[Response of biocrust-soil system respiration to winter low temperature and simulated warming]

To study the effects of low temperature and simulated warming on respiration of biocrust-soil systems, intact soil columns covered by two dominant types of biocrusts (moss and algae-lichen crusts), were collected in a natural vegetation area in the southeast fringe of the Tengger Desert. Automated soil respiration system (Li-8150) was used to measure respiration rates in biocrust-soil systems under warming (by placing them in an open top chamber) and non-warming treatments in winter (from November 2015 to January 2016). During the whole observation period, soil respiration rates covered by moss crusts were significantly higher than those covered by algae-lichen crusts, which were -0.052 to 0.418 and -0.032 to 0.493 μmol·m^-2·s^-1, respectively. The respiration rates of the two types of biocrust-soil systems showed significant positive linear correlations with soil temperature and volumetric soil water content at 5 cm depth. Through speeding-up the evaporation rates of soil moisture, imitated warming in winter impeded respiration rates of the two biocrust-soil systems. During the whole observation period, the cumulative carbon (C) release by moss crust-soil system (9.90 g C·m^-2) was dramatically higher than that of algae-lichen crust-soil system (7.00 g C·m^-2). The cumulative C release by the biocrust-soil systems in this region in winter was 7.40 g C·m^-2, thus comprising an important part of annual C budget in the desert ecosystems.