Contrasting geochemical and fungal controls on decomposition of lignin and soil carbon at continental scale

Abstract

Lignin is an abundant and complex plant polymer that may limit litter decomposition, yet lignin is sometimes a minor constituent of soil organic carbon (SOC). Accounting for geographic diversity in soil characteristics might reconcile this apparent contradiction. We tracked decomposition of a lignin/litter mixture across North American mineral soils using lab and field incubations. Cumulative lignin decomposition varied 18-fold among soils and was strongly correlated with bulk litter decomposition, but not SOC decomposition. Legacy climate predicted decomposition even in the lab. Impacts of nitrogen availability were minor compared with geochemical and microbial properties, which had contradictory relationships with lignin and SOC decomposition. Lignin decomposition increased with some metals and fungi, whereas SOC decomposition decreased with all metals and was weakly related with fungi. Soil properties differentially impact decomposition of lignin and litter vs. SOC across broad geographic scales, linking short-term decomposition to differences in organic matter among ecosystems.

Modeling Interactive Effects of Manganese Bioavailability, Nitrogen Deposition, and Warming on Soil Carbon Storage

“…Furthermore, stimulatory effects of Mn on litter decomposition may be absent or difficult to identify across ecosystems owing to factors other than redox and pH that limit Mn bioavailability and/or influence litter decomposition (Kranabetter et al., 2021; Li et al., 2021; Trum et al., 2011). For example, Mn accelerates transformation of litter and POM C but may not ultimately affect C storage because decomposed C is then retained in more stable pools (Possinger et al., 2022), possibly explaining negative correlations between soil Mn and soil C decomposition (Huang et al., 2023). In addition, soils that are highly weathered may contain crystalline Mn oxides that are poorly soluble, as simulated in this study by varying birnessite dissolution rates, or may become Mn depleted due to leaching of Mn from the soil over time (Kranabetter et al., 2021).…”

“…Furthermore, experimental additions of aqueous Mn 2+ to forest soils stimulate soil respiration and CO 2 release (Li et al., 2021; Trum et al., 2011, 2015). These effects may be attributed to Mn‐promoted lignin decomposition that increases lignin and thus litter C loss over long timescales (Huang et al., 2023; Yi et al., 2023). However, the ecosystem‐scale implications of these complex biogeochemical interactions remain to be explored.…”

Resolving the influence of lignin on soil organic matter decomposition with mechanistic models and continental‐scale data

“…Soil samples spanned a broad range of biogeochemical characteristics (Table S1) and land cover types (forest, grassland/shrubland, and wetland). In the laboratory incubation dataset, the decomposition of C 4 grass litter, 13 C‐labeled lignin, and soil C was monitored over time (Figure 2) by measuring the stable C isotope ratio (δ 13 C) values of CO 2 from replicates of each soil that received substrates with different δ 13 C values; these empirical data are described in detail in our published paper (Huang et al, 2023). Three separate treatments were implemented for each soil sample: including (1) incubating the soil alone; (2) the soil amended with C 4 grass ( Androgopon gerardi ) litter + natural abundance synthetic lignin; and (3) the soil amended with C 4 grass litter + 13 C‐labeled lignin at the C β position of the propyl sidechain.…”

“…In this data-model fusion work, we analyzed a published laboratory incubation dataset (Huang et al, 2022) to understand lignin decomposition trajectories and their relationships with litter and soil decomposition in soils sampled from across the United States. We first explored what biogeochemical indicators predicted the grouping of lignin decomposition trajectories (i.e., no-peak and lagged-peak groups).…”

“…In addition to underrepresented mechanisms, testing and validating lignin's roles in C decomposition models remains challenging due to a lack of systematic observation datasets that measure lignin decomposition in soils with diverse geochemical and microbial properties. In this study, a process‐based decomposition model was confronted with a recently published laboratory incubation data set (Huang et al, 2022) to address these challenges.…”