Effects Of Elevated CO₂ Concentration,Warming And Mild Drought On Soil Water-soluble Components And Thermodynamic Characteristics Of Enzymes In Winter Wheat

The impact of climate warming and drying on agricultural production has attracted more and more attention.Winter wheat is one of the main food crops in our country,therefore,it is necessary to clarify the effects of the elevated CO₂ concentration,warming,mild drought stress and their interactions on soil carbon,nitrogen and phosphorus cycle of winter wheat,which is of great significance to the implementation of farmland production and management strategies under climate warming and drying in the future.Previous studies have made some progress,but most of them just focused on the influence of single climatic factor and ignored the interactions of multiple climatic factors.In view of this,soil from a C₃ crop,winter wheat（Triticum aestivum L.）,was selected as the research object to carry out pot experiment in this study.Four climate scenarios were designed based on the artificial climate chamber,which were current atmospheric CO₂ concentration and current ambient temperature（CK）,elevated CO₂ concentration（EC）,elevated temperature（ET）,elevated CO₂ concentration and elevated temperature（EC+ET）.In addition,two moisture conditions were set in this study,full water supply（80%field capacity）and mild drought stress（60%field capacity）respectively.The purpose of this study was to investigate the effects of elevated CO₂ concentration,warming,mild drought stress and their interactions on soil water-soluble component（DOC,WSN and WSP）contents and their stoichiometric characteristics and the temperature sensitivity of 7 soil hydrolase activities(Q₁₀)related to C,N and P cycles at four growth stages（jointing stage,flowering stage,filling stage and mature stage）of winter wheat.The main results are as follows:（1）The responses of different soil water-soluble component contents to the elevated CO₂ concentration,warming,mild drought stress and their interactions were different.Specifically,both elevated CO₂ concentration and warming significantly decreased soil DOC content,while mild drought stress significantly decreased soil DOC content at reproductive growth stage of winter wheat;The elevated CO₂ concentration increased soil WSN content,but the effect was not significant,while warming and mild drought stress significantly increased soil WSN content;The elevated CO₂ concentration significantly reduced soil WSP content,while warming and mild drought stress only significantly reduced soil WSP content at jointing stage of winter wheat.Besides,the interactions of the two climatic factors and the three climatic factors showed superposition effects on the decrease of soil DOC content and the increase of soil WSN content.The interaction between growth period and mild drought stress significantly affected soil DOC content.The aboveground biomass and underground biomass of winter wheat were the main factors affecting the soil water-soluble component contents.（2）Various climatic factors（the elevated CO₂ concentration,warming and mild drought stress）and their interactions had certain effects on stoichiometric characteristics of soil water-soluble components.Specifically,the elevated CO₂ concentration,warming and mild drought stress significantly reduced soil DOC:WSN;The elevated CO₂ concentration and mild drought stress significantly increased soil DOC:WSP and soil WSN:WSP respectively;Warming increased soil WSN:WSP,but the effect was not significant;Besides,the interactions of the two climatic factors and the three climatic factors showed superposition effects on the decrease of soil DOC:WSN;The interaction between warming and mild drought stress showed a superposition effect on the increase of soil WSN:WSP.The interaction between growth period and warming as well as the interaction between growth period and mild drought stress had significant effects on soil DOC:WSP,and the interaction between growth period and the elevated CO₂ concentration had a significant effect on soil WSN:WSP.The aboveground biomass and underground biomass of winter wheat were the main factors affecting the stoichiometric characteristics of soil water-soluble components.（3）The responses of Q₁₀ of hydrolases associated with soil C,N and P cycle to various climatic factors（the elevated CO₂ concentration,warming and mild drought stress）and their interactions varied with the growth stage of winter wheat and enzyme type.Specifically,both the elevated CO₂ concentration and warming significantly reduced Q₁₀ of hydrolases associated with soil C cycle,while the effect of mild drought stress on Q₁₀ of hydrolases associated with soil C cycle varied with the enzyme type;The elevated CO₂concentration significantly increased Q₁₀ of hydrolases associated with soil N cycle,and the effect of warming on Q₁₀ of hydrolases associated with soil N cycle varied with the growth stage of winter wheat and enzyme type.Mild drought stress significantly decreased Q₁₀ of hydrolases associated with soil N cycle in early growth stage of winter wheat and significantly increased Q₁₀ of hydrolases associated with soil N cycle in mature stage of winter wheat;The elevated CO₂ concentration significantly increased Q₁₀ of hydrolase associated with soil P cycle,and the effect of warming on Q₁₀ of hydrolase associated with soil P cycle varied with growth stage of winter wheat.Mild drought stress significantly reduced Q₁₀ of hydrolase associated with soil P cycle.Besides,the interaction of the elevated CO₂ concentration and warming showed a superposition effect on the decrease of Q₁₀ of hydrolases associated with soil C cycle,and the reduction of Q₁₀ of hydrolase associated with soil P cycle induced by mild drought stress could be offset by the elevated CO₂ concentration.The aboveground biomass of winter wheat,soil WSN and nitrate nitrogen were the main factors affecting Q₁₀ of hydrolases associated with soil C、N and P cycle.The above research results showed that the effects of elevated CO₂ concentration,warming,mild drought stress and their interactions on soil water-soluble components and Q₁₀ of hydrolases associated with soil C、N and P cycle varied with growth stage of winter wheat.At the same time,the responses of various soil water-soluble components and Q₁₀ of hydrolases associated with soil C、N and P cycle to various climatic factors and their interactions were also different at the same growth period.The elevated CO₂ concentration,warming,mild drought stress and their interactions do not simply promote or inhibit the cycling of soil carbon,nitrogen and phosphorus,which involves the influences of growth and development of crops,soil nutrients and soil microorganism activities.