Ecological Stoichiometry Characteristics Of Plant-litter-soil Under Different Vegetation Types In The Semi-arid Loess Small Watershed

Ecological stoichiometry is an effective method to study the balance of elements and energy flow in the ecosystem.Defining the stoichiometry characteristics of plants and litter under different vegetation types,to clarify the changing laws of soil nutrient and stoichiometry ratios with soil depth,and to understand the interrelationship between plants,litter and soil nutrients is of great significance for revealing the nutrient conversion and balance mechanism of ecosystems during vegetation restoration on the Loess Plateau.It can provide a feasible basis for the selection of vegetation restoration types on the Loess Plateau.In this study,five vegetation types(Stipa bungeana grassland,Leymus secalinus grassland,Medicago sativa grassland,Caragana korshinskii shrub,and Armeniaca sibirica forest)in the semi-arid loess small watershed were selected as research objects.Analyzed the carbon(C),nitrogen(N),phosphorus(P)concentration and ecological stoichiometry characteristics of leaves,stems,roots,litter and soil under different vegetation types.The results showed that:(1)The nutrient concentration of each organ in the five typical vegetation was leaf >stem > root.The changes of C,N,P concentrations and stoichiometry ratio were significantly affected by the type of vegetation and the type of organ,respectively,but only the C and N concentrations were significantly affected by the interaction between the type of organ and the type of vegetation.Among different vegetation types,the C concentration in the leaf,stem,root and litter of A.sibirica was significantly highest,and S.bungeana was significantly lowest.The N concentration,N:P and litter C:P,N:P of C.korshinskii were significantly higher than those of other vegetation types.The C:N and C:P of leaf,stem and root respectively showed that L.secalinus had the highest significantly and C.korshinskii had the lowest significantly.Litter N,P,C:N had no significant differences among different vegetation types.Under all vegetation types,the concentrations of C,N,and P in leaves were higher than litter,and C:N,C:P and N:P showed that litter was higher than leaf.The nutrient reabsorption rate and nutrient utilization efficiency of the five typical vegetation of C,N,and P were the highest for P and the lowest for C.Among them,there was no significant difference in the nutrient resorption rate and nutrient use efficiency of C and P for different vegetation types.C.korshinskii and M.sativa had the highest N nutrient resorption rate,but the nutrient use efficiency were the lowest.(2)Vegetation type and soil depth had effects on soil SOC,TN and TP,but only soil TN concentration was affected by their interaction.The differences in soil SOC and TN concentrations under various vegetation types were mainly concentrated in the 0-20 cm soil layer.The concentrations of soil SOC and TN in C.korshinskii shrub were significantly the highest,and the concentrations of soil SOC and TN in L.secalinus grassland were significantly the lowest.The concentration of soil TP in different soil layers had no significant difference among vegetation types.The soil stoichiometry ratios of various vegetation types were different in different soil layers.In the soil layers of 0-20 cm and 20-40 cm,except for the soil C:N,which was the highest in L.secalinus grassland,the soil C:P and N:P were all the highest in C.korshinskii shrub.The soil SOC,TN and TP under the five planting types were significantly positively correlated with each other.Soil C:N and C:P,C:P and N:P were all positively correlated,and C:N and N:P was negatively correlated.(3)On the whole,the correlation of C,N concentrations and C:N,N:P between plants and litters were significantly positive,respectively,while the correlation of P concentration and C:P between plants and litters did not reach a significant level.The correlation of N concentration and N:P between leaf,stem and root and soil were significantly positive,while C:P was significantly negative.The correlation of C and P concentration between plant organs and soil did not reach significant level.The correlation of C,N,P concentration and C:N,C:P,N:P between litter and soil also did not reach significant level.However,among different vegetation types,the correlation of C,N,P concentration and stoichiometry ratio were different among plants,litter and soil,indicating that litter nutrients mainly came from plant tissues,and the regulation of nutrients by plants in the process of growth and development was not only related to the supply of soil nutrients,but also affected by their own growth characteristics.The linear regression analysis showed that the C,N,P concentrations and stoichiometry ratios of C.korshinskii and A.sibirica organs were absolute steady state.The C,N,P concentrations and stoichiometry ratios of each organ of S.bungeana and M.sativa were slightly stronger than that of L.secalinus as a whole.In terms of element level,the internal stability of N element in the study area was the strongest,followed by C element and N:P.Except for C element and N:P of M.sativa and L.secalinus roots,the other indexes were homeostasis.At the organ level,the internal stability of C,N,P and stoichiometry of stem was the strongest,except that P of L.secalinus and C:N of M.sativa were weak steady state,the others were homeostasis,while the C,N,P and stoichiometry of root were the weakest and most of them were sensitive.In summary,vegetation types had a significant impact on the stoichiometry characteristics of plants,litter and soil in small loess watersheds,and there was a certain correlation among the three ecological stoichiometry characteristics.In addition,the changes of plant nutrients and their ratios were also related to the distribution and tradeoff of nutrients among different organs.Different plants can adjust their own nutrient reabsorption efficiency and utilization efficiency to maintain the internal stability of their elements to cope with environmental changes.The nutrient change of litter was mainly regulated by the change of plant leaf nutrient,and the change of soil nutrient and its ratio was also affected by soil depth.In this study area,the comprehensive ecological stoichiometry characteristics of C.korshinskii shrub were stronger,and the nutrient use efficiency and internal stability were relatively higher,which was more conducive to improving local soil quality and promoting nutrient cycling.