How Does Soil Spatial Variation Depend on Scales in a Temperate Desert

Spatial heterogeneity of soil resources is recognized as a common feature in natural ecosystems, and spatial heterogeneity has long been considered to be a major driver of biological processes and a basic element of both competitive and facilitative biological interactions. Consequently, heterogeneity may determine the occurrence of plants, structure of vegetation, and pattern of landscape, and greatly affect biogeochemical cycles in many ecosystems. Many studies have shown that the spatial heterogeneity of soil exists at scales ranging from the rhizosphere to the landscape or region. However, the scale at which this spatial heterogeneity is most significant and the most important factor to express this heterogeneity are still not known.

The researches hypothesized that the heterogeneity might exist at scales from the rhizosphere to landscape (i.e. from individual plant to population or community to ecosystem) in the Gurbantunggut Desert, a largest temperate desert in China. Then, they took the soil samples in the desert at the different scales, the fine scales (10^-3-10^-1), the intermediate scales (10⁰-10²,) and the landscape scales (10³-10⁴m), and measured the soil chemical properties, including pH, electrical conductivity (EC), organic carbon, total nitrogen, available nitrogen, total phosphorus, and available phosphorus were considered in the investigation.

The results show that at the scale of individual plant (10^-1 m), significant enrichment of soil resources occurred under shrub canopy and “fertile islands” formed in the desert ecosystem. Soil EC exhibited the largest heterogeneity at this scale, indicating that individual plants exerted a great influence on soil salinity/alkalinity. Soil nutrients exhibited the greatest heterogeneity at the scale of sand dune/interdune lowlands (between communities, 10² m). The main important factors contributing to soil spatial heterogeneity in the Gurbantunggut Desert were individual plants and different topographic characteristics, namely, the appearance of vegetation, especially shrubs or small trees, and existing sand dunes. The results fund that soil salinity/alkalinity and soil nutrient status behaved differently in spatial heterogeneity, with an inverse distribution between them at the individual scale.

The study indicated that the results would help us further understand the dependence of heterogeneity of arid ecosystems on scale and the driving forces behind this dependence and also aid in the design of soil sampling strategies in arid lands, for example, using intensive sampling at a scale with larger soil spatial variation such as the individual or topographic scale, but sparse sampling at a scale with smaller soil spatial variation. The study was published in Pedosphere in June 2014.