Universal microbial reworking of dissolved organic matter along soil gradients

Abstract

Soils are losing increasing amounts of carbon annually to freshwaters as dissolved organic matter (DOM), which, if degraded, can offset their carbon sink capacity. However, the processes underlying DOM degradation across environments are poorly understood. Here we show DOM changes similarly along soil-aquatic gradients irrespective of environmental differences. Using ultrahigh-resolution mass spectrometry, we track DOM along soil depths and hillslope positions in forest catchments and relate its composition to soil microbiomes and physico-chemical conditions. Along depths and hillslopes, we find carbohydrate-like and unsaturated hydrocarbon-like compounds increase in abundance-weighted mass, and the expression of genes essential for degrading plant-derived carbohydrates explains> 50% of the variation in abundance of these compounds. These results suggest that microbes transform plant-derived compounds, leaving DOM to become increasingly dominated by the same (ie, universal), difficult-to-degrade compounds as degradation proceeds. By synthesising data from the land-to-ocean continuum, we suggest these processes generalise across ecosystems and spatiotemporal scales. Such general degradation patterns can help predict DOM composition and reactivity along environmental gradients to inform management of soil-to-stream carbon losses.

Publication
Nature Portfolio
Erika C. Freeman
Erika C. Freeman
Ph.D. Student, University of Cambridge

NA

Erik J.S. Emilson
Erik J.S. Emilson
Research Scientist, Watershed Ecology Team Lead, Associate Editor CJFR

I am interested in how forests support freshwater ecosystem services. My research combines microbial and molecular approaches to undertand how forest productivity and disturbances affect ecosystem functions in headwater streams and lakes.

Caroline Emilson
Caroline Emilson
Forest Ecologist and Bioinformatician

Ecologist specializing in environmental genomics and microbial ecology.