土壤元素失衡是导致高寒草甸退化的重要诱因

Imbalance of soil elements drives the degradation of alpine grasslands

土壤元素失衡是造成高寒草甸退化的关键诱因,明晰其过程与机制是高寒草甸生态系统可持续利用和退化草地恢复的重要内容。以我国典型青藏高原高寒草甸生态系统为研究对象,选取围封1年样地作为短期恢复、围封6年样地作为中期恢复及围封15年样地作为长期恢复阶段,分析了这些样地的土壤基本理化性质。研究发现,退化高寒草甸的恢复未改变土壤pH,但增大了土壤保水能力和电导率。土壤有机碳和全氮含量随恢复进程变化敏感,而磷含量的变化并不明显,随着恢复时间的增加土壤C∶N,C∶P和N∶P显著升高,土壤可利用氮素特别是铵态氮的供应能力得到显著提升,长期恢复阶段的土壤铵态氮含量为短期恢复阶段的3.1倍。退化草地的恢复大幅度增加了高寒草甸生态系统地上生物量,这进一步增加了植物对土壤中的碳和氮输入,使土壤中的碳氮周转变快,诱发了植物-土壤之间的正反馈,形成良性循环,使退化草甸得以改善。本研究从退化高寒草甸恢复角度初步证实,土壤碳氮与磷元素比例失衡是造成高寒草地退化的重要诱因,研究结果对高寒草地的养护管理以及退化高寒草地的恢复工作具有重要意义。

Imbalance of soil elements is one of the major factors driving alpine grassland degradation.Clarifying the processes and mechanisms for the imbalance of soil elements is important for the restoration and sustainable use of degraded alpine grasslands.To achieve this,we analyzed basic soil physicochemical properties across a chronosequence:a 1-year enclosed site as shortterm restoration stage,a 6-year enclosed site as medium restoration stage,and a 15-year enclosed plot as long-term restoration stage in typical alpine grasslands in the Qinghai-Tibet Plateau.Restoration of degraded grassland did not change soil pH,but increased soil water-holding capacity and electricity.Soil organic C and total N contents changed greatly across the restoration stage,while soil P content remains unchanged.With increasing restoration duration,C∶N,C∶P and N∶P ratios and available N(especially ammonium)in soil remarkably increased.The ammonium content at long-term restoration stage was 3.1 times higher than that after one-year restoration.The restoration of degraded grasslands greatly increased aboveground biomass,resulting in the increased soil C and N inputs through plant litter and rhizodeposition.Increased C and N inputs by plants triggered rapid C and N turnover in soil.Such a strong positive feedback help restore the degraded alpine grasslands.These findings indicate that imbalance of soil elements should be responsible for the degradation of alpine grasslands,providing an important basis for the restoration of degraded alpine grasslands and sustainable use of alpine grasslands.