Abstract: Taking the soil algal and moss crusts in natural and revegetated areas at the southeast edge of Tengger Desert as test objects and by using different types of OTC, this paper studied the nitrogen-fixing activities of the crusts under effects of wintertime low temperature and simulated warming. In the OTCs, the increment of wintertime daily air temperature was about 1 ℃, and that of the soil temperature at different depths was about 3.2 ℃. During the experimental period, the average nitrogen-fixing activity of algae crust was 1.2×10⁴ nmol C₂H₄·m^-2·h^-1, which was significantly higher than that of moss crust (0.4×10⁴ nmol C₂H₄·m^-2·h). The nitrogen-fixing activities of algal and moss crusts were significantly positively correlated with the air temperature in whole experimental period, and with the precipitation amount three days before the experiment. Under the low temperature, wet, and freezing conditions in wintertime, the damaged nitrogen-fixing enzyme system because of the intracellular ice formation of crust organisms could be the main reason for the decline of the crust’s nitrogen-fixing activities, while warming could promote the crust’s nitrogen-fixing activities. Our study suggested that under the background of future global warming and precipitation pattern change, the increase of air temperature in wintertime could promote the nitrogen contribution of soil biocrusts to arid area ecosystems.

Key words: tasseling stage, root lodging, stem lodging, yield loss, summer maize.