Nitrogen increases early‐stage and slows late‐stage decomposition across diverse grasslands

Abstract

To evaluate how increased anthropogenic nutrient inputs alter carbon cycling in grasslands, we conducted a litter decomposition study across 20 temperate grasslands on three continents within the Nutrient Network, a globally distributed nutrient enrichment experiment We determined the effects of addition of experimental nitrogen (N), phosphorus (P) and potassium plus micronutrient (Kμ) on decomposition of a common tree leaf litter in a long‐term study (maximum of 7 years; exact deployment period varied across sites). The use of higher order decomposition models allowed us to distinguish between the effects of nutrients on early‐ versus late‐stage decomposition. Across continents, the addition of N (but not other nutrients) accelerated early‐stage decomposition and slowed late‐stage decomposition, increasing the slowly decomposing fraction by 28% and the overall litter mean residence time by 58%. Synthesis. Using a novel, long‐term cross‐site experiment, we found widespread evidence that N enhances the early stages of above‐ground plant litter decomposition across diverse and widespread temperate grassland sites but slows late‐stage decomposition. These findings were corroborated by fitting the data to multiple decomposition models and have implications for N effects on soil organic matter formation. For example, following N enrichment, increased microbial processing of litter substrates early in decomposition could promote the production and transfer of low molecular weight compounds to soils and potentially enhance the stabilization of mineral‐associated organic matter. By contrast, by slowing late‐stage decomposition, N enrichment could promote particulate organic matter (POM) accumulation. Such hypotheses deserve further testing.

Stoichiometric imbalances between soil microorganisms and their resources regulate litter decomposition

“…For instance, an increase in soil N availability can accelerate litter decomposition in N‐poor conditions by alleviating N limitation to decomposer communities (Hou et al., 2021). However, although high litter N content often stimulates decomposition rates at the early stage of decomposition, it does not affect long‐term decomposition rates, or it may even reduce it (Gill et al., 2022). This pattern can be attributed to the diminishing pool of simple carbon compounds and reduced access to energy relative to nutrients, which became prevalent during litter decomposition (Fanin et al., 2016).…”

Relative contribution of photodegradation to litter breakdown in Australian grasslands

“…its chemical and morphological characteristics) is a strong predictor of both the rate and pattern of decomposition (Cornwell et al, 2008;Couteaux et al, 1995;Meentemeyer, 1978;Zhang et al, 2008). High concentrations of nutrients in leaves (such as N and P) increases mass loss from labile molecules in the early stages of decomposition (Gill et al, 2022).…”

“…its chemical and morphological characteristics) is a strong predictor of both the rate and pattern of decomposition (Cornwell et al., 2008; Couteaux et al., 1995; Meentemeyer, 1978; Zhang et al., 2008). High concentrations of nutrients in leaves (such as N and P) increases mass loss from labile molecules in the early stages of decomposition (Gill et al., 2022). Recalcitrant molecules, such as lignin, however, are slow to decompose due to their large and complex structure (Coleman et al., 2004; Ruiz‐Duenas & Martinez, 2009).…”

“…Recalcitrant molecules, such as lignin, however, are slow to decompose due to their large and complex structure (Coleman et al., 2004; Ruiz‐Duenas & Martinez, 2009). Furthermore, whilst N promotes the initial decomposition of labile molecules, it can have an inhibitory effect on subsequent stages of litter decomposition (Couteaux et al., 1995; Gill et al., 2022). These factors lead to rapid early‐stage decomposition and slower late‐stage decomposition and hence, to the negative exponential decay curve exhibited in many decomposition studies (Couteaux et al., 1995; Olson, 1963).…”