Differentiation of microbial activity and functional diversity between various biocrust elements in a heterogeneous crustal community

Biological soil crusts (BSCs) dominate the interspace between sparse vegetation in arid and cold environments worldwide and fulfill diverse ecosystem functions. Natural BSCs are usually classified as a series of stepwise successional stages along with a gradual improvement of biological properties and micro-environmental conditions. However, the effects of spatial heterogeneity on the ecological traits of BSCs remain largely unknown, especially in the microbial scenario. In this study, three adjacent biocrust elements with different successional levels (cyanobacterial, lichen, and moss crusts) were collected from a continuous and heterogeneous crustal community at small scale (centimetre level) in the Gurbantünggüt Desert, aiming to distinguish the alteration of microbial distribution and functional traits among them. The catabolic fingerprint of sole-carbon induced respiration was measured by MicroResp™ respiration system to calculate the functional diversity indices. Ribosomal copy numbers of different soil microbes (bacteria, fungi, and phototrophs), as a proxy for microbial relative abundance, were analysed through quantitative PCR methods. We also evaluated the related physicochemical parameters. The results show evidences that the microbial abundances and functional traits associated with each biocrust element are inconsistent with its successional level. Although higher microbial activities and more benign soil conditions (increased soil moisture and organic matter) were still found in well-developed moss crust, higher microbial abundances (except fungi) and enhanced functional diversity were observed in less-developed cyanobacterial crust. Spatial heterogeneity due to the jigsaw-like pattern of various biocrust elements partly affects microbial performances in BSCs. More studies focusing on quantitatively measuring spatial arrangement of biocrust elements are needed to clarify the mechanisms underlying to functional differentiation in crustal communities.