Plant-soil Feedback And Its Response To Nitrogen Enrichment And Warming In A Tibetan Alpine Meadow

Plant-soil feedback(PSF)is a process that plants impact soil physiochemical properties and soil biota by root exudates and litter input,and these changes in soil can in turn exert either positive or negative effects on plant performance.PSF is known to play a crucial role in maintaining plant species diversity,shaping patterns of plant relative abundance,and driving plant population dynamics.However,few studies have tested the relative importance of soil biota(e.g.,mutualist,enemy)and other abiotic factors(e.g.,nutrient,secondary metabolite)on conspecific and heterospecific PSF,and also the heterospecific PSF among different functional groups(e.g.,graminoids vs.forbs)and species with different dominance and relatedness.The interactions between soil and plants have great potential in influencing the plant-competitive and facilitative interactions but were rarely tested in alpine ecosystems.Moreover,few studies have tested how PSF depends on environmental context and whether shifts in plant community composition caused by the environmental change are associated with variation in PSF.Tibetan alpine meadow possesses extremely high biodiversity and plays a very important role in the global conservation of alpine biodiversity.In addition,Tibetan Plateau is one of the areas mostly sensitive to global change(e.g.,nitrogen enrichment and warming).Here,we explored if the interactions between alpine plants and soil will influence plants' performance and their interactions,and if the changes in PSF will influence plant community composition,especially under nitrogen enrichment and warming.We first conducted a greenhouse experiment to test the conspecific PSF and heterospecific PSF for 16 focal species and 8 soil conditioning species,that co-occurred in a Tibetan alpine meadow,with live(with soil biota)or sterile(without soil biota)soil inocula from the same site.Secondly,we conducted another greenhouse experiment to test the net effects of soil biota on the growth of 11 plant species(absolute PSF)under N enrichment and/or warming.Feedback effects were analyzed among different functional groups and species with diverse dominance and relatedness.Then we investigated the relative abundance of these 11 species in a field experiment comprising the same factorial combination of N enrichment and warming.Finally,we examined whether the changes in PSF under N enrichment and warming were related to the variation in plant relative abundance in the field.The main results are as follows:1)The net effect of soil biota on PSF in the alpine meadow was mainly negative,and the negative soil biota effect was stronger in conspecific PSF.Compared with graminoids,forbs suffered more negative PSF from the soil biota conditioned by the same species and same functional group.2)We found that the strength of negative PSF between focal species and soil conditioning species was most negative for conspecific,then congener,and lowest for confamilial.However,the similarity of plant species response to soil biota was not associated with species relatedness.3)Plant relative abundance was negatively correlated with the absolute PSF strength(R2=0.25,p=0.065)indicating that dominant species suffered more from negative conspecific soil biota.However,we did not find any significant relationship between PSF and plant relative abundance under warming and N enrichment.4)N enrichment reduced the negative PSF for both of the functional groups and most species;the warming effect on PSF varied among species;their interactive effect on PSF was significant at species and functional group levels.Most importantly,we found that the change in PSF caused by N enrichment and warming was positively correlated with the change in species abundance under N enrichment and warming in the field(N enrichment,R2=0.41,p=0.006;Warming,R2=0.33,p=0.016).Our findings indicate that the interaction between soil biota and plants may play an important role in promoting species coexistence.More specifically,the most dominant species suppressed by soil biota.In addition,conspecific PSF was more negative than heterospecific PSF,and feedback within the same functional groups(for forbs)was more negative than feedback among functional groups.Taken together,our study emphasizes the importance of PSF in predicting the change of plant relative abundance under global change.The current study also highlights the necessity to integrate the plant-soil interaction into models of plant community assembly in a changing word.