粮食作物产量对气候变暖的响应

Response of grain crop yields to climate warming

玉米、小麦和水稻是主要粮食作物,总收获面积和总产量分别占全球禾谷类作物的79%和90%.气候变暖导致主要粮食作物减产.玉米对气候变暖的敏感性高于小麦,温度升高1℃导致全球玉米减产3%~12%,小麦减产3%~9%;温度升高有利于中、高纬度地区水稻生产,但导致低纬度地区水稻减产.作物产量对气候变暖的响应呈非线性,当温度高于作物生长的适宜温度时,产量对气候变暖的敏感性随温度升高的幅度进一步增强.热带地区作物产量对气候变暖的敏感性高于温带地区;雨养农业区作物产量对气候变暖的敏感性高于灌溉农业区,灌溉可有效降低高温对作物产量的负面影响.大气CO_2浓度升高促进作物生长,CO_2施肥效应能在一定程度上补偿由于气候变暖导致的粮食作物减产.气候变暖导致粮食作物减产以及CO_2浓度升高促进作物生长已有共识,但对气候变暖下CO_2施肥效应的认知存在极大的不足,其主要原因是自然状态下CO_2浓度升高和增温对作物生长的交互作用的实验研究太少.未来研究重点应拓展FACE(free-air CO_2 enrichment)条件下的增温实验,通过不同CO_2浓度梯度下的增温实验,结合其他因子(水分、氮素等)的调控,精细量化不同条件下的CO_2施肥效应,并据此发展和完善作物模型,进而客观评估未来气候变暖情景下CO_2的施肥效应及其对作物减产的补偿作用.

World population,now 7.55 billion people,will increase to 9.4–10.2 billion in 2050 and 9.6–13.2 billion in 2100.Global food demand in 2050 is projected to increase by at least 60% above 2006 levels to meet the world’s food needs for growing populations.Maize,wheat and rice are the main grain crops in the world,accounting together for approximately 90% of global cereal crop yields.Over the last six decades,global mean surface temperature increased at a rate of 0.12°C per decade.Relative to the period of 1986–2005,global surface temperature is projected to increase 1–3.7°C in the late 21st century.Climate warming has led to a reduction of grain crop yields.The sensitivity of maize to climate warming is more pronounced than that of wheat.Global yields of maize and wheat decreased by 3%–12%and 3%–9% for 1°C warming,respectively.Warming is likely beneficial to rice production in mid-and high-latitudes,but leads to loss of rice yield in low-latitude.Yield losses induced by climate warming are greater in tropical regions than in temperate regions,with the loss of 5%–12% per degree warming for tropical maize and wheat and less than 5% for temperate maize and wheat.Crop yields are more sensitive to climate warming in rain-fed agriculture than in irrigated agriculture.Irrigation can effectively reduce the negative impact of warming on crop yield.Response of crop yields to climate warming is nonlinear.The sensitivity of crop yield to climate warming is further enhanced with increasing temperature,when the temperature is above the optimum thresholds of crop growth.Elevated atmospheric CO_2 concentration could benefit crop yields by increasing photosynthesis,and thus offset the yield losses due to climate warming to some extent.The fertilization effect of rising CO_2 concentration on crop yield in the future seems optimistic from model simulations.However,there is big uncertainty in the magnitude of the CO_2 effect and the significance of interactions with other factors.A primary reason for this uncertainty is the limited availability of experimental data on CO_2 responses for crops grown under various field conditions.Moreover,no models currently account for the interactions of CO_2 with temperature,varieties,water status,and nitrogen availability.The free-air CO_2 enrichment（FACE）technique remains the best platform to test plants under the open-field conditions.The future FACE experiments should focus on the responses of crop production to various levels of elevated CO_2 and interactions with warmer temperature,water status and nitrogen input.The uncertainties in CO_2 fertilization effect could be reduced when the field experiments are largely expanded.Furthermore,improving temperature and CO_2 relationships in models is essential to precisely assess the CO_2 fertilization effect at regional and/or global scales.