Carbon fixation by biological soil crusts following revegetation of sand dunes in arid desert regions of China: A four-year field study

Biological soil crusts (BSCs) are important sources of carbon input to ecosystems in arid and semiarid regions, where vascular plants are restricted by the rigorous environment and limited soil water. Sand dune stabilization by revegetation can enhance colonization and development of BSCs on sandy soil surfaces, and convert BSCs from the early successional stage dominated by cyanobacteria and algae to the later stage dominated by lichens and mosses. This study estimated the carbon fixation by two successional stages of BSCs based on four years of field observations. Carbon fixation by two BSCs has been compared via estimating daily carbon fixation using measuring net photosynthesis with ten sampling plots per crust stage in situ, combining with calculating the wet daytime of crustal cryptogam thallus. However, diurnal carbon fixation of both BSCs was largely determined by crustal water content rather than photosynthesis photon flux and temperature. The range of optimal gravimetric water content for early BSCs was 1-3.5%, and 1-5% for the later BSCs. The annual carbon fixation was 11.36 g C m(-2) yr(-1) for cyanobacteria-algae dominated crusts and 26.75 g C m(-2) yr(-1) for lichen-moss dominated crusts. The latter had a higher carbon input due to a higher water-holding capacity, prolonging wet daytime and higher chlorophyll content, as well as higher light capture. These findings indicate the recovery of BSCs is expected to significantly increase carbon input into sandy desert ecosystems. (c) 2012 Elsevier B.V. All rights reserved.