Litter Quality Is a Stronger Driver than Temperature of Early Microbial Decomposition in Oligotrophic Streams: a Microcosm Study

Abstract

Litter decomposition is an ecological process of key importance for forest headwater stream functioning, with repercussions for the global carbon cycle. The process is directly and indirectly mediated by microbial decomposers, mostly aquatic hyphomycetes, and influenced by environmental and biological factors such as water temperature and litter quality. These two factors are forecasted to change globally within the next few decades, in ways that may have contrasting effects on microbial-induced litter decomposition: while warming is expected to enhance microbial performance, the reduction in litter quality due to increased atmospheric carbon dioxide and community composition alteration may have the opposite outcome. We explored this issue through a microcosm experiment focused on early microbial-mediated litter decomposition under stream oligotrophic conditions, by simultaneously manipulating water temperature (10 °C and 15 °C) and litter quality (12 broadleaf plant species classified into 4 categories based on initial concentrations of nitrogen and tannins). We assessed potential changes in microbial-mediated litter decomposition and the performance of fungal decomposers (i.e., microbial respiration, biomass accrual, and sporulation rate) and species richness. We found stronger effects of litter quality, which enhanced the performance of microbial decomposers and decomposition rates, than temperature, which barely influenced any of the studied variables. Our results suggest that poorer litter quality associated with global change will have a major repercussion on stream ecosystem functioning.

Functional consequences of alder and oak loss in stream ecosystems

“…Previous studies allow the elaboration of likely predictions for current species loss outcomes, as has been observed in this study, where results of decomposition and aquatic hyphomycete assemblages were consistent with the hypotheses predicted from more general studies regarding random species loss and effects of specific leaf traits (Ferreira et al, 2012;Kominoski et al, 2007;Larrañaga et al, 2020;López-Rojo et al, 2018;McArthur et al, 1994;Pérez, Ferreira, et al, 2021), despite doing so in the form of non-significant trends. However, in the cases when the loss of more than one species is considered, predictions based on more general research are more difficult, due to the loss of different traits (López-Rojo et al, 2018).…”

“…This matches previous work in our study area (Chauvet et al, 1997; Mendoza–Lera et al, 2012; Pérez et al, 2012), where F. curvula is an early coloniser of decomposing litter (Treton et al, 2004). Despite the absence of differences with the control, sporulation rate was lower for the scenario with alder loss than for scenarios where oak was reduced or lost, suggesting a limitation to sporulation (or a later sporulation peak) in the former scenario due to lower nutrient availability and/or higher presence of lignin and tannins (Ferreira et al, 2012; Kominoski et al, 2007; Pérez, Ferreira, et al, 2021).…”

“…These NDEs were negligible at the first stages of the decomposition, suggesting that microbial responses are observed in longer studies, and thus they are not found in most short‐term microcosm experiments. However, under usual conditions, a great portion of leaf litter inputs only undergoes initial decomposition in the stream benthos before being transported downstream, incorporated into the sediments during periods of high sediment movement (e.g., spates), or emerged if the stream dries out (e.g., intermittent streams) (Graça et al, 2015; Tonin et al, 2021), making the initial litter decomposition phases the most relevant to assess (Pérez, Ferreira, et al, 2021).…”

“…These NDEs were negligible at the first stages of the decomposition, suggesting that microbial responses are observed in longer studies, and thus they are not found in most shortterm microcosm experiments. However, under usual conditions, a great portion of leaf litter inputs only undergoes initial decomposition in the stream benthos before being transported downstream, incorporated into the sediments during periods of high sediment movement (e.g., spates), or emerged if the stream dries out (e.g., intermittent streams) (Graça et al, 2015;Tonin et al, 2021), making the initial litter decomposition phases the most relevant to assess (Pérez, Ferreira, et al, 2021). Sericostoma growth was highly variable within treatments and did not differ between the control and the scenarios, which contradicted our hypothesis but agreed with other studies in which detritivore growth did not respond to treatments of litter diversity (Lopez-Rojo et al, 2020;López-Rojo et al, 2019;Tonin et al, 2017) or quality (Larrañaga et al, 2020).…”

Effects of Pesticides on the Survival of Shredder Nectopsyche sp. (Trichoptera) and Leaf Decomposition Rates in Tropical Andes: A Microcosm Approach

“…It is important to denote other factors that intervene in the components of decomposition. The forest quality is highlighted as a factor that determines the importance of decomposers by the K g /K f quotient, and in Andean rivers with high forest quality, the shredders are determined to be important to the decomposition rates [48], while the importance of microorganisms increases in impacted rivers [49,50]. This is one of the limitations of our study.…”