Top-down effects on biological soil crust function

Biological soil crusts (BSCs) are communities of microorganisms, mosses, and fungi that control ecosystem functions in drylands. Despite their importance, little is known about how trophic interactions affect BSC function. We conducted a series of mechanistic experiments to tease out the direct (i.e., consumption) and in-direct (i.e., fecal and mucus deposition) pathways by which crustivores (i.e., consume BSCs) and detritivores affect BSC functions- complemented by a manipulative field experiment exploring the integrative effect of these pathways. We showed that detritivore feces, mucus, and grazing increased the BSCs' CO2 respiration. Detritivore feces also increased BSC N content by 9% compared to BSCs not exposed to snail consumers. Crustivorous snail feces increased BSC CO2 respiration, and their mucus decreased BSC %C and %N. In the field, detritivorous and crustivorous snails increased BSC %C by 15% and 17%, respectively, but did not affect BSC CO2 respiration. Combined, our findings highlight that macro-invertebrate consumers exert top-down regulation on BSC function, opening the door for a new avenue of trophic research.

Automated summary

This study explores the impact of trophic interactions on biological soil crusts (BSCs) in drylands. Through experiments and field observations, it is found that detritivores and crustivorous snails have both direct and indirect effects on BSC functions, including increasing CO2 respiration and altering nutrient content. These findings provide new insights into the role of macro-invertebrate consumers in regulating BSC function.