Impacts of litter decay on organic leachate composition and reactivity

Abstract

Litter decomposition produces labile and recalcitrant forms of dissolved organic matter (DOM) that significantly affect soil carbon (C) sequestration. Chemical analysis of this DOM can provide important knowledge for understanding soil DOM dynamics, but detailed molecular analyses on litter derived DOM are scarce. Here we use ultrahigh resolution mass spectrometry (FT-ICR MS) to characterize the molecular composition of DOM from fresh and progressively decomposed litter samples. We compared high reactive (HR) and low reactive (LR) litter sources with regard to changes in the chemistry and bioavailability of leachates throughout the early phase of litter decay. We show that litter reactivity is a driver of chemical changes in the leached DOM of litter species. Birch, alder and Vaccinium (i.e. HR) litter initially produced more DOM with a higher lability than that of spruce, pine and wood (i.e. LR) litter. Labile oxidized phenolic compounds were abundant in leachates produced during the initial HR litter decay stages, indicating litter lignin degradation. However, the similarity in chemistry between HR and LR leachates increased during the litter decay process as highly leachable structures in HR litter were depleted. In contrast, chemistry of leachates from LR litter changed little during the litter decay process. The oxygenated phenolic compounds from HR litter were driving the lability of HR leachates and the changes in relative abundance of molecules during DOM incubation. This appeared to result in the creation of stable aliphatic secondary microbial compounds. In LR leachates, lability was driven by labile aliphatic compounds, while more resistant phenolic compounds were associated with recalcitrance. These results show how DOM dynamics follow different paths depending on litter reactivity, which has important implications for soil biogeochemistry and C sequestration.

From canopy to consumer: what makes and modifies terrestrial DOM in a temperate forest

“…Microbial degradation homogenizes tree DOM sources and resolves soil DOM sources In this study, DOM from diverse tree sources became more similar with microbial processing (Fig. 4a), as observed during the microbial buffering and compositional convergence previously proposed to decrease the diversity of plant leachate DOM (Harfmann et al 2019;Hensgens et al 2021). This contrasts with the soil leachate final time points, which progress towards the outside of PC1, separating from the initial time points as microbially degraded soil DOM became more diverse (Fig.…”

Linking Dissolved Organic Matter Composition to Landscape Properties in Wetlands Across the United States of America

“…In contrast, molecular formulae that are more abundant in porewaters follow a more Gaussian distribution centered on medium masses and are shifted to lower O/C values with greater diversity of N‐ and S‐containing formulae (Figures 5d and 5e). These formulae are likely sourced from microbial exudation and continuous degradation of soil and plant‐derived biopolymers (Lehmann & Kleber, 2015), both of which have been shown to afford similar DOM compositions (Hensgens et al., 2021; Roth et al., 2019).…”

“…Aquatic DOM represents a mixture of organic molecules from both terrestrial and internally produced sources and contains distinct chemical features that contribute to its function in aquatic ecosystems (Hansen et al., 2016; Kellerman et al., 2018; Rossel et al., 2013). For instance, DOM originating from fresh vegetation and algal biomass is considered highly biolabile on short timescales, while DOM that is more aromatic or has undergone extensive processing is typically less biolabile and respired over longer time scales (Guillemette et al., 2013; Hansen et al., 2016; Hensgens et al., 2021). In contrast, highly aromatic DOM is susceptible to photomineralization, which may degrade larger aromatic structures and produce smaller, more aliphatic molecules (Helms et al., 2008; Osburn et al., 2011).…”

Reviews and syntheses: VOC emissions from soil cover in boreal and temperate natural ecosystems of the Northern Hemisphere

“…However, it should be noted that this is not the only process linking deciduous litter and soil biota. When litter decomposes, both labile and more stable forms of dissolved organic matter are formed, significantly affecting the binding and consumption of carbon in the soil (Hensgens et al, 2021); however, the chemical composition of compounds leached from the litter and the very scale of this phenomenon remain unexplored.…”