Nitrogen Fixation in Biological Soil Crusts from the Tengger Desert

Nitrogen fixation is widespread in desert ecosystems. To date, desert nitrogen fixation has been studied mainly in arid areas which are located at the margins of deserts, while the knowledge on desert soil micro-organisms remains fragmentary, especially in the biological soil crusts in arid and semiarid areas. The nitrogen fixation functions of biological soil crusts (BSCs) have recently been recognized as an important N source in arid and semiarid regions. It is important to study the nitrogen fixation characteristics in an artificially re-vegetated desert ecosystem, because the nitrogen fixation of BSCs influences not only the soil restoration in desert, but also nitrogen content in plants. The northeastern part of the Tengger Desert was once mobile sand dunes. After installing straw checkerboards and planting xeroic shrub species in 1950s, three types of BSCs, moss crusts, lichen crusts, and cyanobacterial-algal crusts, were found within these re-vegetated areas.

The researchers from Key Laboratory of Biogeography and Bioresource in Arid Land, Xinjiang Institute of Ecology and Geography, and Shapotou Desert Research and Experiment Station, Cold and Arid Regions Environmental & Engineering Research Institute, Chinese Academy of Sciences, used the ecological, chemical and statistical methods to study the nitrogen fixation in BSC. They found that the nitrogenase activity of BSCs ranged from 2.6 to 16.6 mmol m-2 h-1 in the Tengger Desert, and nitrogenase activity was dependent on crust type, precipitation, and temperature, but not on irradiance. Cyanobacterial-algal crusts showed the highest nitrogenase activity (16.6 mmol m-2 h-1), followed by lichen crusts (6.9 mmol m-2 h-1), and moss crusts (2.6 mmol m-2 h-1). Cyanobacterial-algal crusts demonstrated maximum nitrogenase activity with the precipitation of 1.54 mm, while the maximum activity for lichen and moss crusts occurred at 1.83 mm and 0.65 mm, respectively. The potential nitrogen input was estimated to be 3.7-13.2 g m-2 a-1, and the high nitrogen fixation in this region resulted from the perfect match of optimum climate to the favorable environmental factors for BSC nitrogenase activity. The study demonstrated that BSCs are the main nitrogen input source in the temperature desert ecosystem.

This study was supported by the National Natural Science Foundation of China (41001067, 40930636 and 40825001). The related paper was published in European Journal of Soil Biology, 2011, 47(3): 182-187. doi:10.1016/j.ejsobi.2011.04.001. The article can be linked as follows: http://www.sciencedirect.com/science/article/pii/S1164556311000227.