Abstract:

In order to explore the effects of enclosure on stability of soil aggregates, the dessert steppes of unenclosed, 3-year enclosed, 5-year enclosed, 7-year enclosed and 10-year enclosed in Ningxia were selected as investigative plots adopting spatial sequences instead of time series. The percentage of different particle sizes, destruction rate of soil aggregates, and mean weight diameter (MWD) at 0~40 cm soil depth were analyzed using dry and wet sieving methods. The results showed that: the enclosure favored the formation of soil aggregates. The contents of <0.25 mm dry sieve aggregates, especially those at 0~10 cm and 10~20 cm soil depth, declined with extension of enclosure time, and the 10-year enclosed grassland was the lowest. The contents of <0.25 mm water-stable aggregates at 0~10 cm and 20~40 cm soil depths changed significantly, and the minimum values appeared at 7-year and 10-year enclosed grasslands, respectively. The mean weight diameter presented as a decreased-increase trend with grassland restoration and the highest was the 10-year enclosed grassland. The destruction rates of soil aggregates were lower in 7-year and 10-year enclosed grasslands and higher in unenclosed and 3-year enclosed grasslands. For vertical distribution, the contents of >5 mm macro-aggregates increased with increasing depth.

Key words: Enclosure, Dessert steppe, Soil aggregate, Mean weight diameter, Destruction rate of soil aggregates

摘要：

以空间序列代替时间序列，采用干筛法和湿筛法研究了围封禁牧条件下宁夏荒漠草原恢复演替过程中0~40 cm土层土壤团聚体组成、破坏率及平均重量直径（MWD）等指标，以探讨围封对荒漠草原土壤团聚体稳定性的影响。结果表明：围封有利于荒漠草原土壤团聚体的形成，随围封年限的增加，<0.25 mm土壤微团聚体含量总体呈下降趋势。其中，<0.25 mm干筛团聚体含量在0~10 cm和10~20 cm土层变化显著，均以围封10年的草地最低；<0.25 mm水稳性团聚体含量在0~10 cm和20~40 cm 土层变化显著，其中0~10 cm土层以围封7年的草地最低，20~40 cm土层以围封10年的草地最低；随围封年限的增加，土壤团聚体平均重量直径呈先降低后增加的趋势，以围封10年的草地最高，团聚破坏率则以围封7年、10年的草地较低，未封育和封育3年的草地较高。从垂直分布看，随剖面深度的增加，大团聚体特别是>5 mm粒级团聚体含量显著增加。

关键词: 围封, 荒漠草原, 土壤团聚体, 平均重量直径, 团聚体破坏率