Organic matter decay response to root functional types and simulated sea-level rise in a temperate salt marsh

Abstract

<p>Salt marshes are carbon rich ecosystems, but they are threatened by sea-level rise. Root litter dynamics have been little studied, despite contributing three times more to carbon burial than leaves litters and being important for salt marsh resilience to sea level rise. Root litter is defined as one single pool in salt marshes, yet this approach might fail to accurately assess root litter decay, as shown in terrestrial ecosystems where a root functional framework proved to be more accurate. We investigated if root functional types (fine absorptive roots, fine transportive roots and rhizomes) and inundation duration affected OM decay rate in a temperate salt marsh. We used a marsh organ and litterbags.We found that the decay rate strongly varied between root functional types, with fine absorptive roots decaying 30% slower than fine transportive roots and 14% slower than rhizomes.The decay rate was poorly explained by C:N ratio, N and C contents, while better correlated with root lignin composition. The duration of inundation had little effect on the belowground OM decay and did not interact with the decay of root functional types. Therefore, a shift toward experimental methods separating roots by function seems necessary to accurately assess the contribution of root litter to carbon burial in salt marshes. Overall, our results suggest that the current global carbon decay of salt marshes may have been overestimated and that fine absorptive roots could be a larger source for carbon burial than previously thought in salt marshes.</p>