Effects Of Changing Precipitation In Different Period On Species Richness And Aboveground Net Primary Production In A Semi-arid Grassland Of Northern China

Global change strengthens hydrological cycle in the atmosphere,resulting in the shift on precipitation regimes.Given the importance of changing precipitation pattern on grassland ecosystem,ecologists have conducted many manipulative experiments,including precipitation amount,precipitation frequency and precipitation timing to examine the effects of changing precipitation patterns on grassland ecosystem structure and functions.However,the evidence that simultaneously manipulate precipitation amount and timing to explore the response of soil properties,plant functional traits,community composition,diversity,and ecosystem functions in grassland ecosystems is still rare.A manipulative experiment including control,increased/decreased 60% of mean annual precipitation in the early growing season(April-June),the late growing season(June-September)and the whole growing season(April-September)was conducted to examine the effects of altering precipitation amount and timing on soil properties,plant functional traits,community composition,diversity,and aboveground net primary production(ANPP)in a semiarid grassland in Mongolian Plateau,China.From 2015 to 2017,decreased precipitation in the early growing season had no effect on species richness or the richness of functional groups.Decreased precipitation in the late growing season significantly reduced species richness and perennial forbs(PF)richness by 18.67% and 28.53%,respectively,but had little effect on grass(GR)richness,shrubs and semishrubs(SS)richness,or annual and biennial plants(AB)richness.Decreased precipitation in the late growing season significantly suppressed PF richness through reducing late soil moisture and microbial biomass carbon,and finally led to the decline of species richness under community level.From the perspective of plant functional traits under species level,we found that species with more leaf water content would disappear faster under the treatment of decreased precipitation in the late growing season.Therefore,plant species richness decreased with the decline of the water content of the leaves,and also reduced with the increase of dry matter content and leaf area at the community level.Increased precipitation in the early growing season had no effect on species richness or richness of functional groups.Increased precipitation in the late growing season had little effect on species richness,PF richness,GR richness,or SS richness,but significantly increased AB richness by 33.90%.Increased precipitation in the late growing season significantly enhanced soil nitrogen availability and thus increased AB richness.Decreased precipitation in the early growing season declined ANPP and GR biomass by 28.88% and 53.31%,respectively,but had little effect on the biomass of SS or AB.The significant reduction of ANPP under the treatment of decreased precipitation in the early growing season primarily attributable to the suppression of GR biomass,which was suppressed by lower water availability in the early growing season.Decreased precipitation in the late growing season reduced ANPP,PF and SS biomass by 38.63%,68.37%,and 50.44%,respectively,but had little effect on GR or AB biomass.The strong decline of ANPP under decreased precipitation in the late growing season could be primarily caused by the reduction of PF and SS biomass.The PF biomass was reduced by enhancing soil temperature,whereas SS biomass was decreased with lower soil microbial biomass carbon(MBC).Neither the treatment of increased precipitation in the early growing season nor in the late growing season affected ANPP and the biomass of functional groups.These findings suggest that decreased precipitation during different periods of growing season will have larger effects on species richness and ANPP than those of increasing precipitation in this grassland,especially in the treatment of decreased precipitation in the late growing season.The study also highlight that GR was more sensitive to decreased precipitation in the early growing season than in the late growing season.By contrast,PF and SS were more sensitive to decreased precipitation in the late growing season than in the early growing season.At the species level,the result demonstrates that species with high water content in the leaves were more vulnerable to drought under the treatment of decreased precipitation in the late growing season.This study is a further improvement and extension of current report on changing precipitation patterns,and will provide strong data support for accurately predicting the response of semi-arid grassland to changing precipitation patterns under future global change scenarios.