Snail mucus increases the CO2 efflux of biological soil crusts

Biological soil crusts (hereafter, biocrusts) are communities of
microorganisms that regulate key ecosystem processes such as water
distribution, soil erosion, and nutrient cycling in drylands worldwide.
The nature of biocrust function can be influenced by multiple
environmental factors, including climatic conditions (e.g.,
precipitation), interactions with plants, and anthropogenic disturbances.
Animal regulation of biocrust function has received less research
attention, focusing primarily on livestock trampling and to a much lesser
extent on biocrust consumption by mesofauna. Deposition of animal waste
products, carcasses, and other body secretions such as mucus may also
affect biocrust function. Yet, this novel regulatory pathway, to our
knowledge, has never been empirically tested. Our goal was to begin
bridging this knowledge gap by exploring how snail mucus affects biocrust
CO2 efflux— using two distinct biocrust communities and three snail
species. We found that snail mucus increased the CO2 efflux of both
cyanobacteria- dominated and lichen/moss- dominated biocrusts. However,
the magnitude of snail mucus effects on biocrust CO2 efflux varied between
snail species— possibly due to species-level differences in snail diet.
Our study highlights a novel interaction between animals and biocrusts and
suggests that even small quantities of animal-derived nutrients can have
important consequences for biocrust carbon dynamics. Manuscript Highlights
Mucus increased the CO2 efflux of cyanobacteria-dominated biocrusts by
>20%. Mucus enhanced the CO2 efflux of moss/lichen-dominated
biocrusts by > 86%. Dietary differences likely underlie
species-specific effects of mucus on biocrusts.