Dynamics of the Nitrogen-Efficient Guild and its relationship to nitrogen and carbon patterns in two desert soil ecosystems

Nitrogen fixation is generally considered to play a major role in nitrogen assimilation in desert soils, and the Nitrogen-Efficient Guild (NEG) is a useful index of the free-living 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 × 10⁶ and 28.5 ± 5.3 × 10⁶ colony forming units (CFU) g^-l in a loessial soil site, and 0.7 ± 0.2 × 10⁶ and 10.7 ±1.8 × 10⁶ in a sandy soil site, with significant peak 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 was 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 and total soluble nitrogen, but not with dissolved organic carbon.