Of mammals and bacteria in a rainforest: Temporal dynamics of soil bacteria in response to simulated N pulse from mammalian urine

Abstract

Pulse-type perturbation through excreta by animals creates a mosaic of short-term high nutrient-load patches in the soil. How this affects microbial community composition and how long these impacts last are important for microbial community dynamics and nutrient cycling. Our study focused on the short-term responses to N by bacterial communities and ‘functional groups’ associated with the N cycle in a lowland evergreen tropical rainforest. We applied a single urea pulse, equivalent to urine-N deposition by medium-sized mammals to simulate N enrichment and changes in soil N availability, and analysed soil bacterial communities using molecular methods, before and after urea application. Urea addition increased mineral N availability and changed bacterial community composition, from phylum to operational taxonomic unit levels, however, taxon richness and diversity were unaffected. Taxa involved in the physiologically “narrow” processes of nitrification (e.g. Nitrosospira) and denitrification (e.g. Phyllobacteriaceae, Xanthomonadaceae and Comamonadaceae) increased their relative abundance, while N2-fixers (e.g. Rhodospirillales, and Rhizobiales) decreased after treatment. While a temporal legacy on both community composition and functional group profile was observable 58 and 159 days after treatment, at the latter date bacterial communities were already tending towards pre-treatment composition. We suggest that pulse-type perturbation by mammal urine that occurs on a daily basis has strong short-term effects on patch dynamics of soil microbiota and N availability. Such a spatio-temporally dynamic soil environment enhances overall microbial richness and diversity, and contributes to the apparent temporal resilience of community composition. A plain language summary is available for this article.