Responses Of Stoichiometry Characteristics Of N,P And Stoichiometric Homoeostasis In Forest-steppe Ecotone Plants To Nitrogen Addition

Ecological stoichiometry is a tool for studying various elements needed by organisms and affecting population dynamics and ecosystem productivity.It is mainly used for the analysis of restrictive elements in plant growth.The N and P ecological stoichiometry characteristics of plants are the result of long-term adaptation of plants to environmental conditions.Therefore,the study of N and P stoichiometry can not only grasp the environmental adaptation strategies of plant populations,but also help to understand the nutrient limitation,population evolution and development trend of plants.Atmospheric nitrogen deposition is one of the important ways of nitrogen input in terrestrial ecosystem,which affects the balance of soil nutrient supply,plant nutrient uptake and population dynamics.In order to grasp the N and P stoichiometry,the change of stoichiometric homoeostasis and the evolution mechanism of N and P limitation of plants in forest-steppe ecotone under the background of increasing atmospheric nitrogen deposition,choose Cleistogenes squarrosa,Lespedeza daurica,and Potentilla tanacetifolia as the target,through the field artificial nitrogen addition(10,20,40 kg N·hm2·a-1),the N and P stoichiometry characteristics and stoichiometric homoeostasis of leaves and roots,and three plants organisms,the change of quantity,from the perspective of stoichiometry,its response mechanism to atmospheric nitrogen deposition.The main results are as follows:1.The changes of N and P in the leaves and roots of the three plants were different,the N and P contents of the leaves of the three plants increased with the increase of nitrogen concentration.The P in the leaves increased in 2018 compared with 2017.Nitrogen addition in 2018 significantly increased the content of N and P in leaves(P<0.01).The increase of N and P contents in leaves of C.squarrosa was smaller than that of the other two plants(P<0.01).The content of P in the roots in 2018 was also higher than that in 2017.The content of N and P changed with the increase of nitrogen concentration in 2018.Overall,the P content in the leaves increased in the second year of nitrogen application.2.In the two years of nitrogen addition treatment,the N:P of leaves of three plants' region ranged from 4.7 to 11.2.C.squarrosa was the smallest in two years.In the second year of nitrogen addition,the N:P of C.squarrosa showed a significant trend,and increased with the increasing of nitrogen concentration,L.daurica on the contrary.In the two years of nitrogen addition,the N:P of roots of three plants ranged from 3.4 to 42.6,and there was no obvious change trend in 2017.The N:P of roots of P.tanacetifolia was the largest;but in 2018,the N:P of roots of C.squarrosa and L.daurica decreased with the increase of nitrogen application concentration,while the N:P of roots of L.daurica was the largest,while the N:P value of roots of P.tanacetifolia.3.Under the background of nitrogen addition,the above-ground biomass of the three plants showed an increasing trend,but the biomass of C.squarrosa and P.tanacetifolia showed a peak,and the L.daurica did not appear yet.The soil N and P contents also increased with the increase of nitrogen addition concentration.4.The contents of N and P in leaves of C.squarrosa did not increase significantly with the addition of N,the index of N and P in leaves was 1.706 and 9.960,respectively,which were higher than those of the other two plants.With the increase of nitrogen addition,biomass began to decrease when N:P exceeded 5.4,and the population might change from N limitation to P limitation.