Effects And Related Mechanisms Of Plant Functional Group Removal On Alpine Meadow Ecosystem Functioning

The potential consequences of community biodiversity loss for ecosystem processes and functioning have aroused widespread concern.With the disturbance,species loss in the natural community usually occurs in a non-random patterns,and the impact on ecosystem functioning was often depended on all species in the community.Affected by anthropogenic activities and climate change,grassland ecosystem was threatened with serious degradation and species loss.Among them,the loss of dominant species caused by over grazing of livestock are common.Based on these backgrounds,we conducted a removal experiment in alpine meadow on the east edge of Qinghai-Tibet plateau with plant functional group?PFG?.The object was to analysis the effect of PFG lost to ecosystem structure and functioning,also the relationship between PFG identity and biodiversity and ecosystem functioning,based on the monitoring of PFG composition,community structure and productivity,nutrient element content and CO₂exchange.We did the removal treatment in two consecutive growing seasons and monitoring the plant community characteristics,biomass and nutrient element characteristics and carbon flux,the main conclusions from this study are as follows:?1?The weighted average height and cumulative coverage of alpine meadow communities are mainly affected by Forb group.The removal of PFG and random biomass significantly inhibited the increase of community height,Grass coverage and SDR,also the decrease of Forb coverage and SDR,and there was no significant difference between the two removal treatments.The height and SDR of Sedge group were significantly increased when Grass was removed.The relative difference?RD?of SDR of Grass,Sedge and Forb groups all have significantly negative correlation,indicating that the coexistence of the three PFGs is being competitive to some extent.?2?Removal treatment had a significant impact on the RD of community and Grass species diversity index.The removal of Grass resulted in the increase of PFG Shannon-Wiener diversity in community and the decrease of dominance index,while the other treatments had the opposite effect.The change of SDR of Grass,Sedge and Forb could explain the variance of the change in diversity.The increase of Grass SDR significantly increased species dominance,but decreased species Shannon-Wiener diversity and evenness.The opposite was true for Forb dominance index.The increase of SDR of Grass and Forb would decrease the PFG Shannon-Wiener diversity and increase the dominance index,while that of Sedge was on the contrary.?3?Removal of PFG and random biomass only significantly inhibited the increase trend of community AGB,LB and Grass biomass,and there was no significant difference between the two removal treatments.LB decreased linearly with the increase of removed PFG and random biomass.AGB mainly depends on Grass and Forb biomass,while RB mainly depends on Sedge biomass.There was an extremely significant linear negative correlation between biomass percentage of Grass,Sedge and Forb,which further indicated that there was a competitive relationship between them and Forb.?4?There was a significant linear negative correlation between AGB and the evenness index of species in community,while there was no significant linear correlation between AGB and the other diversity index from species or PFG,indicating that the dominant Grass and Sedge group had a greater impact on community AGB.?5?Removal treatment significantly affected the nitrogen content of root,significantly reduced the carbon content and C:N of litters,but had no significant influence on the content and stoichiometric ratio of other nutrient elements.There was significant correlation between plant nutrient element content and biomass percentage of PFG in the community.The removal of functional groups significantly reduced the TN content in the soil,but had no significant influence on the RD of TC,TP content and their stoichiometric ratio.There were significant correlations between nutrient element content and stoichiometric ratio in soil and species diversity indices and PFG biomass percentage.?6?The CO₂ exchange capacity of alpine meadow ecosystem in the growing season in daytime is a net absorption,making thenm a carbon sink.The CO₂ flux of GEP,ER and NEE reached its peak in July,June and August of the growing season respectively.The continuous removal treatment of PFG significantly reduced the CO₂ absorption flux of GEP and NEE,and significantly reduced the ER in the later growing season.In the growing season of alpine meadow ecosystem,there was a significant positive linear regression relationship between CO₂ flux in GEP and ER and surface soil temperature,and a significant negative linear regression relationship between CO₂ flux in GEP and ER and surface soil water content,but there was no significant linear regression relationship between NEE and soil temperature and water content.There was a significant negative linear correlation between ER and the weighted-average height of community and species richness in July,while there was also a significant linear negative correlation between the CO₂ absorption flux of GEP and the biomass percentage of Sedge group.?7?The competitive relationships between different PFG in the alpine meadow community significantly affect the response of the community composition under various disturbances,and as the combination of similar species,combination of PFGs could significantly influence the diversity,productivity,content and stoichiometric ratio of nutrient elements,and CO₂exchange in alpine meadow ecosystem.Compared to the species richness,the impact of species identity on ecosystem processes and functioning also exists.