古尔班通古特沙漠土壤水分与化学性质的空间分布

区域尺度上,气象和水文状况是影响植被分布格局和土壤性状的主要因子,当然,局部的地貌特征及植被分布对土壤性质的影响也是不能忽视的。以古尔班通古特沙漠为研究对象,对其南缘至腹地约25 km的土壤水分与化学性质的空间分布及其相互关系进行研究,结果显示:水平方向上,从沙漠南缘至腹地,土壤水分在丘底呈减小趋势,尤其是距边缘10 km以外,且在距边缘6—7 km出现1个峰值。同时土壤pH值和电导率的大小以及有机碳,全氮,有效氮,全磷和有效磷含量与土壤水分的变化状况相似,在丘底呈减小趋势,而在丘坡和丘顶上均呈波动分布。这说明丘底土壤性质的空间格局受到气象和水文状况的显著影响,而丘坡和丘顶土壤性质并没有受到气象和水文状况的显著影响,这种波动分布主要由采样点的设置及植物的分布状况所引起。丘底土壤水分及化学性质均显著高于丘坡和丘顶,这说明地貌特征对土壤性质的空间分布有显著影响。垂直方向上,不同深度土层土壤性质也存在显著差异,土壤水分,pH值和电导率随着土层深度增加而增加,而土壤养分随土层深度增加而减小。相关分析结果表明:仅4、5月份的土壤含水量及年平均土壤含水量与丘底土壤化学性质显著正相关,这可能由于冬季积雪的融化导致了土壤水分在4、5月份的聚集比较明显,使土壤水分对土壤化学性质发挥作用。总之,土壤空间异质性是由气象和水文以及地貌特征共同影响的,而土壤空间异质性的变异进而影响到植被的分布,植被的分布反过来又影响土壤的空间分布,因此土壤的空间分布和植被的空间分布是相互影响,共同作用的。

Spatial pattern for soil water and chemical properties in Gurbantunggut Desert

Spatial heterogeneity is considered as a ubiquitous feature in natural ecosystems. It is also well known that soil heterogeneity is a basic element for competitive and/or facilitative for resources competitive and interactions between plants, especially in the stressed environments of arid shrub-desert and steppe ecosystems. Consequently, soil spatial heterogeneity may determine the occurrence of plants, structure of vegetation and pattern of landscapes, and greatly affect biogeochemical cycles. At the regional or landscape scale, climatic and geomorphologic factors often exert strong influences on the soil spatial heterogeneity, however, local-scaled topography and vegetation should not be ignored because they are important factors in the formation of small-scaled landscape patterns. This study was designed to investigate the spatial pattern of soil water and chemical properties and their relationship in Gurbantunggut Desert ranged from the south fringe to the hinterland of about 25 km. The results showed that soil water and soil chemical properties presented a decreasing trend from the south fringe to the hinterland at the interdune, especially at about 10 km away from the south fringe, e.g., a significant peak value was appeared at the distance of 6-7 km away from the fringe. However, it was a fluctuated pattern at the slope and top dune; it indicated that climatic and geomorphologic factors exerted strong influences on the spatial heterogeneity of soil at the interdune, but not on the slope and top dune. This phenomenon can be explained as the significant decreasing of groundwater level and precipitation from the south fringe to the hinterland. In addition, soil water and chemical properties were significantly higher at the interdune than they were at the slope and the top dune, since the local topographic conditions resulted in water and soil accumulating significantly at the interdune compared to the slop and the top dune. Furthermore, soil water and chemical properties at different soil depth were significantly different, soil water content, pH and electrical conductivity increased with the soil depth, while soil nutrients content decreased with the soil depth. It indicated soil salinity and soil nutrient status behaved differently in spatial heterogeneity, with an inverse distribution between soil nutrients and soil salinity/alkalinity at different soil depth. Correlation analysis also confirmed that soil water and chemical properties were significantly correlated at the interdune in April, May and annual averaged period. It further documented that climatic and geomorphologic factors exert strong influences on the spatial heterogeneity of soil, especially since topography is the most important factor for the spatial pattern in soil properties at Gurbantunggut Desert, which lead to soil water and soil recourses accumulated significantly at the interdune in April and May. In summary, our results showed that within a population or community and over tens of kilometers, soil spatial heterogeneity was caused by climatic, geomorphologic (abiotic) and dominant plant types (biotic) together. However, these biotic and abiotic factors were not absolutely separated, but inter-linked each other, i.e., plant-soil interactions. The spatial heterogeneity of abiotic factors determined the spatial patterning of biotic factor, conversely, spatial patterns of plant distribution influenced rates of soil physical and biogeochemical processes.