Effect Of Silicate Supply On Rice-wheat Growth And Greenhouse Gas Emissions Under Enhanced UV-B Radiation

Global warming and stratospheric ozone depletion are two important environmental problems we are facing in recent years.The environmental problems are mainly concerned with the emissions of greenhouse gases due to human activities.Enhanced UV-B radiation induced by stratospheric ozone depletion suppressed crop growth,and decreased crop prductions.Enhanced UV-B radiation also affected greenhouse gas emissions from field soils.Rice and wheat are two staple food crops in China,while the rice-wheat rotation system also played an important role in emiting methane(CH4)and nitrous oxide(N2O).Therefore,more attentions have paied how to increase rice and wheat productions,and simultaneously reduce the emissions of greenhouse gases in this research field.In this study,field experiments were conducted to investigate the effects of silicate supply on physiological properties,growth as well as CH4 and N2O emissions in rice-wheat rotation system under enhanced UV-B radiation.This study is helpful in providing experimental findings and new measures for increasing rice and wheat productions,and reducing the emissions of greenhouse gases under enhanced UV-B radiation.Main results are listed as below:(1)Physiological properties in rice and wheatEnhanced UV-B radiation inhibited the photosynthesis and transpiration of rice and wheat.However,silicate supply could promote the photosynthesis in rice and wheat,then improve water use efficiency in wheat and effectively alleviate the inhibitory effect of enhanced UV-B radiation.Enhanced UV-B radiation could significantly decrease net photosynthetic rate,stomatal conductivity,stomatal limitation and transpiration rate,and meanwhile increase intercellular CO2 concentration and water use efficiency in rice.Enhanced UV-B radiation could significantly decrease net photosynthetic rate,stomatal conductivity,intercellular CO2 concentration and transpiration rate,and increase stomatal limitation and water use efficiency in wheat.Silicate supply could significantly increase net photosynthetic rate,stomatal conductivity,stomatal limitation and transpiration rate,and decrease intercellular CO2 concentration,and had no significant effect on water use efficiency in rice.Silicate supply could significantly increase net photosynthetic rate,stomatal limitation and water use efficiency,and decrease stomatal conductivity,intercellular CO2 concentration and transpiration rate in wheat.(2)Growths and yields of rice and wheatEnhanced UV-B increased leaf area index,the dry matter weights of shoot and root,inhibited the growth and development of rice and wheat,and reduced yield component factors(grain number per spike and thousand-grain weight),finally decreased rice yield by 4.30%-9.36%and wheat yield by 9.08%-22.61%.Silicate supply could significantly increase leaf area index,the shoot and root dry matter weights,promote growth and development in rice and wheat and reduce the adverse effects of UV-B enhancement.Rice yield was increased by 14.01%-20.37%,and wheat yield increased by 4.83%-23.15%.(3)CH4 and N2O emissions from rice and wheat field soilsSilicate supply did not change the seasonal trend of CH4 and N2O emissions from rice and wheat field soils under enhanced UV-B radiation.Enhanced UV-B radiation significantly increased CH4 and N2O fluxes and accumulated emissions in rice and wheat soils,whereas silicate supply significantly reduced CH4 emissions,but increased N2O emissions.Therefore,the global warming potential(GWPs)is used to elucidate whether silicate supply could reduce the combined greenhouse effects of CH4 and N2O emissions.The results showed that enhanced UV-B radiation stimulated the GWPs of CH4 and N2O emissions,while silicate supply significantly reduced the GWPs of rice soil,but increased the GWPs of wheat soil.During the whole rice-wheat growing period,silicate supply significantly reduced the contribution of enhanced UV-B radiation to global warming potentials.