高寒草甸退化指示种黄帚橐吾凋落物对土壤氮磷转化的影响

Due to over-grazing and other disturbance over recent decades, large areas of typical alpine meadow was regressive succession to poisonous weeds degraded meadow, which was dominated by Ligularia virgaurea. Grassland degradation could have severe threaten to functioning and stability of ecosystem in Qinghai-Tibet Plateau. As an indicator species of degraded alpine meadow, previous research found that L. virgaurea litter could restrict decomposition and nutrient release of litter mixture, while their growth could decrease the content of soil available nitrogen and soil available phosphorus. However, so far it remains largely unclear about how decomposition of L. virgaurea litter and interaction with plant growth affect the transformation of soil nitrogen and phosphorus in alpine meadow. Therefore, taking the L. virgaurea as the research object, we conduct a field experiments with treatments of addition of litter and remove of plant growth, to analyses the direct and indirect effect of L. virgaurea on soil total nitrogen, soil total phosphorus, soil available nitrogen, soil available phosphorus, soil physicochemical property and soil extracellular enzyme activity. The effects of L. virgaurea litter decomposition, and coordinated / antagonism interactions with plant growth on the soil transformation of soil nitrogen and phosphorus will be explored. This project will provide with supplement information to poorly aware of the relationship between litter decomposition and transformation of soil nutrient, and improve our understandings about the nutrient cycle action of ecosystem in process of degraded alpine meadow in which dominant species shifts were occurred, and thus having important theoretical and practical significance.

近年来，受过度放牧等干扰因素的影响，青藏高原高寒草甸大面积逆向演替成以黄帚橐吾为优势的毒杂草型退化草甸，严重威胁生态系统的功能和稳定。黄帚橐吾，作为高寒草甸退化指示种，前期研究表明其凋落物能延缓混合凋落物分解及氮磷释放，且其生长能降低土壤可用性氮磷含量。然而，截至目前，黄帚橐吾凋落物分解如何影响土壤氮磷转化过程尚不清楚。本项目拟以黄帚橐吾为研究对象，通过不同凋落物添加和植被去除处理的野外试验方法，分析不同处理条件对凋落物分解的重量损失及氮磷释放速率，土壤氮磷、可利用氮磷、理化性质以及胞外酶活性变化的直接和间接作用，以此探讨黄帚橐吾凋落物分解以及与生长的协同/拮抗相互作用对土壤氮磷转化的影响。本研究不仅是对凋落物-土壤养分转化相互关系认知不足的补充，也可加深理解高寒草甸退化过程中优势种变化对生态系统养分循环功能的作用，具有重要的理论价值和现实意义。

凋落物作为生态系统养分循环的重要组成部分，在土壤养分动态中具有关键作用。然而针对凋落物分解与植物生长对土壤氮磷转化的相对贡献尚不清晰。近年来黄帚橐吾由于过度放牧等干扰在高寒草甸大面积扩张，严重威胁生态系统的可持续发展。基于此，项目以三江源区黄帚橐吾为优势的高寒草甸为研究对象，设置凋落物和植物生长的去除处理的野外试验，探究了凋落物沉积与地上生长对土壤氮磷转化的贡献，分析了其直接和间接作用的相对大小和生长季差异；并结合凋落物分解及氮释放特征研究了凋落物量变化对土壤氮转化的影响。目前研究结果发现：1）黄帚橐吾凋落物和地上生长共同抑制了土壤氮转化，且凋落物贡献更大；同时地上生长不利于土壤磷转化；二者共同作用可能是拮抗的，而不是协同效应。2）凋落物和地上生长的作用均依赖于其他物种，黄帚橐吾主要通过与其他物种的拮抗作用而间接影响土壤氮磷转化。当其他物种被去除黄帚橐吾单独存在时，只有其凋落物能直接限制氮转化且贡献降低，而地上生长没有影响。3）凋落物和地上生长对土壤速效养分的影响不随生长季变化而波动，而凋落物沉积不利于非生长季微生物生物量氮积累。4）黄帚橐吾凋落物量的增多能持续延缓对分解及氮释放的抑制，尤其对氮释放负效应更大；且对土壤速效氮、微生物氮积累以及氮转化的抑制效应也持续加剧。本研究以高寒草甸黄帚橐吾为例揭示了凋落物分解和地上生长对土壤养分转化的贡献及机理，有助于拓展对生态系统养分循环过程的理解，为研究高寒草地毒杂草扩张以及退化草地恢复治理提供理论基础。