Simulation Of Maize Growth And Yield Under Climate Change In China

Climate change and its countermeasures are major global persistent issues faced today and future.There is a significant difference in climate between the north and the south in China.The overall trend of climate change is similar in each region,while there are also obvious differences in rainfall,radiation and countermeasures adopted.In this paper,maize,the largest grain yield in China,is taken as the object.Based on the data of Yangling field test site in the semi-arid and semi-humid area of the northwest semi-arid region,this study analyzed the effects of water stress on summer maize in different growth periods,and evaluated and improved the growth and yield simulated ability of CERES-Maize model under water stress condition;used the model to analyze the effects of the decrease of sunshine hours and daily maximum temperature and the change of cultivar on maize yield in Shaanxi Province;used the statistical model to analyze the effects of temperature increase and the north shift of maize planting area on the historical and future national maize yield.The study concludes as follows:?1?Effects of severe drought on the growth and development of maize.Field experiments conducted over four consecutive crop-growing seasons revealed that water stress during the seedling stage had a strong effect on maize growth and development,leading to lower LAI and biomass through reduced IPAR and RUE.These effects continued in the reproductive stage,thereby reducing the unit kernel weight and yield.In addition,the chlorophyll content of the leaf remained lower in plants,resulting from the water stress during the seedling stage,even when irrigation was resumed afterwards.Severe and prolonged water stress during the seedling stage may damage the structure of the photosynthetic membrane,resulting in lower chlorophyll content and RUE.In our experiments,the maize plants with such damage did not show a meaningful recovery even when the irrigation levels during the rest of the growth period were the same as those for the Full IRR treatment.Overall,these results suggest that an unrecoverable yield loss could occur if summer maize were exposed to severe and extended water stress during the seedling stage.?2?Evaluation and improvement of ceres-maize modelThis study evaluated and improved the CERES-Maize simulating the kernel weight,aboveground biomass,yield,and LAI of maize under the water stress conditions.Our results found that the model simulated those variables realistically under the full irrigation condition,while the simulations were poor under the water stress conditions,especially with the seedling stage water stress treatments.The water stress during the vegetative growth stage,especially the seedling stage,delayed the anthesis date and maturity date of maize,and extended the growth period of maize.In the original CERES-Maize model,the effects of water stress on the phenology were not considered.Such effects were added in the model to improve the maize phenology simulations for this study.In the meanwhile,CERES-Maize underestimated the leaf area and aboveground biomass due mainly to the overestimated effects of water stress on photosynthesis.We also modified the soil water conductivity coefficients used in calculating root water uptake to improve the simulations of the effects of water stress on photosynthesis.Our results show that the simulations of LAI and soil water content were more accurate with the improved model.In addition,we found that water stress during the seedling stage damaged photosynthetic membrane and reduced the chlorophyll content in the leaf based on observations.Thus,the RUE significant decreased throughout the growth period even though water stress did not occur over the later growth stages.A linearly regressed RUE factor was applied to the optimal RUE to reflect the effects of leaf structural damages without water stress.Our simulations of the LAI,aboveground biomass,yield,and soil water content were further improved by considering such a factor.?3?The effect of the decrease of sunshine hours and maximum temperature and the change of varieties on maize yieldA decline in SSH was observed across most of the meteorological stations in northern China.We found this decline to be highest in the warm season,when summer maize grows.A downward trend of-0.068 h day^-1 for SSH was observed over the seven selected crop stations in central China for the summer maize growth period of 1994-2012.A downward trend of-0.5 ^oC decade^-1 in T_max was observed for the same period,which is likely associated with the decline in SSH.The CERES-Maize model was first calibrated and validated against observed yields,and the simulations agreed very well with observations.The model was then used to quantify the effects of the declines in SSH and T_max on the maize growth period and yields,which were examined with and without the trends of these two climate forcing variables.CERES-Maize was also used to examine how cultivar replacements affected maize yields by comparing the results with and without cultivar replacement.Our modeling results indicated that the decline in SSH reduced the maize yield by 8%on average over our study stations by limiting root growth,and the decline for shorter SSH played a more important role in affecting the yield than that for longer SSH.In the meantime,the decrease in higher T_max increased the yield where the extended growth period generated a dominant effect,while the decrease in lower T_max reduced the yield where the lowered thermal time was most important.In addition,the observed yield showed a significant upward trend,which can be attributed mainly to the frequent cultivar replacements over the study period based on our modeling results.When compared with the prior cultivars,the replaced cultivars usually had a longer growth period,prolonging grain-filling time.Net maize production increased with the combined effects of cultivar replacements and the declines in SSH and T_max on yields.?4?The effects of climate change and the northward shift of maize planting area on national maize yieldChina's total maize production,yield per unit area and planted area all increased significantly from 1979 to 2015.During this period,the yield and planting area increased rapidly in north China,especially in northeast China and Xinjiang.Both growth cumulative temperature?GDD?and high temperature kill cumulative temperature?KDD?are increasing in each growth period of maize due to the continuous increase of temperature.The relationship between maize production and GDD and KDD was established using panel statistical regression model using historical data.According to the analysis,compared with the actual planting area with a north shif,the fixed planting area has less influence on GDD,and the yield trend of GDD is also similar in the two scenarios.However,KDD increased significantly in the case of fixed planting area,resulting in a decrease in national maize yield.It shows that the northward shift of maize planting area significantly reduces the KDD increase in yield at the national level and effectively alleviates the negative effect of temperature rise.The maize planting area will reach saturation by 2050?the total area of current grain planting?according to the current growth trend of maize planting area in each region.The regression model was used to predict the trend of maize yield during 2050 to2100.In each RCP scenario,the GDD trend has little impact on the yield trend.The KDD trend also has little impact on the yield trend under the scenario of RCP2.6.In the other three cases,the KDD trend caused the production to decline to varying degrees(18-102 kg ha^-1year^-1).In general,in the case of planting area saturation in future,the yield decline trend caused by the future KDD trend(-40 kg ha^-1 year^-1)is much larger than the recent value(-10kg ha^-1 year^-1)without offsetting by the planting area moving north.The scale of this study is from point to regional scale and finally point to national scale.The research content includes the main weather factors affecting crops,such as water,light and temperature,as well as the measurements were taken by people to cope with climate change.This study aims to understand and supplement the deficiencies in the knowledge system of the impacts of climate change on crop yield from different perspectives.The research results can provide theoretical basis and scientific basis for understanding and mastering the impacts of climate change on maize yield in China and provide help for various adaptation measures to cope with climate change.