Responses Of Plant Traits Under Simulated Rainfall Disturbances And Effects On Ecosystem Functions In Inner Mongolia's Typical Grassland

Grassland ecosystems are the main material support for pastoral development.They are an important barrier for protecting natural ecosystems and play a very important role in safeguarding the national food supply and ecological security.Global climate change and drought,however,have led to grassland degradation and desertification.What measures should be taken to prevent or reduce the negative impact of drought stress is an urgent issue that needs to be explored.To discuss the possible solutions and challenges,it is necessary to first clarify the response patterns and maintenance mechanisms of ecosystem functions under drought stress.At present,the study of the responses of plant traits under rainfall disturbances and the effects on ecosystem functions in Inner Mongolia typical grassland are rarely covered.This research was conducted in a typical grassland in Inner Mongolia,China,from 2004 through 2005.Through simulation and controlled experiments,the response patterns of ecosystem functions to maintain mechanisms of grassland ecosystems was analyzed. The study site is located at the Plant Institution of the Chinese Academy of Sciences in Duolun County,southern Inner Mongolia.Samples were obtained from 14 kinds of typical, common,grassland plants and 10 plant traits from among them were selected for observation in the experiments,mainly based on the methodology introduced in A Handbook of Protocols for Standardized and Easy Measurement of Plant Functional Traits Worldwide(Cornelissen et al.,2003).Simulated rainfall was 345 mm(May to August average rainfall increased by 40～50 percent) and 115 mm(May to August average rainfall reduced by 40～50%),the May to August average rainfall in 2004 and 2005.The main findings are as follows:1.By comparing and analyzing the different plant traits and ecosystem functional characteristics under three different rainfall scenarios,the results showed:(1) The response of Inner Mongolia grassland plant traits to the ecosystem is comparatively complex and not correlated with classical plant taxonomy naturalized as Legumes,Gramineae and non-Legume and non-Gramineae forbs;(2) When rainfall was reduced by 40-50%the response could be categorized into 4 plant groups according to changes in plant traits of 10 typical steppe species: Under a 115 mm rainfall scenario,they can be categorized into four groups:①(Artemisia frigida Willd.) +(Iris lactea Pallas var.chinensis Koidzumi) +(Astragalus scaberrimus Bunge) +(Agropyron cristatum(L.) Gaertner) +(Stipa krylovii Roshevitz) + (Pocockia ruthenica(L.) P.Y.Fu) +(Heteropappus altaicus(Willd.) Novopokrovsky) + (Oxytropis microphylla(Pallas) DC.);②(Cleistogenes squarrosa(Trin.) Keng) +(Poa annua L.) +(Potentilla chinensis Bunge);③(Potentilla bifurca L.) +(Potentilla acaulis L.);④(Phlomis umbrosa Turcz.).(3) Under a 345 mm rainfall scenario,they be categorized as four groups:①(Poa annua L.) +(Stipa krylovii Roshevitz) +(Iris lactea Pall.var.chinensis Koidz) +(Artemisia frigida Willd) +(Pocockia ruthenica(L.) P.Y.Fu) +(Potentilla acaulis L.) +(Potentilla bifurca L.);②(Phlomis umbrosa Turcz.) +(Astragalus scaberrimus Bunge) +(Oxytropis microphylla(Pall.) DC.) +(Potentilla chinensis B.);③(Agropyron cristatum(L.) Gaertner) +(Cleistogenes squarrosa(Trin.) Keng);④(Heteropappus altaicus(Willd.) Novopokrovsky).2.Under different scenarios,community plant traits,such as propagule mass(PM) were significantly negatively and linearly correlated with leaf nitrogen concentration(LNC),the correlation coefficient was -0.818;The specific leaf area(SLA) was negatively correlated with leaf dry matter content(LDMC) and significantly negatively correlated with stem specific density(SSD)(the correlation coefficient was respectively -0.640 and -0.735); Leaf size(LS) was correlated with leaf nitrogen concentration(LNC) and significantly negatively correlated with the first layer root mass(FLRM)(the correlation coefficient was respectively was 0.544 and -0.666);The stem specific density(SSD) was correlated with leaf dry matter content(LDMC)(the correlation was 0.570);The root specific density was correlated with first layer root mass(FLRM)(the correlation was 0.786).The aboveground biomass(ANPP) was significantly correlated with specific leaf area (SLA) and leaf nitrogen concentration(LNC).The correlation was 0.718 and 0.669.The fresh-ground biomass was positively correlated with the SLA,LNC and negatively correlated with stem specific density(SSD) and propagule mass(PM).The correlation coefficient,was respectively 0.552,0.552,-0.531 and -0.554.In terms of the 10 types of plant traits analyzed in this research,it was found that to a large extend the systematic functional characteristics of a typical Inner Mongolia grassland are determined by SLA,LNC,SSD as well as PM.The above plant traits might be those plant functional traits of Inner Mongolia grassland plants which closely related to.3.The model of multiple linear regression equation was established with variables of community plant traits and ANPP.y(ANPP)=-101.757+6.692 X1(SLA) +1.549 X2 (LNC) +0.579 X3(PH).Due to missing values for stem specific density(SSD) and propagule mass(PM),these two plant traits were not included in this model.4.The aboveground biomass obviously decreased with a reduction in rainfall while increase in rainfall had no significant impact.The sampled site was a young grassland community at an early developmental stage.The observations reveal that some species which are more adapted to normal rainfall occupy more space and thus gain a higher aboveground biomass,which explains why an increase in rainfall did not directly lead to a rise in above ground biomass.This observation revealed a rainfall-aboveground biomass model difference between young and mature communities.5.Litter decomposition rate(LR) was significantly correlated with aboveground biomass (dry weight / fresh weight) and rainfall scenarios;the correlation respectively was as 0.718,0.698 and 0.687.A higher level of rainfall can lead to a higher litter decomposition rate.It could concluded that an increase in rainfall will increase the carbon cycle and nutrient dynamic contribution in typical Inner Mongolian grassland ecosystems.