沙漠绿洲过渡带柽柳灌丛沙堆-丘间地系统土壤养分空间异质性

Spatial variation of soil nutrients of Tamarix ramosissima nebkhas and interdune areas in a desert-oasis ecotone

以塔克拉玛干沙漠南缘策勒沙漠绿洲过渡带为研究区,选取植被盖度依次为30%、15%—20%、10%和<5%的4个典型样地,对各样地的柽柳灌丛沙堆-丘间地系统典型部位0—10 cm和10—20 cm土壤进行系统采样,分析土壤枯落物、有机质、全效N、P、K和速效N、P、K含量,从风沙地貌的角度研究过渡带沙漠化进程中土壤养分分布特征。结果表明:(1)随着植被总盖度的降低,灌丛沙堆表层0—10 cm土壤的枯落物、有机质、全N、全K、速效K含量呈降低趋势,平均降幅为69.3%、37.0%、35.3%、8.3%和24.5%。全P含量没有明显的变化,速效N和速效P含量呈先减小后增大的趋势;(2)从灌丛下→沙堆边缘→丘间地→风影区,土壤枯落物、有机质、全N、全P、速效N、速效P、速效K含量表现出先减小后增大的趋势,最大值位于灌丛下部位,最小值位于丘间地,但在植被盖度<5%的样地,沙堆-丘间地系统各部位之间养分含量无显著性差异;(3)与0—10 cm土层相比,10—20 cm土层的枯落物、有机质、全N、全P和速效P含量显著降低,平均降幅为40.0%、27.0%、25.0%、4.5%和2.0%,全K、速效N和速效K含量明显增加,平均增幅为4.8%、103.3%和12.1%。随着植被盖度的降低,10—20 cm土层的养分含量具有与0—10 cm土层相对一致的变化趋势;(4)灌丛的生物反馈作用使得灌丛下部位具有明显的养分富集效应,但随着植被总盖度的降低和风沙活动不断加剧,非生物因素逐渐占据主导,灌丛的养分富集效应趋于减弱和消失。

In this study four kinds of typical plots, with vegetation cover of 30%, 15%-20%, 10%, and 〈5%, respectively, were selected to investigate the spatial variation of soil nutrients in Tarnarix ramosissirna nebkhas and interdune areas in a Qira oasis-desert ecotone at the southern tim of the Taklimakan desert. Soil samples from two layers （0--10 cm and 10-20 cm） of the nebkha and interdune in the four plots were collected for analysis of the litter, soil organic matter, total N, total P, total K, available N, available P, and available K content. The following results were obtained： First, with decreasing vegetation cover from Plot 1 to Plot 4, litter content, soil organic matter content, total N content, total K content, and available K content in the top （0--10 cm） layer of the nebkhas decreased by 69.3%, 37.0%, 35.3%, 8.3%, and 24.5%, respectively. The available N and available P content decreased at first, and then increased with decrease in vegetation cover, while total P content showed no obvious change. Second, the litter content, soil organic matter content, total N content, total P content, available N content, available P content, and available K content in the top layer first decreased, and then increased from under shrub to the margin of the nebkha, to the interdune, to the leeward shadow. The maximum values were mainly found under shrub, while the minimum values were mainly found in the interdune regions. For each soil nutrient index, there was no significant difference between the four positions in Plot 4 （vegetation cover is 〈5%）. Third, compared with the top soil layer, there was a significant reduction in litter content, organic matter content, total N content, total P content, total K content, available P content, and available K content in the bottom （ 10--20 cm） soil layer. The above corresponding mean values were lower by 40.0%, 27.0%, 25.0%, 4.5%, and 2.0%, respectively, while total K content, available N content, and available K content were higher by 4.8%, 103.3%, and 12.1%, respectively. With decreasing vegetation coverage, the changes in soil nutrient content in the two soil layers showed a consistent trend. Fourth, in non-desertified and lightly desertified areas of the oasis-desert ecotone, the biological feedback of shrubs led to obvious nutrient enrichment effects around them. However, as the total vegetation cover decreased and the intensity of desertification increased, non-biological factors began to play leading roles, and the nutrient enrichment effects of shrubs tended to disappear gradually.