干旱区生态环境知识资源中心

Nitrogen fixation is generally considered to play a major role in nitrogen assimilation in desert soils, arid the Nitrogen-Efficient Guild (NEG) is a useful index of the freeliving nitrogen fixer population. Nitrogen-Efficient Guild dynamics in macrophytic patches in the Negev Desert probably contribute to the understanding of nitrogen processes in desert ecosystems. It is also important to determine the relationship between the Nitrogen-Efficient Guild numbers and nutrient availability on a tempospatial dynamic basis. This study was conducted in the Negev Desert during a period of one year. During this time, the Nitrogen-Efficient Guild number fluctuated between 3.9 +/- 0.7 x 10(6) and 28.5 +/- 5.3 x 10(6) colony forming units (CFU) g(-1) in a loessial soil site, and 0.7 +/- 0.2 x 10(6) and 10.7 +/- 11.8 x 10(6) in a sandy soil site, with significant peal: values (P < 0.05) during the winter season. The results demonstrate that significantly larger populations of free-living nitrogen fixers exist in soils under shrub canopies, suggesting considerable nitrogen fixation ability. It seas also concluded that the nitrogen fixing populations and communities vary with seasons in the desert, since they are mainly controlled by soil moisture. Furthermore, the Nitrogen-Efficient Guild numbers exhibit a significant correlation with total organic carbon arid total soluble nitrogen, but riot with dissolved organic carbon.