools at the 0–20 cm depth of cropland, forest, and grassland ecosystems were estimated at 32,636, 56,480, and 57,317 kg ha⁻¹, respectively. Conversion of grassland into cropland during the 12-year period increased the bulk density by 10.5% and soil erodibility by 46.2%; it decreased SOM by 48.8%, SOC content by 43%, available water capacity (AWC) by 30.5%, and total porosity by 9.1% for the 0–20 cm soil depth (p<0.001). The correlation matrix revealed that SOC content was positively correlated with AWC, total porosity, mean weight diameter (MWD), forest, and grassland, and negatively with bulk density, pH, soil erodibility factor, and cropland. The multiple regression (MLR) models indicated that any two of the three ecosystems and one of the two soil depths accounted for 86.5% of variation in mean SOC values ((p<0.001).     

黑河流域植被水分利用效率时空变化特征及其与气候因子的关系

利用中分辨率成像光谱仪（MODIS）产品总初级生产力（GPP）、蒸散发（ET）及气象数据估算了黑河流域植被水分利用效率（WUE）,分析了WUE的时空变化及与气候因子的相关性。结果表明：2005-2014年黑河流域单位面积上多年平均GPP为314.44 gC·m^-2,ET为363.35 mm,多年平均植被WUE为1.15 gC·mm^-1H₂O·m^-2;黑河流域WUE总体呈由南向北递增的空间分布格局,年内呈现单峰型结构,WUE高值区分布在酒泉-临泽东西线上及额济纳斯荒漠河岸林地带,托勒的东南部地区为WUE低值区;黑河流域生态系统WUE具有明显的季节变化规律,表现为夏季 > 春季 > 秋季 > 冬季的特征,夏季为1.32 gC·mm^-1H₂O·m^-2,冬季为0.75 gC·mm^-1H₂O·m^-2;水分利用效率年均分布与倾向率的增加具有一定的对应关系,莺落峡、民乐一带是WUE的高值区也是整个流域倾向率快速增长区,在WUE稳定性方面,中下游绿洲区变化最为显著,上游高海拔区、中下游戈壁区变化不显著;WUE与年降水量、年平均气温以负相关为主,其中降水是影响植被WUE的主要因素,正相关的区域分布在山丹县、民乐县东部、肃南裕固族自治县南部湖泊区域,而气温只在下游绿洲区呈正相关。     

Response of the water use efficiency of natural vegetation to drought in Northeast China

Drought has become a problem that is universally faced by global terrestrial ecosystems. Northeast China is located in a region sensitive to global climate changes, and one of the main impacts of climate changes in Northeast China is manifested as drought in growing seasons. This study analyzes the spatio-temporal evolution law of the water use efficiency (WUE) of the main natural vegetation (i.e., cold-temperate coniferous forests, temperate pine-broad-leaved mixed forests, warm-temperate deciduous broad-leaved forests, and grasslands) in Northeast China based on public MODIS data products, including MCD12Q1, MOD15A2H, MOD16A2, and MOD17A3H, and meteorological data from 2002 to 2013. The influence of drought events on the WUE of different vegetation types and their response to drought events are also investigated. The study findings are as follows: (1) drought in Northeast China frequently occurs in the regions stretching from 114.55°E to 120.90°E, and the percentage of drought area among the forests is lower than that among the grasslands during these years; (2) the annual average WUE of the natural vegetation ranges from 0.82 to 1.08 C/kg^-1H₂O, and the WUE of forests (0.82 to 1.08 C/kg^-1H₂O) is universally higher than that of grasslands (0.84 to 0.99 C/kg^-1H₂O); (3) in 2008, the regions where the WUE in drought conditions is higher than that in normal water conditions account for 86.11% of the study area, and a significant linear positive correlation is found between the WUE in drought conditions and the WUE in normal water conditions, whereas the degree of drought does not influence the WUE of the natural vegetation in an obviously linear manner; and (4) the WUE for the cold-temperate coniferous forests and temperate pine-broad-leaved mixed forests with a high ET or low NPP is more likely to rise in drought conditions; the WUE for the grasslands with a low Evapotranspiration (ET), Net Primary Production (NPP), and Leaf Area Index (LAI) is more likely to rise in drought conditions; and the ET, NPP, and LAI have no significant influence on the WUE for the warm-temperate deciduous broad-leaved forests in drought conditions. This study contributes to improving the evaluation of the influence of drought on natural ecosystems.     

Spatiotemporal variations of water use efficiency and its driving factors in Inner Mongolia from 2001 to 2020

Water use efficiency (WUE) is an important variable to explore coupled relationships in carbon and water cycles. In this study, we first compared the spatial variations of annual gross primary productivity (GPP) and evapotranspiration (ET) using four GPP and ET products. Second, we selected the products closest to the flux towers data to estimate WUE. Finally, we quantitatively analyzed the impact of climate change and soil water content on WUE. The results showed that: (1) Four GPP and ET products provided good performance, with GOSIF-GPP and FLDAS-ET exhibiting a higher correlation and the smallest errors with the flux tower data. (2) The spatial pattern of WUE is consistent with that of GPP and ET, gradually decreasing from the northeast to the southwest. Higher WUE values appeared in the northeast forest ecosystem, and lower WUE values occurred in the western Gobi Desert, with a value of 0.28 gC m^?2 mm^?1. The GPP and ET products showed an increasing trend, while WUE showed a decreasing trend (55.15%) from 2001 to 2020. (3) The spatial relationship between WUE and driving factors reveal the variations in WUE of Inner Mongolia are mainly affected by soil moisture between 0 and 10 cm (SM0-10cm), vapor pressure deficit (VPD), and precipitation, respectively. (4) In arid regions, VPD and precipitation exhibit a major influence on WUE. An increase in VPD and precipitation has a negative and positive effect on WUE, with threshold values of approximately 0.36 kPa and 426 mm, respectively. (5) In humid regions, SM0-10cm, VPD, SM10-40cm, and SM40-100cm exert a significant impact on WUE, especially SM0-10cm, and weakens with increasing soil depths, these differences may be related to physiological structure and living characteristics of vegetation types in different climate regimes. Our results emphasize the importance of VPD and soil moisture in regional variability in WUE.     

Physiological and growth responses of Populus davidiana ecotypes to different soil water contents

Changes in dry matter accumulation and allocation, gas exchange, abscisic acid content (ABA) and water use efficiency (WUE) of three contrasting Populus davidiana ecotypes were recorded after exposure to five different soil water contents. The ecotypes used were from dry, middle and wet climate regions, respectively. In the controlled environment study, five different soil water contents which were watered to 100%, 80%, 60%, 40% and 20% field capacity were used, respectively. Significant differences in height growth (HT), total biomass (TB), total leaf area (LA), total leaf number (TLN), specific leaf area (SLA), root/shoot ratio (RS), net photosynthesis (A), transpiration (E), stomatal conductance (C), transpiration efficiency (WUE_T) and instantaneous water use efficiency (WUE_i) between the ecotypes were detected under all soil water contents. Ecotypic differences in ABA and carbon isotope composition (δ¹³C) were also detected under low soil water contents, but these differences were not significant under high soil water content. Compared with the wet climate ecotype, the dry climate ecotype had lower HT, TB, LA, TLN, SLA, A, E and C, and higher RS, WUE_T and WUE_i under all soil water contents. On the other hand, the dry climate ecotype also exhibited higher ABA and δ¹³C as affected by low soil water contents than the wet climate ecotype. These morphological and physiological responses to water availability showed that the different ecotypes may employ different survival strategies under drought at the initial phase of seedling growth and establishment. The wet climate ecotype possesses a prodigal water use strategy and quick growth, while the dry climate ecotype exhibits a conservative water use strategies and slow growth.     

伏牛山地区森林生态系统服务权衡/协同效应多尺度分析

森林生态系统服务权衡与协同研究已成为当前相关学科的研究热点和前沿,对服务权衡与协同关系的多尺度分析有助于更加有效地实施森林资源管理。综合森林类型图、NDVI、气象和土壤等多源数据,借助CASA模型、InVEST 3.2模型和ArcGIS 10.2软件,开展伏牛山地区森林生态系统服务评估,运用空间叠置方法从多个空间尺度（区域、南北坡、垂直带）探讨服务权衡与协同效应。结果表明：① 研究区森林生态系统平均蓄积量为49.26 m ³/hm ²,碳密度为156.94 t/hm ²,供水深度为494.46 mm,土壤保持量为955.4 t/hm ²,生境质量指数为0.79。② 区域尺度上,28.79%的森林服务之间存在高协同效应,10.15%的森林存在低协同效应,61.06%的森林存在强权衡和弱权衡效应。③ 南北坡尺度上,南坡服务之间的协同关系优于北坡。垂直带尺度上,南坡中山落叶阔叶林带（SIII）服务之间协同关系最好,北坡低山落叶阔叶林带（NI）协同关系最差。     

Spatial variability of selected soil properties in relation to land use and slope position in Gelana sub-watershed,Northern highlands of Ethiopia

Land degradation resulting from land-use changes and soil erosion has been a serious environmental problem in Ethiopia. This study addressed the effects of land use and slope position on soil physical and chemical properties in the Gelana sub-watershed, Northern highlands of Ethiopia. A total of 63 soil samples were collected and analyzed using a two-way ANOVA. Results showed that clay, soil pH, soil organic matter, total nitrogen, cation exchange capacity, and exchangeable base contents of the cultivated land were significantly (p < 0.001) lower than those of the forest land, while soil bulk density, available phosphorous, and percentage base saturation were higher for cultivated land than forest land. In general, soil fertility declines as land use changes from forest to grazing and cultivated lands. Sand, clay, bulk density, soil pH, organic matter, total nitrogen, carbon:nitrogen ratio, available phosphorous, cation exchange capacity, exchangeable cations, and percentage base saturation showed significant variation due to slope position differences. Therefore, the study reinforces the need for integrated watershed management for sustainable agricultural production in the study area.     

Carbon accumulation, nitrogen and phosphorus use efficiency of Sophora davidii seedlings in response to nitrogen supply and water stress

A greenhouse experiment was conducted to explore whether additional nitrogen (N) supply could enhance carbon (C) accumulation, and phosphorus (P) use efficiency (NUE_P) of Sophora davidii seedlings under dry conditions. Two-month-old seedlings were subjected to a completely randomized design with three water (80, 40 and 20% water field capacity (FC)) and three N supply (N0: 0, Nl: 92 and Nh: 184 mg N kg⁻¹ soil) regimes. Water stress decreased C, N and P accumulation, NUE_P, N and P uptake efficiency (NUtE_N and NUtE_P) regardless of N supply. The S. davidii seedlings exhibited strong responses to N supply, but the responses were not consistent with the various N supply levels. Nl increased C, N and P accumulation, and improved NUE_P, NUtE_N and NUtE_P in the same water treatment. In contrast, Nh did few or even depress effects on C, N and P accumulation, and NUE_P, although NUtE_N and NUtE_P increased with Nh in the same water treatment. Even so, NUE_N decreased with increase of N supply in the same water treatment. The results suggested that appropriate or low N supply should be recommended for S. davidii seedling establishment in dry environment by improving C accumulation and NUE_P.     

根系分隔对小麦玉米套作田土壤水分状况的影响

2009年3-10月通过田间试验研究了小麦玉米套作田塑料薄膜隔根（PW/C）、尼龙网隔根（NW/C）、不隔根（W/C）及单作玉米（C）和单作小麦（W）的土壤水分状况。结果表明：以单作小麦、单作玉米加权平均为对照,W/C、NW/C和PW/C处理分别显著提高经济产量33.60 %、26.93%和24.69%,增大耗水量-0.2%、1.02%和6.69%,显著提高水分利用效率34.93%、26.67%和17.80%。W/C处理较NW/C和PW/C处理分别提高经济产量5.25%和7.14%,降低耗水量1.21%和6.64%,提高水分利用效率6.52%和14.54%。小麦玉米共生期,土壤水分在套作群体组分间能够优化分配,根系分隔显著降低了作物群体产量及对土壤水分的利用效率。