Relationships Between Plant Functional Group Diversity And Soil Carbon And Nitrogen Storages Under Different Rainfall Zones

Global change in biodiversity loss is threatening ecosystem functioning and services,i.e.,carbon and nitrogen cycle,productivity,and the carrying capacity of plants and animals.Different species diversity tends to influence different ecosystem processes,so studies focusing solely on the number of species will underestimate the level of biodiversity required for ecosystem multifunctionality.As an important component of plant diversity,functional group diversity is crucial for maintaining the stability of grassland ecosystem functioning,resisting invasion and buffering the negative effects of climate change.As far,from the perspective of plant functional groups,studies on the responses of carbon and nitrogen storage in grassland ecosystems to climate change have focused on small spatial scales or control experiments with functional group removal.That is changes in functional groups and species diversity are caused by anthropogenic community changes.Although these studies have improved the theoretical knowledge of the role of functional group diversity in carbon and nitrogen cycles in grassland ecosystem,the understanding of the relationship between functional group diversity and carbon and nitrogen storages in natural grassland ecosystems is still limited.Taking natural grassland ecosystem in Gansu Province as the research object,our study systematically studied the distribution characteristics of plant functional group diversity and soil carbon and nitrogen storages in grassland communities under different rainfall zones through field experiments,laboratory analysis,and data statistics,and analyzed the relationships between plant functional group diversity and soil carbon and nitrogen storages in grassland communities.The main conclusions were as follows:（1）The functional group richness and evenness of forbs,grasses,sedges,and legumes in 400-800 mm rainfall zone were significantly higher than those in<200 mm and 200-400mm rainfall zone.Compared with the 400-800 mm rainfall zone,the forbs functional group richness in>800 mm rainfall zone increased significantly by 21.97%,and the grasses and legumes functional group richness in>800 mm rainfall zone decreased by 25.55%and39.08%,respectively.The forbs functional group richness and evenness were the highest in the different plant functional group-dominated grassland communities,including the forbs,grasses,sedges,and legumes functional groups-dominated grassland communities.The forbs functional group richness in all rainfall zones was the highest in forbs plant functional group-dominated grassland communities,but the forbs functional group evenness was the highest in the sedge-dominated grassland communities in the<200 mm rainfall zone,and was the highest in the legumes-dominated grassland communities in 200-400 mm and400-800 mm rainfall zones.（2）Soil organic carbon storage（SOCs）and total nitrogen storage（TNs）both firstly increased and then decreased across all rainfall zones,and reached the peak values of 84.79Mg hm^-2 and 8.18 Mg hm^-2 in 400-800 mm rainfall zone,respectively.SOCs and TNs were significantly higher in the sedge-dominated grassland communities than in other plant functional group-dominated grassland communities,but there were differences in the SOCs and TNs in plant functional group-dominated grassland communities under different rainfall zones.SOCs and TNs were the highest in the sedge-dominated grassland communities in<200 mm and 400-800 mm rainfall zones,while they were the highest in the legumes-dominated grassland communities in 200-400 mm rainfall zones.In>800 mm rainfall zone,SOCs and TNs were higher in the forbs-dominated grassland communities than in the grasses-dominated grassland communities.The 10-20 cm soil layer of plant functional group-dominated grassland communities under different rainfall zones had the largest SOCs and TNs.（3）The increased functional group diversity all significantly increased SOCs and TNs,and the forbs functional group diversity was the main factor affecting the SOCs and TNs.The higher sedges functional group diversity,the higher SOCs and TNs.In forbs-and grasses-dominated grassland communities,the SOCs and TNs were more sensitive to the sedges and legumes functional group diversity.In sedges-dominated grassland communities,only the forbs and legumes functional groups diversity was significantly positively correlated with SOCs and TNs.In the legumes-dominated grassland communities,only the forbs functional group diversity had a significant correlation with SOCs and TNs.The effects of climate on the carbon and nitrogen storages of grassland ecosystem were regulated by the functional group diversity within the grassland community.Among the changes in the community functional group diversity caused by changes in rainfall,the forbs functional groups dominate the community,which may be due to the high diversity of forbs functional group.Further,the forbs functional group diversity（especially evenness）might be stronger than that of grasses,sedges,and legumes in mitigating and adapting to climate change.Therefore,it is necessary to consider the changes in plant functional groups when accurately assessing the impact of climate change on the natural grassland ecosystem functioning.Long-term studies on the relationships between functional group diversity and soil carbon and nitrogen dynamics should be strengthened,in order to provide scientific basis for better predicting the trend of carbon and nitrogen storages in grassland ecosystem and the role of functional group diversity in grassland communities under future climate change and human activities.