| Guangxi is the largest sugarcane planting area in China,the increase and decrease of its production and the quality affect the livelihood of the people.Many studies shown that climate change will continue to exist in the future,and will have some significant impacts on sugarcane productivity.Therefore,it is of great scientific significance to clear the climate change rules in Guangxi and analyze the influence on sugarcane productivity.In this paper,selecting the field experiment data,meteorological data,sugarcane parameters and soil parameters from several study sites in Guangxi,to calibrate and validate the APSIM-sugarcane model.Then combining with the global climate model(GCM),modeling the sugarcane growth and development under future climate conditions in Guangxi,and analyzed the changes in above-ground biomass dry matter,stalk fresh matter and sucrose dry matter in three future periods(2030s:2021-2040,2060s:2051-2070 and 2090s:2081-2100)compared to the baseline period(1961-2010).In additional,exploring the changes in temperature,rainfall and radiation in three future periods(2030s:2021-2040,2060s:2051-2070 and 2090s:2081-2100)compared to the baseline period(1961-2010)in Guangxi,to discuss the relationship between the changes in sugarcane productivity changes and climate changes.The main conclusions are as follows:(1).APSIM-sugarcane calibration and validationIn this paper,selecting the field experiment data from planting on February 2015 in Nanning site to calibrate the APSIM-sugarcane model,the field experiment data from planting on March and April 2015 in Nanning and some field experiment data from another study sites(Laibin,Shatang,Pingguo,Guigang and Hechi)in Guangxi to validate the APSIM-sugarcane.After the calibration and validation,the APSIM-sugarcane presented a good performance on sugarcane growth and productivity.The sugarcane development simulations indicated that the emergence simulations were better than the cane appearance simulations(R2 were 0.95 and 0.89 for emergence day and cane appearance day,respectively;and RMSE were 11d and 23d for emergence day and cane appearance day,respectively.).From sugarcane production simulations,we found that the best simulations were for sucrose dry matter(R2 was 0.93 and RMSE was 0.88t·ha-1);following were stalk fresh matter simulations(R2 was 0.82 and RMSE was 18.89t·ha-1).However,the leaf area index(LAI)simulations were weaker than other indicators(R2 was 0.70 and RMSE was 1.07m2·m-2).Some validations from another study sites in Guangxi indicated that APSIM-sugarcane predicted the stalk fresh matter well(R2 was 0.78 and RMSE was 7.87 t·ha-1).In a word,APSIM-sugarcane model can effectively have applied to the simulation of sugarcane growth and productivity in Guangxi.(2).Evaluation and Differential Analysis of GCMs Climate DataThe evaluation of 28 GCMs climate data under the RCP4.5 and RCP8.5 showed that the global climate model has better simulation in temperature than rainfall and radiation in Guangxi,and the GCMs temperature data is more discrete than rainfall and radiation.The results of the variability analysis of Guangxi modeling climate data from the global climate model show that,the coefficients of variation of temperature,rainfall,and radiation under RCP 4.5 were smaller than that under the RCP8.5 scenario at the same stage,under the similar emission scenarios,the coefficient of variation of temperature was very small from 2030s to 2090s,however the coefficients of variation of rainfall and radiation were increased with time.(3).Temporal and spatial variability of climate and sugarcane productivity in the futureThe study calculated the average value of 28 GCMs climate data found that changes in future temperature,rainfall and radiation all increased under different greenhouse gas emission patterns.The increase of the daily average temperature at 22 study sites under the RCP 4.5 was smaller than that under the RCP8.5 in Guangxi.The changes in rainfall and radiation were irregular in the two different RCPs,but all showed increase in 2060s and 2090s compared to 2030s.The changes during the 2060s and 2090s periods were inconsistent,most sites increased gradually,and some sites were consistent in two phases.The changes in above-ground biomass dry matter,stalk fresh matter and sucrose dry matter showed an increasing trend year by year under different greenhouse gas emission patterns,and the changes in above-group biomass dry matter and stalk fresh matter were similar.Most study sites showed greater increase in yield under the RCP4.5 scenario than that under the RCP8.5 scenario at the same period.The yield for all sites increased from 2030s to 2060s,while the increase in yield was similar in most of the sites during 2060s and 2090s,and the increase in yield decreased in a few sites for 2090s.(4).Quantifying the impact of climate changes on yield changesThrough regression analysis of changes in climate and sugarcane yields,there was no significant correlation between changes in sugarcane biomass(aboveground biomass dry matter and stalk fresh weight)and radiation changes.There was little correlation with CO2 concentration,which may be since sugarcane was a C4 plant.Therefore,CO2 concentration has little effect on sugarcane growth.A significant positive correlation with rainfall and temperature was showed.From the Tylor diagram of temperature,rainfall,and biomass(aboveground biomass dry matter and stalk fresh weight)shows that rainfall has a greater impact on biomass.The increase in yield is small when the rainfall does not change and the temperature increases,and the increase in yield is significant when the temperature does not change and the rainfall increases,but the impact of rainfall on yield increase is limited.The continuous increase in rainfall will cause the decrease in yield When the increase in rainfall reaches a certain limit,especially in areas with weaker radiation increase.In addition,temperature,rainfall,and radiation all have a significant positive correlation with sucrose yield.The synergy of temperature and rainfall has similar effects on the yield and biomass of sucrose.The positive correlation between temperature and radiation synergy on sucrose yield needs to be established under rich soil moisture conditions.Under the conditions of rich rainfall,the increase of radiation increases plays a big role in increasing sucrose yield.However,similarly,if the radiation increase exceeds a certain limit,the increase of radiation will result in decrease the yield,while sucrose yield will increase in areas where rainfall and radiation increase are more significant.(5).Analysis of differences between irrigation and rainfall yieldBased on the APSIM-sugarcane,we set up irrigation modeling experiments and found that soil moisture plays an important role in sugarcane yield.In the context that the temperature in each study period gradually increases and the temperature at 22 study sites increases similarly in the future,the set of automatic irrigation in sites where there is less rainfall and less rainfall increase in the future can increase the soil moisture contents,thereby bringing significant increase in sugarcane yield((above-ground biomass,stalk fresh matter and sucrose dry matter),especially for sucrose yield.In sites where radiation increases significant in the future,sucrose yield increases significantly when the soil water contents are always sufficient after irrigation,while in areas with more rainfall,due to the large base of soil moisture,the effect of irrigation on the increase of sugarcane yield is relatively small. |
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