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Titre : Effects of Precipitation Change and Nitrogen Deposition on Litter Decomposition in Ningxia Desert Steppe

Auteur : 万红云

Grade : Master 2022

Université : Ningxia University

Résumé partiel
As the intermediate link between plants and soil,litter plays an important role in the material cycle and energy flow of the ecosystem,and its decomposition is mainly related to the chemical components of litter,the community of decomposers and abiotic environmental factors.The increase of atmospheric nitrogen deposition and the change of precipitation pattern affect the chemical composition and environment of litter.As a grassland type transitioning from grassland to desert,desert steppe has a fragile ecosystem and an obvious response to climate change.To study the response of litter decomposition to precipitation change and nitrogen deposition in this region is of great significance for understanding the response process of litter decomposition in desert steppe ecosystem to global climate change.In view of this,the litter of Artemisia scoparia,Sophora alopecuroides,Agropyron mongolicum and Stipa breviflora of typical plant communities in desert steppe of Ningxia was selected as the research object.A split-zone design was adopted,and the main area was precipitation treatment:decreased rainfall by 30%（R）,natural rainfall（CK）,increased rainfall by 30%（W） ;the sub-area is nitrogen treatment:addition（10 g·m-2·a-1）and no addition（0 g·m-2·a-1）（excluding atmospheric nitrogen deposition）,a 1-year field experiment was conducted to compare the decomposition characteristics of litter under precipitation change and nitrogen deposition by the field decomposition bag method,analyzed the decomposition rate and chemical composition change characteristics of litter under each treatment,and combined the changes in soil properties,in order to reveal the mechanism of litter decomposition under precipitation change and nitrogen deposition.The results showed that :（1）Different types of litter have different decomposition rates.With the progress of decomposition,the dry matter residual rate decreased gradually,and the overall performance was Gramineae（A.mongolicum,S.breviflora）＞Leguminosae（S.alopecuroides）＞Compositae（A.scoparia）,and the dry matter residual rate of A.mongolicum was 52.67%-64.95%,the dry matter residue rate of S.breviflora was 51.53%-64.25%,the dry matter residue rate of S.alopecuroides was 55.9%-62.68%,and the dry matter residue rate of A.scoparia was 44.68%-62.63%.The Olson exponential decay model showed that A.mongolicum decomposed the slowest（with the smallest k value）,and A.scoparia decomposed the fastest（with the largest k value）,The change of precipitation significantly affected the dry matter residual rate of litter,but the effect of nitrogen deposition was not significant:under the same nitrogen treatment,the increase of rainfall promoted the decomposition,and the decrease of rainfall inhibited the decomposition ;under the same water treatment,nitrogen addition promoted decomposition.（2）The change patterns of chemical components during litter decomposition were different.With the progress of decomposition,the residual rate of lignocellulose（lignin,cellulose and hemicellulose）of the four types of litter showed an overall downward trend.The residual rates of nitrogen and phosphorus all showed a leaching-accumulation-release pattern.The residual rates of carbon and potassium showed a direct release mode,and the residual rate of trace elements（calcium,magnesium and manganese）showed an enrichment-release mode as the decomposition progressed.The stoichiometric ratio of litter increased first and then decreased during the decomposition process,and the ratio was the largest at 212 d.（3）The chemical components of litter were sensitive to the change in water and nitrogen.

Mots clés : precipitation change ;nitrogen deposition ;desert steppe ;litter decomposition ;

Présentation (CNKI)