Influences Of Soil Microbial Diversity On Soil Ecosystem Function Of Qinghai-tibetan Plateau

Qinghai-Tibetan plateau is a sensitive hot spot to global climate change.Understanding the relationship between microbial community and ecosystem function would help predict the ecosystem changes under the global change and future ecosystem management.This study combined long-term fertilizaitn field experiment and short-term dilution-to-extinction method to set up soil microbial diversity gradients,and to elucidate the relations among fertilization management,soil microbial diversity and ecosystem functions(e.g.,plant productivity and litter decomposition).Our results showed that:(1)Soil suspension of a gradient of diversity was inoculated into sterile soil to build soil microbial diversity and have been incubated for 8 months.Regardless of chemical N and P fertilization or not,soil microbial diversity and richness,soil EC,DON and NH4+-N decreased while soil pH,DOC and NO3--N increased with increasing dilution levels(i.e.diversity decreased).With the increase of dilution level,microbial genotypic(16S rRNA),phenotypic(phospholipid fatty acids),functional diversity(microbial carbon source utilization)generally declined.Fertlization increased microbial genotypic diversity,but decreased phenotypic and functional diversity.Mineralization of soil organic carbon as indicated by accumulated CO2 decreased with microbial diversity.Principle component analysis(PCA)indicated the shift of soil functions measured through soil CNP acquisition enzyme activities and Biolog Eco sole substrate utilization potential at high dilution level of 10-7 and 10-8(g g-1).Together,functional parameters including soil organic carbon mineralization,enzyme activities and organic substrate utilization potential indicated high microbial diversity would be of pivotal importance for soil ecosystem service dilivery.(2)The relationship between the soil microbial diversity and plant productivity(represented by dominant species of Elynus nutans Griseb)showed that microbial diversity derived from fertilization treatment was positively correlated with plant(shoot and root)biomass(R2 = 0.96,P<0.01)and plant total N uptake(R2 = 0.87,P<0.05)and K(R2 = 0.96,P<0.01)and shoot biomass(R2 = 0.95,P<0.01)if soil microbial community was from no fertilizer treatment.Without the influence of fertilization,microbial diversity showed unimodal relationship with root biomass(R2 = 0.95,P<0.01),plant total absorption for N(R2= 0.96,P<0.05),shoot N uptake(R2= 0.96,P<0.05),root K uptake(R2= 0.89,P<0.01),which implied microbial diversity and plant biomass and nutrient uptake was co-dependent in terms of resource competition.RDA analysis showed that,without fertilization,the competition between roots and microorganisms contributed to the decrease of soil nutrient availability,but the higher DON release might partly compensate for nutrient limitations for plant growth.(3)The relationship between the soil microbial diversity and organic matter decomposition showed that heating stress significantly increased the concentrations of DOC and DON.With decresing microbial diversity,DOC significantly increased regardless of fertilization and DON increased only under fertilization(P<0.01).Microbial diversity and heating stress significantly affected bacteria and fungi diversity(P<0.01).With microbial diversity declined,bacterial diversity declined.Heating stress significantly reduced bacterial diversity,especially when microbial diversity falls in higher diversity scope.Fungal diversity fluctuated more than bacteria and was significantly reduced by heating stress,especially when microbial diversity fell at low diverisity gradient.Under heating stress,soil accumulated CO2 dropped significantly with the decrease of microbial diversity.PCA analysis showed that alternations of soil enzyme activity after heating stress were mainly associated with microbial diversity,indicating high microbial diversity played an important role in maintaining function stability.In summary,the serial dilution approach decreased soil microbial diversity and significantly modified soil resource and ecosystem function.The relationships between soil microbial diversity and ecosystem function such as the typical funcions plant productivity and litter decomposition validated that soil biodiversity play critical roles in maintaining ecosystem function.