Carbon flux in deserts depends on soil cover type: A case study in the Gurbantunggute desert, North China

Carbon flux represents carbon uptake from or release to the atmosphere in desert ecosystems, yet the changing pattern of carbon flux in desert ecosystems and its dependence on soil cover type and rainfall amount are poorly understood. We measured net carbon fluxes (NCF) in soil with four cover types (moss crusted soil, cyanobacteria/lichen crusted soil, bareland and semishrub Ephedra distachya-inhabited site) from April to October of 2010 and 2011, and NCF and dark respiration (DR) after four rainfall amounts (0, 2, 5, and 15 mm) in cyanobacteria/lichen crusted soil, bareland and the E. distachya-inhabited site. NCF in the E. djstachya-inhabited site differed significantly from those of the other three soil cover types, while no difference was observed between the moss and cyanobacteria/ lichen crusted soils or between the two crusted soils and bareland on most measurement occasions. NCF ranged from 0.28 +/- 0.14 to 1.2 +/- 0.07 mu mol m(-2) s(-1) in the biologically crusted soils, and from 2.2 0.27 to 0.46 0.03 mu mol IT1-2 s(-1) at the E. distachya-inhabited site. Daily NCF in the biologically crusted soils and bareland showed carbon release at most times and total carbon production ranged from 48.8 5.4 gC m(-2) yr(-1) to 50.9 +/- 3.8 gC m(-2) yr(-1), while the E. distachya-inhabited site showed a total carbon uptake of 57.0 +/- 9.9 gC m(-2) yr(-1). Daily variances in NCF were well-explained by variances in surface soil temperature, and seasonal NCF showed a significant linear relationship with soil moisture in the two biologically crusted soils and bareland when soil volumetric water content was less than 3%. Rainfall elicited intense carbon release in cyanobacteria/lichen crusted soil, bareland and at the E. distachya-inhabited site, and both NCF and DR were positive in the first two days after rainfall treatments. Mean NCF and DR were not different between rainfall amounts of 2, 5 and 15 mm in cyanobacteria/lichen crusted soil and bareland, while they were significantly higher after 15 mm rainfall treatment compared with 2 mm and 5 mm treatments at the E. distachya-inhabited site. Mean NCF and DR in the first two days increased logistically with rainfall amount. Based on our findings, we suggest that E. distachya-inhabited sites contribute to carbon uptake in the Gurbantunggute Desert, while biologically crusted soils exhibit carbon release for most of the year. Even though photosynthesis immediately following rainfall can be stimulated, carbon uptake effect in biologically crusted soil is likely intermittent and confined to periods when moisture is available. (C) 2012 Elsevier Ltd. All rights reserved.