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Biocrusts play an important role in carbon (C) assimilation in arid and semiarid regions. In order to assess C gain in the crusted Hallamish dune field, net photosynthesis (Pn) and respiration (R) were measured at five crust types (A-E) which show a gradual increase in their chlorophyll content (with A < B < C < D < E). Pn and R were calculated per chlorophyll a and b (hereafter a/b) content. Total C input was calculated based on a large database that includes data on the temporal change in the chlorophyll content during the winter growing season, annual daylight and nighttime wetness duration and the cover of each crust type. The data show high similarity of Pn and R per chlorophyll content for all crusts (0.9-1.1 and 0.5-0.6 gC (Chla/b)(-1) h(-1), respectively). Both Pn and R showed a gradual increase with chlorophyll content with A approximate to B < C < D < E, with Pn ranging between 0.0311 (for crust A) and 0.1784 (for crust E) gC m(-1) h(-1). Total calculated C gain for crusts A-E assuming total crust cover ranged between 2.1-8.6 gC m(-2) a(-1) for crusts A-D and 50.90 gC m(-2) a(-1) for crust E, with total annual input into the crusted areas of the ecosystem and the entire ecosystem being 3.7 and 23 gC m(-2) a(-1), respectively. In comparison to net ecosystem C exchange (NEE) from arid regions, our findings highlight the important role played by biocrusts in CO2 sequestration and as C provider for an extreme arid ecosystem. Yet, although a conservative approach was adopted, the data should be regarded as rough estimation only. In-situ field measurements are still required in order to substantiate the crust role in the annual C gain. (C) 2015 Elsevier B.V. All rights reserved.