Effects Of Nitrogen And Phosphorus Addition On Grassland Dominant Species And Community Biomass Accumulation In Loess Hilly-Gully Region

Fertilization is considered as an effective management measure to improve grassland productivity and promote grassland restoration.This paper studies the dynamics of grassland community biomass accumulation and the change of species contribution,and discusses the mechanism of nitrogen and phosphorus addition driving the change of community structure and affecting community diversity and stability,which can provide theoretical basis for improving grassland ecosystem function and promoting vegetation restoration by applying fertilization measures in loess hilly region.In this paper,the grassland community in loess hilly region was taken as the research object,and different nitrogen and phosphorus(N:0,50,100 kg N hm^-2 a^-1;P:0,40,80 kg P₂O₅ hm^-2 a^-1)The leaf functional traits,stem and leaf biomass,aboveground biomass and species diversity of five plants in different months were added.The main results are as follows:1.From May to August,the response of leaf water content of five dominant plants to nitrogen and phosphorus addition treatment was not consistent.Nitrogen addition increased leaf length,leaf width,SLA and decreased LDMC of five dominant plants,among which Lespedeza davurica was less sensitive to nitrogen than the other four dominant plants.The dominant plants with nitrogen and phosphorus added together have longer and wider leaves and higher SLA than those with nitrogen or phosphorus addition alone.In May,Bothriochloa ischaemum and Stipa bungeana tended to increase the leaf length,while L.davurica tended to increase the LDMC,Artemisia gmelinii and Potentilla tanacetifolia tended to increase the SLA and leaf width.In June,B.ischaemum and S.bungeana tended to increase the LDMC.In July,although B.ischaemum and S.bungeana increased the leaf length at the same time,B.ischaemum,a grass C₄ plant,tended to increase the SLA,while L.davurica,A.gmelinii and P.tanacetifolia tended to increase its LDMC.In August,B.ischaemum tends to increase the width and water content of leaves.2.From May to August,among the five dominant species of plants,gramineae B.ischaemum and S.bungeana distributed more biomass to the leaves,while L.davurica,A.gmelinii and P.tanacetifolia distributed more evenly to the stems and leaves.Nitrogen addition increased the stem and leaf biomass of five dominant plants,while phosphorus addition promoted the stem and leaf growth of L.davurica and A.gmelinii,and only increased the leaf biomass of two gramineae plants.The single addition of nitrogen,phosphorus and nitrogen and phosphorus delayed the initial flowering period of B.ischaemum,and the initial flowering period of S.bungeana was only delayed under N100 treatment,but it had no significant effect on the initial flowering period of L.davurica,A.gmelinii and P.tanacetifolia.3.Compared with phosphorus addition alone,the increase of community biomass is greater with nitrogen addition,and the community biomass with nitrogen and phosphorus addition is higher than that with nitrogen or phosphorus addition alone.Under the treatment of N₅₀ combined with phosphorus addition,the biomass of five dominant species in grassland community was relatively balanced.From June to July,the plant height of various dominant plants increased rapidly,and the absolute and relative growth rates of grassland community biomass were the highest from July to August.Compared with the non-fertilization treatment,the species diversity,Shannon-Wiener diversity index,Simpson dominance index and Pielou evenness index of N₅₀ combined with phosphorus addition have no significant changes compared with the non-fertilization treatment,while the N₁₀₀ combined with phosphorus addition is significantly lower than that of the non-fertilization treatment.Overall,it was shown that fertilization could increase the aboveground biomass of grassland communities in the semi-arid loess hilly area,and 50 kg N·hm^-2·a^-1 combined with40 kg P₂O₅·hm^-2·a^-1 and 50 kg N·hm^-2·a^-1 combined with 80 kg P₂O₅·hm^-2·a^-1 were suitable proportions to improve grassland productivity and maintain community species diversity and stability.Species attributes and fertilization types jointly determined the distribution of plant biomass of dominant species in grassland communities,and plant height was the dominant factor in the distribution mode of plant biomass distribution and community biomass accumulation dynamics of different dominant species after fertilization.