Nutrient and stoichiometry dynamics of decomposing litter in stream ecosystems: A global synthesis

Abstract

Decomposing organic matter forms a substantial resource base, fueling the biogeochemical function and secondary production of most aquatic ecosystems. However, detrital N (nitrogen) and P (phosphorus) dynamics remain relatively unexplored in aquatic ecosystems relative to terrestrial ecosystems, despite fundamentally linking microbial processes to ecosystem function across broad spatial scales. We synthesized 217 published time series of detrital carbon (C), N, P, and their stoichiometric ratios (C:N, C:P, N:P) from stream ecosystems to analyze the temporal nutrient dynamics of decomposing litter using generalized additive models. Model results indicated that detritus was a net source of N (irrespective of inorganic or organic form) to the environment, regardless of initial N content. In contrast, P sink/source dynamics were more strongly influenced by the initial P content, in which P‐poor litters were sinks for nutrients until these shifted to net P mineralization after ~40% mass loss. However, large variations surrounded both the N and P predictions, suggesting the importance of nonmicrobial factors such as fragmentation by invertebrates. Detrital C:N ratios converged and became more similar toward the end of the decomposition, suggesting predictable microbial functional effects throughout detrital ontogeny. C:P and N:P ratios also converged to some degree, but these model predictions were less robust than for C:N, due in part to the lower number of published detrital C:P time series. The explorations of environmental covariate effects were frequently limited by a few coincident covariate measurements across studies, but temperature, N availability, and P tended to accelerate the existing ontogenetic patterns in C:N. Our analysis helps to unite organic matter decomposition across aquatic–terrestrial boundaries by describing the basic patterns of elemental flows catalyzed by decomposition in streams, and points to a research agenda with which to continue addressing gaps in our knowledge of detrital nutrient dynamics across ecosystems.

Reciprocal stream–riparian fluxes: effects of distinct exposure patterns on litter decomposition

“…Notwithstanding, this effect of movement sequence on mass loss only occurred in coarse mesh bags. A short (i.e., 2 weeks) pre-conditioning terrestrial period followed by stream exposure contributed to a higher fungal biomass; although this is usually determinant of high leaf consumers' activity (Canhoto and Graça 2008), in our case it was likely not enough to surpass or compensate oak's inherent low leaf quality (e.g., thick cuticle, high lignin content, and leaf toughness) (Gulis et al 2006;Jabiol and Chauvet 2012;Robbins et al 2023), resulting in lower detritivore consumption. Likely, the potentially delayed leaching and microbial conditioning that occurred during the terrestrial pre-conditioning period may have delayed and restricted the optimal time window for aquatic detritivore activity.…”

Leaves stimulate aquatic phosphorus uptake by dark‐grown but not by light‐grown microbial communities in sediments: A laboratory study

“…As leaf decomposition changes with time, the decomposition state of leaves controls their impact on the uptake of externally supplied nutrient (Cheever et al, 2012;Ferreira et al, 2015;Robbins et al, 2023;Webster et al, 2009). showing a shift from net nutrient uptake at an early state of leaf decomposition to net release at a later stage.…”

“…Oviedo-Vargas et al (2013), for example, found no stimulation of P uptake through acetate additions in streams, probably due to autotrophic competition for the P and/or the microbial use of P and OC already stored in the sediments. Besides, P adsorption may dominate P retention in streams (Griffiths & Johnson, 2018;Robbins et al, 2023;Stutter, Graeber, & Weigelhofer, 2020) but this process is mostly independent of the OC availability (Li et al, 2020).…”

“…Leaves amount to c. 41%-98% of total terrestrial POC inputs to streams and deliver OC of high complexity to the stream biota (Zhang et al, 2019). Leaves provide habitat for the aquatic microbiome (Marks, 2019;O'Brien et al, 2017;Zhang et al, 2019) and can also act as adsorption sites for P (Mehring et al, 2015;Robbins et al, 2023). Numerous studies have shown a strong coupling between nutrient availability and leaf degradation (Bastias et al, 2018;Danger et al, 2021;Marks, 2019) but the reverse effects of POC availability on the microbial nutrient uptake have rarely been investigated so far (but see, e.g., O'Brien et al, 2017;Gibson & O'Reilly, 2012).…”

“…Robbins et al (2023) modelled nutrient dynamics of decomposing litter from data of published studies. They found that P dynamics were strongly affected by the initial P content.…”