Biodiversity loss is a major global concern, impacting ecosystem functioning and services. While the impact of biodiversity on primary productivity is well-studied, the influence of plant diversity on decomposition—a critical process in biogeochemical cycles—remains less understood. Decomposition, the breakdown of organic matter, plays a central role in carbon and nutrient cycling, impacting climate feedbacks. This study addresses this knowledge gap by conducting a global meta-analysis to quantify the effects of plant litter diversity on decomposition rates. The after-life effects of plant diversity, referring to the impact of plant species composition on decomposition after plant death, are of particular interest due to their potential influence on long-term ecosystem processes and global change. Understanding these effects is vital for accurate predictions of future biogeochemical cycles and climate change, as altered plant diversity can result from human influences such as habitat simplification and climate change itself. Previous studies have investigated the mechanisms underlying this relationship (nutrient transfer, altered decomposer activity, and positive feedback of decomposers), but a global synthesis is needed to assess the overall impact and magnitude of plant litter diversity on decomposition across various biomes and climate regions.

Existing research indicates a link between plant diversity and ecosystem functioning, with a particular focus on plant diversity's impact on primary productivity and decomposition. However, a comprehensive synthesis of studies examining the relationship between plant litter diversity and decomposition rates has been lacking, limiting confidence in the ability to accurately assess the after-life effects of plant diversity on biogeochemical cycles and climate feedbacks. Several studies have explored the possible mechanisms driving the observed relationships, such as nutrient transfer between different litter species, altered decomposer activity due to litter traits, and positive feedback among decomposers. While these mechanistic studies provide valuable insights, a broader, quantitative synthesis is necessary to assess the overall direction and magnitude of the effects across different biomes and climatic zones.

This study conducted a global-scale meta-analysis of the effects of plant litter diversity on decomposition rates. Data were compiled from 151 studies, including in situ and ex situ litter-bag experiments. The meta-analysis focused on two main measures of decomposition rate: mass loss and the decomposition rate constant, k. A total of 6535 comparisons (mass loss) and 1423 comparisons (rate constant k) were included across various biomes and climatic zones. A multilevel random effects meta-analysis was employed to account for differences among studies and treatments and handle potential non-independence of data points. The analysis investigated the effects of litter diversity across different ecosystem types, climatic regions, and litter substrates. To assess the climate-equivalency of the diversity effects, the study utilized a dataset from a full reciprocal litter transplant experiment to standardize the climate-decomposition relationship. This standardization removed the confounding influences of decomposers and litter traits, allowing for a comparison of the magnitude of diversity effects with projected climate change impacts on decomposition. The CMIP5 RCP 2.6 and 8.5 scenarios were used to project future climate change impacts on decomposition rates by the 2070s. The study used the R software and several packages including 'tidyverse', 'metafor', 'lmerTest', 'effects', 'maptools', 'sf', and 'raster' for data analysis and visualization.

The meta-analysis revealed a significant positive effect of plant litter diversity on decomposition rates across all studies (p < 0.0001 for mass loss and p < 0.01 for rate constant k). This positive effect was consistent across different litter types (leaf litter showed similar results), with significant positive effects observed for most biomes except streams. The analysis identified biome-specific differences in the magnitude of the effects, with stronger positive effects observed in colder forest biomes. The comparison between diversity and climate change impacts on decomposition showed that the increase in decomposition rate due to plant litter diversification (34.7% in forests) is comparable in magnitude to the projected increases due to climate change (13.6% and 26.4% based on RCP 2.6 and 8.5, respectively) in forest biomes. This suggests that the after-life effects of plant diversity are substantial and comparable to the expected impacts of climate change on decomposition.

The findings confirm that plant diversity significantly enhances decomposition rates across various ecosystems, with effects comparable to those projected for climate change over the next 50 years. This emphasizes that biodiversity change is a non-negligible driver of global biogeochemical cycles and climate feedbacks. The study's quantification of the effects of plant litter diversity on decomposition helps address the long-standing lack of synthesis in this area and complements previous work focusing on plant diversity's impact on biomass production. While the net effect of biodiversity changes on the global carbon cycle requires further investigation, the substantial influence of plant diversity on decomposition highlights the need to integrate biodiversity considerations into models of ecosystem functioning and global biogeochemical cycles. The biome-specific differences in the effect sizes suggest complex interactions between biodiversity and environmental factors and call for further research disentangling these interactions.

This study provides compelling evidence for the significant and substantial positive effects of plant litter diversity on decomposition rates. The magnitude of these effects is comparable to the projected impacts of climate change. This underscores the crucial role of biodiversity in regulating biogeochemical cycles and climate feedbacks. The findings highlight the need to incorporate biodiversity considerations into models used to project future changes in these cycles, particularly concerning the increasing prevalence of monoculture plantations. Future research should focus on exploring the interactions between plant diversity, decomposer diversity, and environmental factors, as well as investigating the effects of plant diversity in communities with a greater number of species than those included in this meta-analysis.

This study mainly relied on data from monocultures and mixtures of two or three species, limiting the ability to extrapolate the findings to communities with more complex species compositions. The study also recognized the context-dependency of the relationships, with temporal variation and differences across systems potentially influencing the results. The influence of decomposer diversity on the observed relationships was not fully assessed, highlighting the need for further research in this area. The methodology for comparing the effects of diversity and climate change relied on certain assumptions about climate-decomposition relationships, and limitations in data availability restricted analysis to specific biomes and litter types.