Interactive Effects of Carbon and Nitrogen Fixation in Two Biocrust Types in the Mu Us Sandland

Abstract

As early colonizers in dryland ecosystems, biocrusts play a critical role in soil carbon and nitrogen cycling, which was significantly influenced by climate change. Understanding the interactive effects of carbon and nitrogen fixation in biocrusts at a regional scale is crucial for assessing the impacts of climate change on desert ecosystems and supporting effective conservation efforts. In this study, we selected three representative sites across a precipitation gradient (262–476 mm) from west to east in the Mu Us Sandland to measure carbon and nitrogen components, microbial diversity, and functional genes related to carbon and nitrogen fixation in the biocrust layer and underlying soil of moss and cyanobacteria crusts. Our findings showed that carbon and nitrogen components exhibited distinct spatial patterns across the Mu Us Sandland, characterized by higher dissolved (361.52 mg kg-1) and particulate organic carbon (8.41 mg kg-1) in eastern biocrusts and elevated nitrate-nitrogen (3.68 mg kg-1) in western regions. Vertically, biocrust layers showed enhanced carbon and nitrogen contents compared to underlying layers, with specific variations in cyanobacteria crusts. The carbon-nitrogen coupling displayed asymmetric patterns with a goodness of fit of 0.806 for moss crust and 0.701 for cyanobacteria crust, where nitrogen components positively influenced carbon components, evidenced by R² values of 0.949 for moss crust and 0.850 for cyanobacteria crust, despite the absence of significant correlations between carbon fixation genes and nitrogen components. Moreover, these spatial and coupling patterns were driven by key microbial taxa (Cyanobacteria, Bacteroidetes, and Proteobacteria), which enhanced carbon and nitrogen fixation gene abundance, subsequently promoting microbial biomass growth and activating related functional genes. This study highlights the role of precipitation in shaping carbon and nitrogen cycling of biocrusts on a regional scale, providing insights into the interactive processes governing their cycles.

Keywords: Biocrusts, Carbon cycle, nitrogen cycle, interaction effect, Mu Us Sandland