10年禁牧未改变藏西北高寒荒漠植物水氮利用效率

Ten-year livestock exclusion did not affect water and nitrogen use efficiency of alpine desert-steppe plants in Northwest Tibet

在气候变化和过度放牧影响下,高寒草地退化日趋严重。当前,围栏封育作为退化草地生态恢复的主要措施之一,其对植物功能性状和生理过程影响的研究相对较少。以藏西北荒漠草原植物为对象,选取植物叶片碳(LCC)和氮含量(LNC)及稳定同位素组成(δ^(13)C和δ^(15)N)来表征植物水分利用效率(WUE)和氮素利用效率(NUE),以期探明围栏封育对高寒荒漠草原植物WUE和NUE的相对影响。结果表明:1)高寒荒漠草原不同功能群植物间LCC、LNC、δ^(13)C和δ^(15)N存在差异;2)在植物群落和功能群水平上,围栏封育对LCC、LNC、δ^(13)C和δ^(15)N均无显著影响;3)土壤含水量和pH值是影响荒漠植物叶片δ^(13)C的主要因子,表明植物内在WUE主要受土壤因素的调控。生长季气温是影响叶片δ^(15)N的主导因子,表明气候条件是影响藏西北荒漠草原生态系统氮循环的主导因素;4)荒漠草原植物WUE和NUE之间无明显权衡关系。综上所述,短期围栏封育并不会显著改变藏西北荒漠草原植物WUE和NUE;且荒漠草原生态系统碳氮循环主要受当地环境因素影响。因此,建议在脆弱高寒荒漠生态学研究中加强关于植物生理和功能性状对环境变化响应过程的研究,从而更好地理解群落构建和演替以及养分循环机制。

Under climate change and overgrazing,the area of degraded grassland is increasing in the Tibetan Autonomous Region of China.A common measure for recovering these degraded grasslands is grazing exclusion using fencing.However,the effects of fencing on plant functional traits and physiological processes are still unclear.In this study,we chose leaf carbon content(LCC)and leaf nitrogen content(LNC)and stable carbon and nitrogen isotopic compositions(δ^(13)C and δ^(15)N)to characterize the water use efficiency(WUE)and nitrogen use efficiency(NUE)of alpine desert-steppe plants in Northwest Tibet to clarify the effects of livestock exclusion by fencing on species WUE and NUE.We found that LCC,LNC,δ^(13)C and δ^(15)N of alpine desert-steppe plants differed between different plant functional groups.At both community and plant functional group levels,livestock exclusion had no significant effects on LCC,LNC,δ^(13)C and δ^(15)N.Rather,soil water content and pH value were the main factors affecting the community weighted mean of leaf δ^(13)C,indicating that soil properties can significantly affect the internal WUE of plants.Growing season temperature was the dominant factor affecting the community weighted mean of leaf δ^(15)N,indicating that climatic conditions are the main factor affecting ecosystem nitrogen cycle of alpine desert-steppes in Northwest Tibet.There were no trade-offs between WUE and NUE for alpine desert steppe plants.In conclusion,our study confirms that the short-term livestock exclusion in Northwest Tibet does not significantly alter the WUE and NUE of desert-steppe plants and that local environmental factors have significant effects on carbon and nitrogen cycling of the alpine desert-steppes.Therefore,it is necessary to study plant physiological and functional traits in response to environmental change for a better understanding of plant community assembly and evolution and to understand nutrient cycling in alpine grassland ecosystems.