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Biodiversity mediates the effects of stressors but not nutrients on litter decomposition.

ABSTRACT: Understanding the consequences of ongoing biodiversity changes for ecosystems is a pressing challenge. Controlled biodiversity-ecosystem function experiments with random biodiversity loss scenarios have demonstrated that more diverse communities usually provide higher levels of ecosystem functioning. However, it is not clear if these results predict the ecosystem consequences of environmental changes that cause non-random alterations in biodiversity and community composition. We synthesized 69 independent studies reporting 660 observations of the impacts of two pervasive drivers of global change (chemical stressors and nutrient enrichment) on animal and microbial decomposer diversity and litter decomposition. Using meta-analysis and structural equation modeling, we show that declines in decomposer diversity and abundance explain reduced litter decomposition in response to stressors but not to nutrients. While chemical stressors generally reduced biodiversity and ecosystem functioning, detrimental effects of nutrients occurred only at high levels of nutrient inputs. Thus, more intense environmental change does not always result in stronger responses, illustrating the complexity of ecosystem consequences of biodiversity change. Overall, these findings provide strong evidence that the consequences of observed biodiversity change for ecosystems depend on the kind of environmental change, and are especially significant when human activities decrease biodiversity.

SUBMITTER: Beaumelle L

PROVIDER: S-EPMC7402682 | biostudies-literature | 2020 Jun

REPOSITORIES: biostudies-literature

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Biodiversity mediates the effects of stressors but not nutrients on litter decomposition.

Beaumelle Léa L De Laender Frederik F Eisenhauer Nico N

eLife 20200626

Understanding the consequences of ongoing biodiversity changes for ecosystems is a pressing challenge. Controlled biodiversity-ecosystem function experiments with random biodiversity loss scenarios have demonstrated that more diverse communities usually provide higher levels of ecosystem functioning. However, it is not clear if these results predict the ecosystem consequences of environmental changes that cause non-random alterations in biodiversity and community composition. We synthesized 69 i ...[more]

PMID: 32589139

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Project description:Global contamination of streams by a large variety of compounds, such as nutrients and pesticides, may exert a high pressure on aquatic organisms, including microbial communities and their activity of organic matter decomposition. In this study, we assessed the potential interaction between nutrients and a fungicide and herbicide [tebuconazole (TBZ) and S-metolachlor (S-Met), respectively] at realistic environmental concentrations on the structure (biomass, diversity) and decomposition activity of fungal and bacterial communities (leaf decay rates, extracellular enzymatic activities) associated with Alnus glutinosa (Alnus) leaves. A 40-day microcosm experiment was used to combine two nutrient conditions (mesotrophic and eutrophic) with four pesticide treatments at a nominal concentrations of 15 ?g L-1 (control, TBZ and S-Met, alone or mixed) following a 2 × 4 full factorial design. We also investigated resulting indirect effects on Gammarus fossarum feeding rates using leaves previously exposed to each of the treatments described above. Results showed interactive effects between nutrients and pesticides, only when nutrient (i.e., nitrogen and phosphorus) concentrations were the highest (eutrophic condition). Specifically, slight decreases in Alnus leaf decomposition rates were observed in channels exposed to TBZ (0.01119 days-1) and S-Met (0.01139 days-1) than in control ones (0.01334 days-1) that can partially be explained by changes in the structure of leaf-associated microbial communities. However, exposition to both TBZ and S-Met in mixture (MIX) led to comparable decay rates to those exposed to the pesticides alone (0.01048 days-1), suggesting no interaction between these two compounds on microbial decomposition. Moreover, stimulation in ligninolytic activities (laccase and phenol oxidase) was observed in presence of the fungicide, possibly highlighting detoxification mechanisms employed by microbes. Such stimulation was not observed for laccase activity exposed to the MIX, suggesting antagonistic interaction of these two compounds on the ability of microbial communities to cope with stress by xenobiotics. Besides, no effects of the treatments were observed on leaf palatability for macroinvertebrates. Overall, the present study highlights that complex interactions between nutrients and xenobiotics in streams and resulting from global change can negatively affect microbial communities associated with leaf litter, although effects on higher trophic-level organisms remains unclear.

Project description:Exploring how interactions between species evenness and dominant species identity affect litter decomposition processes is vital to understanding the relationship between biodiversity and ecosystem functioning in the context of global changes. We carried out a 127-day litter decomposition experiment under controlled conditions, with interactions of four species evenness types (high, medium, low and single species) and three dominant species identity (Leymus chinensis, Serratula centauroides, Artemisia capillaris). After collecting the remaining litter, we estimated how evenness and dominant species identity affected litter mass loss rate, carbon (C) loss rate, nitrogen (N) loss rate and remaining litter C/N directly or indirectly, and assessed relative mixture effects (RMEs) on litter mass loss. The main results are shown as follows. (1) By generalized linear models, litter mass loss rate was significantly affected by evenness after 69-day decomposition; N loss rate was affected by dominant species identity after 69-day decomposition, with treatment dominated by Serratula centauroides being at least 9.26% higher than that dominated by any of other species; and remaining litter C/N was affected by the interactions between evenness and dominant species identity after 30-, 69- and 127-day decomposition. (2) Twenty-three out of 27 RMEs were additive, and dominant species identity showed a significant effect on RMEs after 127-day decomposition. (3) By confirmatory path analyses, litter mass loss rate was affected by dominant species identity directly after 127-day decomposition, and by both species evenness and dominant species identity indirectly which was mediated by initial litter functional dispersion (FDis) after 30- and 69-day decomposition; remaining litter C/N was affected by evenness indirectly which was mediated by initial litter FDis after 127-day decomposition. These findings highlight the importance of evenness and dominant species identity on litter decomposition. The study provides insights into communities during retrogressive successions in semi-arid grasslands in the context of global changes.

Project description:High severity wildfire events are a feature of forests globally and are likely to be more prevalent with climate change. As a disturbance process, fire has the potential to change important ecological functions, such as decomposition, through its impact on biodiversity. Despite the recognised importance of decomposition in terms of fuel loads and energy flow, little is known about the post-fire effects of fire severity on decomposition by litter-dwelling macroinvertebrate detritivores. We tested the hypotheses that: 1) increasing fire severity is associated with decreased rates of leaf litter decomposition by macroinvertebrate detritivores; and 2) the abundance and biomass of macroinvertebrate detritivores decreases with increasing fire severity, while body size increases. We used a litterbag experiment at long-unburnt, ground-burnt and crown-burnt sites (n = 7 for all treatments) to test the effect of fire severity on: a) macroinvertebrate-driven break-down of litter fuel loads; and b) the size and abundance of macroinvertebrate detritivores three years after fire. Microhabitat conditions differed among fire severity classes. Macroinvertebrate exclusion reduced litter decomposition by 34.7%. Macroinvertebrate detritivores were larger and less abundant following higher severity fires, possibly as a result of fire-induced changes in habitat structure. Opposing effects of fire severity on macroinvertebrate abundance and body size resulted in both similar detritivore biomass and, most interestingly, no differences in leaf litter decomposition under different fire severities. This suggests that the diversity of macroinvertebrates enhances functional resilience of litter decomposition to fire and that litter-breakdown is not inhibited within three years following a high severity fire in this forest type and where recolonisation sources are readily available. We found no support for the hypothesis that high severity fires reduce litter decomposition and therefore increase the likelihood of future fires.

Dataset Information

Biodiversity mediates the effects of stressors but not nutrients on litter decomposition.

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Biodiversity mediates the effects of stressors but not nutrients on litter decomposition.

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