Effects Of Long-term Removal Of Plant Functional Groups In Sub-alpine Meadows On Plant And Soil Properties

Grassland ecosystems are facing species loss and serious ecological function degradation due to global climate change and human activities.However,it is not clear how the loss of biodiversity in grassland communities affects ecosystem functioning processes.Current biodiversity loss experiments have focused on studies of aboveground plant community-related responses,with relatively little attention paid to belowground soil processes.In our study,a 9-year different plant functional groups removal experiment was conducted in a sub-alpine meadow on the eastern edge of Qinghai Tibet Plateau.By removing all plants,forbs,gramineous group and leguminous group respectively,the effects of long-term loss of plant functional groups on the main processes and functions of the aboveground and underground ecosystems of the subalpine meadow ecosystem and its response mechanism were studied.The main results are as follows:1.The plant communities retained in subalpine meadows have different compensatory effects on the removal of different plant functional groups.The removal of gramineous group significantly reduced the aboveground plant biomass,and the remaining species could not compensate for the biomass loss caused by the loss of gramineous group,showing the weakest compensation effect.After the removal of forbs and legumes,the remaining species can compensate for the biomass loss caused by their loss,and the compensation level was close to the equal compensation.This suggests that graminoids,as the dominant species,largely determine aboveground biomass,supporting the mass ratio hypothesis.2.The removal of different plant functional groups also had a significant effect on the community diversity index.Species richness,Shannon-Wiener diversity index,Simpson diversity index and Pielou evenness decreased significantly after the removal of forbs due to the high number of forbs in the community,while Pielou evenness increased significantly after the removal of graminoids.This showed that although the functional group of forbs cannot compensate for the loss of biomass caused by species removal,it can compensate for the loss of species number.The removal of dominant gramineous group can improve the level of plant diversity to a certain extent,which indicated that there is a certain degree of competition between gramineous group and other subordinate species.3.The long-term removal of plant functional groups had little effect on soil properties.Compared with the control treatment,all three removal treatments had no significant effects on soil properties,except for the removal of all plants,which significantly reduced soil water content,organic carbon,nitrate nitrogen,available nitrogen,and microbial biomass carbon and nitrogen contents.Also,except for soil water content,the differences in soil properties caused by the removal of all plants mentioned above occurred only in the top 0～10 cm of soil,and there were no significant differences in soil properties between the removal treatments at 10～20 cm soil depth.4.Structural equation modeling suggests that removal of plant functional groups negatively affects plant species richness,while species richness has a direct positive effect on soil water content,organic carbon,soluble organic nitrogen,and microbial mass carbon,which in turn indirectly affects soil carbon mineralization rates.At the beginning of carbon mineralization(day 1),soluble organic nitrogen has a direct positive effect on carbon mineralization rate,while soil water content has an indirect effect on soil carbon mineralization rate through a direct positive effect on soluble organic nitrogen;at the end of carbon mineralization(day 32),carbon mineralization rate is directly and positively influenced by water content.It can be seen that the variation in soil water content is the dominant factor in the difference in carbon mineralization rate of soils with different removal treatments.