Effects Of Seasonal Rotational Grazing On Plant Functional Traits And Diversity Of Desert Steppe

Plant functional traits and species diversity are important contents of biodiversity-ecosystem functions.In grazing ecosystems,the feeding of herbivores can change the structure of plant community species,which can also affect the functional traits and vegetation diversity of the communities.The functional traits of plants are the manifestation of plants adapting to the environment and was the result of plants adapting to the environment during evolution.The study of plant functional traits in grazing grasslands is of great significance for understanding the ecological strategies of plants adapting to the environment and formulating reasonablds for grase grazing methoslands.In the desert grassland of Yanchi County,Ningxia,the study set 4 types grazing method(with FY as control),which were including traditional time grazing(FG),delayed starting grazing(YG),early ending grazing(TG),and delayed starting early grazing(YT).Four rotation grazing methods in four areas in warm season,the characteristics of root and leaf functional traits,species diversity,and functional diversity changes of grassland plant communities under seasonal rotation grazing were studied,with which a view to provide a basis for the use of desert grasslands.The main conclusions were as follows:(1)The important value of Leymus secalinus increased,while those of Astragalus melilotoides and Convolvulus ammannii were decreased.The treatments with higher grazing frequency were significantly increased the important value of the annual biennial herb Artemisia scoparia.Grazing had no significant effects on the biomass of different functional species under each treatment.There was no significant difference between grazing and enclosure grassland in the coverage and density of community.The community coverage of TG and the community density YT were higher than that of the enclosure grassland,and YG treatment significantly reduced the community height.(2)The horizontal leaf traits of community in the FG treatment were the smallest.The TG and YG treatments significantly increased the leaf area of the community.All grazing treatments significantly reduced the leaf thickness of the community.The leaf area and leaf thickness of semi-shrubs significantly in FG treatment,and grazing significantly increased the specific leaf area of semi-shrubs.The leaf area of the biennial herb was the largest in the TG treatment,and grazing reduced the specific leaf area,leaf dry matter content and leaf thickness of the biennial herb.In each treatment,the changes of leaf dry matter content and leaf thickness were synergistic,and the plasticity index of leaf thickness is the smallest among leaf traits,which was considered as an inert index.Besides specific leaf area and dry matter content,there was a positive correlation among other leaf characters.(3)The root volume and underground biomass of grazing treatment were significantly reduced in the 30-45 cm soil layer(P<0.05),The underground biomass,root volume,root length density and root surface area density decreased with the deepening of soil layer(P<0.05),the change of specific root length was reversed.There was no significant change in root length and root surface area of different diameter grades(P>0.05).(4)Correlation analysis showed that there was a significant negative correlation between leaf area,leaf dry matter content and underground biomass(P<0.05),but no significant correlation between other leaves and characters.(5)FG treatment significantly reduced the Patrick index of the community,however YT treatment was beneficial to maintain a higher level of Patrick index.There was no significantly difference of Shannon-Wiener diversity index between grazing grassland and enclosed grassland,but the diversity index of YT grazing treatment was significantly higher than that of FG and YG treatments.The richness index FRic,which were decreased under FG and YG treatments,was the lowest under FG treatment The species diversity(Pielou and Simpson)and functional diversity(FEve,FDiv)indexes had no significant effect on grazing.Correlation analysis found that the functional richness index FRic had a extremely significant positive correlation with species diversity(Patrick,Shannon-Wiener),and had a significant positive correlation with Pielou and Simpson indexes.The functional dispersion index FDiv had a extremely significant negative correlation with Shannon-Wiener,Pielou and Simpson indexes.(6)The species richness index(Patrick)was positively correlated with dry matter content and leaf thickness of community leafs,and functional richness index(FRic)was significantly positive correlated with leaf area and leaf thickness community specific.We found that there was a extremely significant negative correlation between the functional uniformity index FEve and the above-ground biomass.(7)Entropy weight method was used to calculate the weight of the grassland community characteristics,leaf functional traits,root characteristics and vegetation diversity,we found that the diversity index had the highest weight while the leaf functional traits had the smallest weight.The comprehensive index of desert vegetation was ranked as follows:YT(0.669)>TG(0.666)>FY(0.470)>FG(0.302)>YG(0.277),of which TG and YT treatments were greater than that of FY treatment.The study suggests that desert grasslands may consider delaying the start of grazing or delaying the start of early termination of grazing.