Fine roots are the dominant source of recalcitrant plant litter in sugar maple-dominated northern hardwood forests.

Mengxue Xia,Alan F Talhelm,Kurt S Pregitzer

doi:10.1111/nph.13494

Abstract

Summary Most studies of forest litter dynamics examine the biochemical characteristics and decomposition of leaf litter, but fine roots are also a large source of litter in forests.We quantified the concentrations of eight biochemical fractions and nitrogen (N) in leaf litter and fine roots at four sugar maple (Acer saccharum)‐dominated hardwood forests in the north‐central United States. We combined these results with litter production data to estimate ecosystem biochemical fluxes to soil. We also compared how leaf litter and fine root biochemistry responded to long‐term simulated N deposition.Compared with leaf litter, fine roots contained 2.9‐fold higher acid‐insoluble fraction (AIF) and 2.3‐fold more condensed tannins; both are relatively difficult to decompose. Comparatively, leaf litter had greater quantities of more labile components: nonstructural carbohydrates, cellulose and soluble phenolics. At an ecosystem scale, fine roots contributed over two‐thirds of the fluxes of AIF and condensed tannins to soil. Fine root biochemistry was also less responsive than leaf litter to long‐term simulated N deposition.Fine roots were the dominant source of difficult‐to‐decompose plant carbon fractions entering the soil at our four study sites. Based on our synthesis of the literature, this pattern appears to be widespread in boreal and temperate forests.

Highlights

Plant litter decomposition drives major flows of carbon (C) in soil systems: C mineralization and C storage (Chapin et al, 2011)
We investigated the abundance of eight major biochemical fractions, N concentration and three litter quality indices for leaf litter and fine roots collected from four sugar maple-dominated hardwood forests in the north-central United States
The amount of unidentified material was generally higher in leaf litter than in fine roots, a trend that was strongest at site C

Summary

Introduction

Plant litter decomposition drives major flows of carbon (C) in soil systems: C mineralization and C storage (Chapin et al, 2011). Plant litter is derived from various plant organs, such as leaves (Aber & Melillo, 1982), roots (Gill & Jackson, 2000) and woody stems (Dearden et al, 2006). Of these organs, decomposition research has primarily focused on leaf litter, likely because leaf litter is a large and visible input to the soil that can be sampled. Leaf litter decomposition processes, including the rate, chemistry and biology of decomposition, are often assumed to be broadly representative of plant litter decomposition (Rasse et al, 2005; Freschet et al, 2013) This assumption has been used extensively in models of ecosystem C cycling (Schmidt et al, 2011)

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