Exploring the distribution patterns of soil nutrients in aggregates of forests along different altitudes in arid and semi-arid areas can provide a theoretical basis for understanding nutrient cycling in vulnerable mountain ecosystems. In this study, we analyzed the distribution and stability of aggregates in the 0-20 cm soil layer along different altitudes (1380-2438 m) of Helan Mountains and measured the storage and stoichiometric characteristics of organic carbon, total nitrogen, and total phosphorus in soil aggregates. Results showed that the main soil aggregates of Helan Mountains changed from micro-aggregates (0.25-0.053 mm) to macro-aggregates (>0.25 mm) with increa-sing elevation. The mean weight diameter (MWD) and geometric mean diameter (GMD) of soil aggregates in high altitude (2139-2248 m) were significantly higher than those in low altitude (1380-1650 m). The content and storage of organic carbon and total nitrogen in soil aggregates of different size fractions were positively correlated with altitude, while the content of total phosphorus fluctuated with the increase in elevation and distributed uniformly in aggregates. Macro-aggregates and micro-aggregates had more contribution to soil nutrient storage than the silt and clay fractions, indicating that the proportion of aggregates with different size fractions was the key factor affecting soil nutrient storage and that macro-aggregates and micro-aggregates were the main carriers of soil nutrients. Moreover, the C:N ratio in aggregates of different size fractions did not change across different altitudes, whereas the C:P and N:P ratio were higher at mid and high elevations than those at low elevations. Our results indicated that the mid and high elevations of Helan Mountains had higher nutrient storage in the surface soil layer, and that higher content of macro-aggregates and micro-aggregates would help to retain organic carbon and nutrients in the soil. Soil nitrogen limitation was strong at low altitude in our study, suggesting that the appropriate amount of nitrogen addition in low altitudes could improve total nitrogen status during forest cultivation.
探究干旱半干旱区山地森林生态系统不同海拔土壤养分在团聚体中的分布规律,可为理解脆弱山地生态系统养分循环提供理论依据。本研究以贺兰山不同海拔(1380～2438 m)土壤为对象,分析0～20 cm土层团聚体分布及其稳定性、不同粒级团聚体有机碳、全氮、全磷储量及其化学计量特征。结果表明: 随海拔升高贺兰山主要土壤团聚体由微团聚体(0.25～0.053 mm)转变为大团聚体(>0.25 mm),平均重量直径(MWD)和几何平均直径(GMD)在高海拔样地(2139～2248 m)显著高于低海拔样地(1380～1650 m)。各粒级团聚体有机碳、全氮含量和储量随海拔升高呈增大趋势;全磷含量随海拔升高呈波动趋势,且在各粒级团聚体分布均匀。大团聚体和微团聚体对土壤养分具有更高的贡献率,各粒级团聚体比例是影响土壤养分的关键因素,大团聚体和微团聚体是土壤养分的主要载体。各粒级团聚体C∶N在不同海拔变化不显著,C∶P和N∶P在中高海拔显著高于低海拔。贺兰山中高海拔的表层土壤具有更高的养分储量,较高含量的大团聚体和微团聚体有助于有机碳和养分的固持,低海拔土壤氮素限制高,在森林培育过程中可通过适当添加氮肥以改善低海拔土壤全氮状况。.
Keywords: aggregates; elevation; organic carbon; stoichiometry; total nitrogen; total phosphorus.