Ecophysiological and biochemical responses of desert moss Syntrichia caninervis to changes of snow depth in four years

Winter snowfall, as the main form of precipitation in Gurbantunggut Desert, plays an important role in the stability and development of biological soil crust（BSCs）. The pattern of snow cover in winter has changed greatly due to continuous global warming and frequent occurrence of extreme climate events. As an important component of soil crusts, it is not clear how desert mosses respond to long-term snow depth changes at physiological and biochemical levels. In this study, four snow gradients, including snow removal（-S）, ambient snow（S）, double snow（2S） and triple snow（3S） were set up in the field, to investigate the physiological and biochemical characteristics of Syntrichia caninervis after four years of snow depth change. The results showed that the change of snow depth significantly affected plant water content, the maximum photochemical efficiency（Fv/Fm）, the effective photochemical quantum yield of PSII（Y（II））, osmotic regulation substance content and antioxidant enzyme activity. Compared with the treatment of removing snow, the water content, Fv/Fm and Y（II） of Syntrichia caninervis increased with the increase of snow depth, however, the contents of free proline, soluble protein, soluble sugar, malondialdehyde（MDA） and activities of superoxide dismutase（SOD）, peroxidase（POD） and catalase（CAT） showed a decreasing trend. Correlation analysis showed that Fv/Fm and Y（II） of Syntrichia caninervis were significantly positively correlated with soil temperature and plant water content, while soluble protein, soluble sugar, MDA content, SOD, POD and CAT activities were significantly negatively correlated with soil temperature and plant water content. Notably, 3S increase in snow cover for 4-year have significantly decreased Y（II） and increased MDA content of Syntrichia caninervis compared with natural snow cover. These results indicated that snow cover has created a suitable habitat for Syntrichia caninervis, and reduced the degree of drought and cold stress of Syntrichia caninervis. However, the growth of the Syntrichia caninervis would be negatively affected by both long-term snow accumulation and long-term snow reduction.