Grazing intensity is associated with shifts in nutrient status, metabolite profiles, and selected bacterial taxa in biological soil crusts

Abstract

Grazing can alter bacterial communities by influencing soil properties and metabolites. Nevertheless, metabolites in biological soil crusts (BSCs) under grazing disturbance remain poorly understood. Here, we collected BSC samples under three grazing intensities (0 [enclosure, EN], 1.00 [light grazing, LG], and 2.33 [heavy grazing, HG] sheep-units ha⁻¹ year⁻¹) in the arid region of northwestern China to explore the effects of physicochemical properties and metabolites on bacterial communities. Our results indicated that the number of metabolites decreased with increasing grazing intensity, which markedly altered metabolite composition. Nutrients (NO₃⁻-N and NH₄⁺-N) and the metabolite composition of BSCs were closely correlated with bacterial community composition (p < 0.05). A total of 135, 131, and 124 differential metabolites were identified between the EN and LG, EN and HG, and LG and HG groups, among which organic oxygen compounds, phenylpropanoids and polyketides, and lipids and lipid-like molecules were the major classes. Co-occurrence network analysis revealed significant correlations between major differential metabolites and dominant bacteria (Proteobacteria, Actinobacteriota, and Chloroflexi). These results highlight that nutrients and metabolites in BSCs play important roles in regulating bacterial community composition, providing data support for the conservation and restoration of desert grasslands.

Graphical abstract

Keywords

biological soil crusts / grazing intensity / bacterial community composition / differential metabolites / soil nutrients

Highlight

	● Increasing grazing intensity decreased metabolite count and altered metabolite composition in BSCs.
	● Grazing intensity did not affect bacterial community diversity but induced adaptive shifts in bacterial community composition.
	● BSCs nutrients and metabolites were significantly correlated with bacterial community composition.
	● Abundant differential metabolites occurred across grazing gradients, with the most complex co-occurrence network between enclosure and heavy grazing.

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