若尔盖高寒草地退化沙化过程中土壤养分与团聚体结构的变化特征

Change of soil nutrient and aggregate structure during the desertification process of grassland in Zoige

若尔盖地处青藏高原东缘,是黄河上游重要的水源涵养地。近来受过度放牧、鼠虫害等影响,若尔盖高寒草地出现严重退化,部分草地已完全沙化。草地沙化已成为若尔盖高寒草地生态安全所面临的重大问题。研究以若尔盖典型的沙化地区麦溪乡为研究对象,以植被覆盖率为沙化梯度划分标准,分别划分未退化、轻度退化、中度退化、重度退化和极度退化5种不同退化阶段草地,探究退化沙化过程中草地土壤养分与团聚体结构变化特征。结果表明:(1)退化沙化过程中,土壤养分含量总体随着草地沙化程度的加剧而显著下降(P<0.05)。(2)退化沙化过程中土壤团聚体结构发生明显变化,团聚体平均重量直径(MWD)、几何平均直径(GWD)随着沙化程度的加剧而显著降低(P<0.05);各粒级团聚体百分比仅5-2 mm粒级团聚体在重度退化阶段发生显著降低变化(P<0.05),其他粒级并未表现出明显的变化趋势。(3)团聚体MWD与微生物生物量、有机质、全氮、硝态氮、有机碳均呈显著或极显著正相关,与pH呈极显著负相关(P<0.01)。在整个草地退化沙化过程中,土壤养分含量显著下降,土壤结构受到严重破坏,二者之间变化关系紧密。草地沙化治理与防护过程中,要兼顾土壤结构修复与养分输入,处理好土壤团聚体结构稳定与养分转化间的交互关系。

Zoige is an important water source for the upper reaches of the Yellow River which locates on the eastern edge of the Qinghai-Tibet Plateau. In recent years, due to overgrazing, rodents and pests and other reasons, the Zoige alpine grassland has been seriously degraded, and some grasslands have completely desertified. Grassland desertification has become a major problem imperiling the ecological security of the Zoige alpine grassland. This study was conducted at the Maixi Township, the main desertification area of Zoige. According to the vegetation coverage rate of the desertified grassland, we divided the grassland to five different desertification stages: non-desertification, mildly desertification, moderately desertification, severely desertification and extremely desertification. Soil nutrient and aggregate structure were measured in these desertified grassland. The results showed that:(1) In the process of desertification, the soil nutrient content decreased significantly(P<0.05).(2) The structure of soil aggregates changed significantly during desertification. The average weight diameter(MWD) and geometric mean diameter(GWD) of aggregates decreased significantly as the degree of desertification deepened(P<0.05). In terms of the percentages of the aggregate fractions of different particle sizes, only the percentage of 5-2 mm particle size aggregate decreased significantly at the stage of severe desertification.(3) The aggregates MWD had significantly positive relationship with microbial biomass, organic matter, total nitrogen, nitrate nitrogen and organic carbon respectively, but had significantly negative relationship with pH(P<0.01). During the desertification process of grassland, the soil nutrient content decreased significantly and the soil aggregate structure was seriously damaged. Therefore, in the process of controlling and recovering desertified grassland, it is necessary to take into account the soil structure restoration and nutrient input and improve the interaction between soil aggregate structural stability and nutrient conversion.