黄土高原天然草地3种优势物种细根分解及养分释放对模拟氮沉降的响应

Effects of Stimulated Nitrogen Deposition on the Fine Root Decomposition and Nutrient Release of Three Dominant Species in Natural Grassland on the Loess Plateau

细根分解是草地土壤有机质和养分的主要来源,全球N沉降背景下细根分解动态变化对生态系统碳和养分循环具有重要意义。采用埋袋法研究黄土高原天然草地3个优势物种细根分解速率和养分释放规律及其对模拟N沉降(10g·N/(m2·a))的响应。结果表明:细根分解过程分为快速(0~60d)和慢速分解(60~719d)2个阶段。大针茅、甘青针茅和白莲蒿细根分解60d的质量残留率分别为86.3%,86.2%,90.7%,分解719d的质量残留率分别为58.1%,64.7%,70.5%,表明细根分解速率大小为大针茅>甘青针茅>白莲蒿。相关分析表明,细根分解常数与细根初始N含量、N/P值呈显著的正相关关系,与初始C含量、C/N值呈显著的负相关关系。随着根系分解,3种细根C元素表现为直接释放,N元素表现为N富集,P元素表现为富集-释放模式,整体呈波动式下降。模拟N沉降显著抑制了3种植物细根的分解,使大针茅、甘青针茅和白莲蒿细根分解系数分别显著降低了21.3%,26.8%,47.4%。模拟N沉降使大针茅、甘青针茅和白莲蒿分解末期C元素分别增加了26.8%,20.7%,16.6%,N元素分别增加了18.2%,17.0%,13.4%,而对P残留率均没有显著影响。综上,未来氮沉降的增加会抑制黄土高原封育草地优势物种的细根分解速率,减慢其细根分解向土壤输入C和N养分的过程。

Fine root decomposition is the main source of soil organic matter and soil nutrients in grasslands.Fine root decomposition dynamics under the background of global nitrogen deposition plays an important role in carbon and nutrient cycling of terrestrial ecosystem.In this study,buried bag experiment was used to investigate fine root decomposition rate and nutrient release characteristics of three dominant grass species on the Loess Plateau,and their response to nitrogen deposition（10 g N/（m2·a））.The results showed that the decomposition process of fine roots could be divided into rapid（0~60 d）and slow（60~719 d）decomposition stages.The root mass residual rates of Stipagrandis,Stipaprzewalskyi and Artemisia sacrorum were86.3%,86.2% and 90.7% on the 60 th day,respectively,and they were 58.1%,64.7% and 70.5% on the719 th day,respectively,indicating that the fine roots decomposition of S.grandis was the fastest and it ofA.sacrorum was the lowest.Correlation analyses showed that the decomposition constant of fine roots was positively related with nitrogen content and N/P ratio,and negatively correlated with the carbon content and C/N ratio.During the fine root decomposition,the carbon transfer models of the three species were all direct releasing,and the nitrogen transfer models were enriching,and phosphorus exhibited enriching-releasing model,and all of them tended to decrease generally.Simulated nitrogen deposition suppressed the fine root decomposition rates of S.grandis,S.przewalskyi and A.sacrorum,with the decomposition constants decreased by 21.3%,26.8% and 47.4%,respectively.While,it increased the carbon remaining rates of S.grandis,S.przewalskyi and A.sacrorum by 26.8%,20.7% and 16.6%,respectively,and increased nitrogen remaining rates by 18.2%,17.0%and 13.4%at the end of our study period.However,phosphorus remaining rates of fine roots in all three species were not significantly influenced by simulated nitrogen deposition.Nitrogen deposition in the future will inhibit the fine roots decomposition rates of the three dominant species in fenced grassland on the Loess Plateau,and slow down the process of inputting carbon and nitrogen from plant into soil.