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Northwest A&F University (2021)

Response of Typical Grassland Community and Its Dominant Species to Nitrogen and Phosphorus Addition at Semiarid Loess Hilly-gully Region

陈志飞

Titre : Response of Typical Grassland Community and Its Dominant Species to Nitrogen and Phosphorus Addition at Semiarid Loess Hilly-gully Region

Auteur : 陈志飞

Grade : Doctoral Dissertation 2021

Université : Northwest A&F University

Résumé partiel
The problems of sluggish restoration succession,simplistic community structure and poor ecological function coexist in the farming-withdrawn grassland on semiarid loess hilly-gully region.Grassland production and ecosystem services are widely co-limited by soil N and P availability in this region because of high nutrient loss through soil erosion and intensive cultivation.Rational N and P combination can not only efficiently improve grassland productivity,but also optimize community structure and promote grassland restoration.Three grassland communities dominated by annual forbs(AF),perennial grass(PG)and perennial forb(PF)were selected.A split-plot N and P addition experiment(main-plot:0,25,50,and100 kg N ha-1 yr-1 ;subplot:0,20,40 and 80 kg P2O5 ha-1 yr-1)was conducted on three grassland communities during 2017-2019.We systematically examined the effects of N and P addition on leaf functional traits and photosynthetic physiology,stoichiometry characteristic,nutrient use and resorption efficiency of different dominant species and functional group composition and its relationship with community productivity,species diversity and community stability.The main results are as follows :(1)N addition alone significantly increased area-based leaf N content and N:P ratio of Stipa bungeana only,while light-saturated net photosynthetic rate(PNmax)was increased significantly in S.bungeana,Bothriochloa ischcemum and Lespedeza davurica.Area-based leaf N content,PNmax and photosynthetic nitrogen use efficiency(PNUE)increased significantly only in L.davurica.N and P combined addition caused significantly lower area-based leaf N content but higher stomatal conductance,PNUE and PNmax in B.ischcemum and S.bungeana compared to N addition alone.The stomatal conductance,area-based leaf N and P content,PNmax and PNUE of L.davurica were increased significantly under N and P combined addition.The LNCa/LPCa for optimum PNmax and PNUE was changed with species.The PNmax and PNUE of B.ischaemum and S.bungeana had a peak when LNCa/LPCa attained~11 and~20.L.davurica tended to retain greater PNmax and PNUE at lower LNCa/LPCa.B.ischaemum achieved higher photosynthetic capacity through the improvement of nutrient use efficiency rather than leaf nutrient content,while the increased PNmax in S.bungeana might be due to improved stomatal conductance and increased leaf N content and nutrient use efficiency.L.davurica tended to retain greater photosynthetic capacity and nutrient use efficiency at higher leaf P content and stomatal conductance.(2)B.ischaemum and S.bungeana possess relatively higher N and P resorption and use efficiency,but relatively lower leaf N and P under unfertilized treatment.Leaf N content,N:P,P resorption efficiency and aboveground biomass(AGB)of B.ischaemum and S.bungeana increased significantly under N addition alone.P addition alone significantly increased leaf P,but had no effect on AGB.Under 50 and 100 kg N ha-1 yr-1 combined with P,N:P of B.ischaemum and S.bungeana decreased significantly compared to N addition alone,but AGB exhibited further increases.L.daurica possessed had relatively higher leaf N and N:P,but relatively lower leaf P,N and P resorption and use efficiency under unfertilized treatment.Leaf N and P,N and P resorption efficiency and aboveground biomass of L.daurica increased significantly after P alone and 25 kg N ha-1 yr-1 combined with P addition.Artemisia sacrorum and Artemisia scoparia had relatively higher leaf P and P resorption efficiency,but lower N:P and N and P use efficiency.N or P addition alone had no significant effect on leaf N,N and P resorption efficiency and AGB of A.sacrorum and A.scoparia.

Mots clés : grassland restoration ;N and P fertilization ;photosynthetic physiology ;nutrient use ;community structure ;diversity;stability ;

Présentation (CNKI)

Page publiée le 12 novembre 2021