不同CO_2浓度下大豆叶片的水分利用效率比较

为探究水分利用效率(WUE)对生态系统水循环和碳循环相互作用的影响,本研究利用光合作用对光响应的机理模型构建内禀水分利用效率模型和瞬时水分利用效率模型,并利用2个模型拟合大豆叶片的内禀水分利用效率(WUEi)和瞬时水分利用效率(WUEinst)。结果表明,瞬时水分利用效率随着CO2浓度的增加而增大;内禀水分利用效率则不存在明显的变化规律。CO2浓度为600μmol·mol-1时的最大瞬时水分利用效率和最大内禀水分利用效率分别是300μmol·mol-1CO2下的2. 82倍和1. 94倍。将内禀水分利用效率和瞬时水分利用效率换算成相同的单位(如μmol CO2·mol-1H2O或μmol CO2·mmol-1H2O),后者是前者的39倍,甚至更多。综上所述,利用瞬时水分利用效率能更真实地反映出大豆叶片的水分利用效率。本研究为定量研究植物叶片水分利用效率的变化规律提供了数学工具。

A study on the simulation of carbon and water fluxes of Dangxiong alpine meadow and its response to climate change

The alpine meadow ecosystem accounts for 27%of the total area of the Tibetan Plateau and is also one of the most important vegetation types.The Dangxiong alpine meadow ecosystem,located in the south-central part of the Tibetan Plateau,is a typical example.To understand the carbon and water fluxes,water use efficiency(WUE),and their responses to future climate change for the alpine meadow ecosystem in the Dangxiong area,two parameter estimation methods,the Model-independent Parameter Estimation(PEST)and the Dynamic Dimensions Search(DDS),were used to optimize the Biome-BGC model.Then,the gross primary productivity(GPP)and evapotranspiration(ET)were simulated.The results show that the DDS parameter calibration method has a better performance.The annual GPP and ET show an increasing trend,while the WUE shows a decreasing trend.Meanwhile,ET and GPP reach their peaks in July and August,respectively,and WUE shows a“dual-peak”pattern,reaching peaks in May and November.Furthermore,according to the simulation results for the next nearly 100 years,the ensemble average GPP and ET exhibit a significant increasing trend,and the growth rate under the SSP5–8.5 scenario is greater than that under the SSP2–4.5 scenario.WUE shows an increasing trend under the SSP2–4.5 scenario and a significant increasing trend under the SSP5–8.5 scenario.This study has important scientific significance for carbon and water cycle prediction and vegetation ecological protection on the Tibetan Plateau.

Impacts of climate change on agricultural water resources and adaptation on the North China Plain

Climate change is having a considerable impact on the availability of water resources for agricultural production on the North China Plain （NCP）, where the shortage of water is currently disturbing the stability and sustainability of agricultural production with respect to the drying tendency since the 1950s. However, although potential evapotranspiration （ET） has shown a decreasing trend under climate change, actual ET has slightly increased with an acceleration in hydrological cycling. Global climate model （GCM） ensemble projections predict that by the 2050s, the increased crop water demand and intensified ET resulting from global warming will reduce water resources surplus （Precipitation-ET） about 4%-24% and increase significantly the irrigation water demand in crop growth periods. This study assesses possible mitigation and adaptation measures for enabling agricultural sustainability. It is revealed that reducing the sowing area of winter wheat （3.0%-15.9%） in water-limited basins, together with improvement in crop water-use efficiency would effectively mitigate water shortages and intensify the resilience of agricultural systems to climate change.

Effects of Elevated CO_2 and Drought on Plant Physiology, Soil Carbon and Soil Enzyme Activities

Global climate models have indicated high probability of drought occurrences in the coming future decades due to the impacts of climate change caused by a mass release of CO2. Thus, climate change regarding elevated ambient CO2 and drought may consequently affect the growth of crops. In this study, plant physiology, soil carbon, and soil enzyme activities were measured to investigate the impacts of elevated C02 and drought stress on a Stagn[c Anthrosol planted with soybean （Glycine ma,z）. Treatments of two CO2 levels, three soil moisture levels, and two soil cover types were established. The results indicated that elevated CO2 and drought stress significantly affected plant physiology. The inhibition of plant physiology by drought stress was mediated via prompted photosynthesis and water use efficiency under elevated CO2 conditions. Elevated CO2 resulted in a longer retention time of dissolved organic carbon （DOC） in soil, probably by improving the soil water effectiveness for organic decomposition and mineralization. Drought stress significantly decreased C：N ratio and microbial biomass carbon （MBC）, but the interactive effects of drought stress and CO2 on them were not significant. Elevated CO2 induced an increase in invertase and catalase activities through stimulated plant root exudation. These results suggested that drought stress had significant negative impacts on plant physiology, soil carbon, and soil enzyme activities, whereas elevated CO2 and plant physiological feedbacks indirectly ameliorated these impacts.

A Factor Decomposing Model of Water Use Efficiency at Sector Level and Its Application in Beijing

The paper explores the contribution of different factors affecting water use efficiency(WUE) of each sector and explores ways to improve WUE.A new Multi-Sector and Multi-Factors Logarithmic Mean Divisia Index(MLMDI) decomposition method was developed that enabled the identification of WUE by sector into 11 factors in terms of their order of importance.An application to Beijing at the 19 sector level was made for the period between 2002–2007.The water conservation effects of six measures proposed during the 12th-Five-Year-Plan of Beijing were assessed.It was found that,to decrease the transferred out and export of agriculture products and increasing water prices would be the top two most effective measures to promote water conservation.While the adjustment of direct water use structure would contribute in less significant way,the adjustment of industrial structure would have a negative effect.