Relationship Between Plant Community Diversity And Productivity In Desert Steppe Under Controlled Precipitation

The relationship between biodiversity and ecosystem function has been one of the hot topics in ecology.Ecosystem can provide human beings with a variety of services such as material basis and living environment.As an important factor of controlling ecosystem stability,productivity,carbon sequestration,nutrient cycle and other functions and processes,biodiversity plays an important role in the realization of ecosystem functional services.Since the industrial revolution,it is an indisputable fact that the intensification of human activities has changed the global precipitation pattern.The change of precipitation pattern will affect plant growth and community diversity,and ultimately have influence on the structure and function of ecosystem.The desert grasslands of the western Loess Plateau are characterized by scarce precipitation,sparse vegetation and fragile ecosystems,and are highly sensitive to changes in precipitation patterns.Therefore,researching the relationship between plant community diversity and ecosystem function under precipitation change is of great significance for the maintenance and scientific management of ecosystem service function in this region.Based on the field precipitation control test platform of desert grassland in the west of the Loess Plateau,according to the precipitation variability of the study area in recent50 years(-41.1%-39.2%),five precipitation gradients(40%precipitation reduction,20%precipitation reduction,control,20%rainfall increase and 40%rainfall increase)are set to simulate the possible precipitation changes in the future.Through the field investigation and laboratory analysis of plant communities and plant functional traits,the data of species diversity,functional diversity and productivity were obtained to explore the relationship between plant community species diversity,functional diversity and functional traits and community productivity under the background of precipitation change.The main results are as follows:(1)The change of precipitation had a significant effect on aboveground biomass The aboveground biomass of the precipitation-reduced group was significantly lower than that of the control and rainfall-increased groups(P<0.05).The aboveground biomass of grasses in the 40%precipitation-reduced group was significantly lower than that in the rainfall-increased group(P<0.05),and that of forbs in the 40%rainfall-increased group was significantly higher than that in the remaining groups(P<0.05).The 40%precipitation-reduced treatment significantly decreased the importance value of grasses(P<0.05).To sum up,the negative effect of precipitation-reduced treatment on above-ground biomass was significant,and extreme rainfall increase and precipitation reduction had a greater effect on community composition.(2)The effect of precipitation treatment on species richness was significant,with the 40%precipitation reduction group being significantly lower than the 40%rainfall increase group(P<0.05),and the control and rainfall increase groups being significantly higher than the precipitation reduction groups,indicating that precipitation reduction reduced the number of species in the plant community,making species richness lower.(3)The effect of precipitation treatment on plant height and leaf thickness(LT)was significantly higher in the 20%rainfall-increased group than that in the precipitation reduction group(P<0.05),and in leaf thickness,the 40%precipitation-reduced group was significantly higher than the other treatment groups(P<0.05).The effect of precipitation treatment on the functional richness(FRic)of the community was significantly higher in the rainfall-increased group than in the control and precipitation-reduced groups(P<0.05);the functional evenness index(FEve)in the rainfall-increased group was significantly lower than that in the control and precipitation-reduced groups,and was significantly higher in the precipitation-reduced20%group than in the control and precipitation-reduced 20%groups(P<0.05).(4)The Pielou evenness index had a significantly negative correlation(P<0.05)with the functional richness index(FRic)and had a significantly positive correlation(P<0.05)with the functional evenness index(FEve);these species diversity indices had strong explanatory power for both the functional dispersion index(FDis),i.e.,the Simpson index,the Shannon index and the Pielou evenness index all had a highly significant positive correlation with the functional dispersion index(P<0.01).(5)The optimal indicator model for species diversity contains species richness and Pielou evenness index,which can explain 51.3%of the variation in aboveground biomass,with species richness being the dominant factor;plant functional traits have strong explanatory power for community productivity,and the specific leaf area(SLA)was the most important indicator,and the optimal indicator model contained SLACWM and LTCWM,which could explain 77.3%of the variation in aboveground biomass;the functional diversity index had weak explanatory power for aboveground biomass(R~2=0.304);the optimal indicator model of diversity and productivity was screened by multiple stepwise regression analysis.The optimal indicator model of diversity and productivity(R~2=0.863)was screened by multivariate stepwise regression analysis,containing SLACWM,LTCWM and Pielou’s evenness index,indicating that functional traits(CWM)were strong indicators of productivity,i.e.,the dominant factors of community productivity were the functional traits of dominant species,suggesting that selection effect was the maintenance mechanism of productivity of desert grassland in the background of precipitation change.To sum up,in the desert grassland in the west of the Loess Plateau,the aboveground biomass of the group is greatly affected by the extremely precipitation-reduced treatment.As the best indicator of community productivity,the functional traits of dominant species are of great value for the prediction and evaluation of desert grassland ecosystem productivity under the background of the change of global precipitation pattern in the future.Strengthening the scientific management of dominant species is of great significance to maintain the productivity of desert grassland ecosystem.