Disentangling the relative importance of precipitation, biocrust succession, and shrub cover in mediating soil phoD-harbouring communities and organic phosphorus mineralisation

Biological soil crusts (biocrusts) are crucial components of dryland ecosystems worldwide; however, their roles in phosphorus (P) transformation and associated functional communities have received less scientific attention compared with carbon (C) and nitrogen (N) cycling. Currently, little is known about the relative importance of precipitation, biocrust succession, and shrub cover in mediating soil P transformation. Here, we conducted a broad field survey across deserts in Northern China to investigate the roles of these factors in soil organic P (Po) mineralisation. We examined various P mineralisation parameters, including soil C:P ratio, soil Po content, bioavailable P, alkaline phosphatase (ALP)-encoding gene phoD abundance, and ALP activity. Additionally, we investigated the diversity and composition of soil phoD-harbouring communities and their relationships with Po mineralisation. Overall, the P mineralisation parameters increased with biocrust succession, and their responses to precipitation levels varied and were contingent upon the biocrust successional stages, while less significant differences were observed between the presence and absence of shrub cover. Most P mineralisation parameters were positively correlated within individual deserts or across all deserts studied. Moreover, the beta diversity, rather than the alpha diversity, of soil phoD-harbouring communities predominantly drove Po mineralisation. The abundance of certain genera (Actinoplanes and Micromonospora) that were relatively less dominant but showed significant positive correlations with P mineralisation parameters. By highlighting biocrust succession as the key determinant of soil Po mineralisation, the significance of precipitation and biocrust succession on phoD-harbouring communities, as well as the prevalence of community beta diversity in driving soil Po mineralisation, this study provides novel insights into the mechanisms underlying the transformation of Po into bioavailable P in biocrust systems.