The Science

Peatland ecosystems are important for terrestrial carbon (C) and nitrogen (N) cycling, occupying 3% of the Earth’s land surface yet storing approximately 25% of terrestrial C as recalcitrant organic matter. Sphagnum peat moss is responsible for much of the primary production and produces recalcitrant organic matter in these ecosystems, but its growth and productivity depend on symbiotic association with various microbes. Sphagnum species are known to exchange C-rich carbohydrates for N-rich molecules produced by symbiotic cyanobacteria, but this conceptual model may overlook a key role for sulfur (S). Using synchrotron-source microprobe techniques, the team determined that Sphagnum angustifolium colonization by Nostoc muscorum resulted in an enrichment of total S and increases in sulfate compounds relative to reduced S and sulfonate in plant tissues. At the scale of individual hyaline cells, colonized cells exhibited localized enrichment of reduced S surrounded by diffuse sulfonate, similar to observations of isolated N. muscorum colonies. Results suggest that colonization stimulates plant S uptake and production of S-containing metabolites that may be converted into reduced S metabolites by cyanobacteria.

The Impact

This study indicates that Sphagnum may generate oxidized S compounds to exchange for N-rich metabolites produced by cyanobacteria, highlighting an important role for S in peatland biogeochemistry.

Summary

Researchers evaluated how S. angustifolium colonization by N. muscorum modifies S abundance and speciation at the scales of individual cells and across whole leaves. This mutualistic relationship may result in at least temporary increases in oxidized S compounds within Sphagnum tissues that subsequently undergo anaerobic decomposition in saturated peat soils. Additional studies are needed to determine the role of S exchange in driving ecosystem-scale S, N, and C dynamics.

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