Nannan An

Climatic extremes and wildfire can disrupt soil communities, but the consistency of abundance responses across disturbance types remains unclear. We synthesized 425 abundance contrasts from 30 publications using sample size weights normalized within publications. Multilevel models accounted for clustering by publication. The overall mean reduction was 33.6%, with the clearest statistical support for wildfire. Hydroclimatic and storm estimates were uncertain, and thermal studies were summarized descriptively. Restricting the synthesis to 25 publications with suitable terrestrial exposure and reference comparisons yielded a 41.6% reduction across 322 observations. The average response remained negative under stricter event criteria and across alternative weights, taxonomic subsets and sampling methods. Direct tests detected no differences between body-size classes or between forests and grasslands within wildfire. Temporal analyses did not establish a common recovery pattern. Analyses using reported variances indicated high heterogeneity and a prediction interval spanning zero. Soil fauna abundance therefore declined on average, particularly following wildfire, but this response cannot be assumed across all disturbances or locations. Including soil fauna abundance in disturbance monitoring would improve assessment of belowground impacts that aboveground damage alone may not reveal.

Environmental change can alter aboveground and belowground plant inputs, with consequences for soil carbon (C) and nitrogen (N) cycling and their coupling. However, how soil C and N respond differently to root and litter removal, and which factors regulate these responses, remain unclear. Here, we conducted a meta-analysis to quantify changes in soil C and N following root and aboveground litter (hereafter, litter) removal and to identify the factors associated with these changes. We found that (1) litter removal significantly decreased soil organic C (SOC), dissolved organic C, total N, microbial biomass N, ammonium N concentrations and nitrous oxide emissions by 11%–30%, whereas root removal increased nitrate N concentration by 88%; (2) the response ratios of microbial biomass C and N were not correlated under either root or litter removal, whereas those of total C and N concentrations were positively correlated; (3) the effects of root and litter removal on soil C and N varied with season and soil depth, with the strongest responses occurring in autumn and winter and in the surface soil layer (0–10 cm); and (4) these responses were moderated primarily by leaf type and, to a lesser extent, by ecosystem type, elevation, mean annual precipitation, soil properties and experimental duration. Overall, our results clarify how altered plant inputs affect soil C and N pools and identify the conditions under which these effects are strongest, thereby informing predictions of C and N cycling under global change.

Forest canopy opening can significantly affect understory environment and thus further influence the communities of soil biota, but this has not been well quantified in the literature. Here, using meta-analysis method, we evaluated the effects of forest canopy opening on soil fauna density and diversity as well as microbial biomass using 4056 paired observations. We found that (1) as a whole, forest canopy opening showed positive effects on soil fauna communities, significantly increasing the density of total soil fauna by 70.5%, and the total richness, Margalef index, and fungi abundance by 33.1, 30.0, and 64.1%, respectively; (2) canopy opening significantly decreased the Pielou index, bacteria abundance, and soil microbial biomass phosphorus concentration by 16.0, 20.9, and 21.0%, respectively, but did not affect microbial biomass carbon or nitrogen concentration; and (3) forest canopy opening effects on soil biota were regulated by latitude, elevation, climate, canopy opening size, and soil pH, with canopy opening size being the most important factor. Overall, our results demonstrate significantly positive impacts of forest canopy opening on soil fauna and fungi abundance but negative influences on other microbes, which will help us to better understand and predict the responses of soil biota to environmental changes and provide theoretical references for forest management and biodiversity conservation under future environmental change scenarios.

Nitrogen (N) deposition strongly affects litter decomposition and nutrient release, thereby reshaping carbon cycling in terrestrial ecosystems. Although most studies have focused on above‐ground litter, the effects of N addition on fine root decomposition and their underlying drivers, particularly across different root characteristics, remain poorly understood. We synthesized a meta‐analysis of 144 observations from 30 studies to quantify the response of fine root decomposition rates to N addition and to identify the key factors that regulate these responses across root characteristics. On average, N addition reduced fine root decomposition rates and mass loss by 8.52% and 6.24%, respectively. Negative responses to N addition were most pronounced in roots ≤2 mm in diameter and in first‐ and second‐order roots. Soil microbial biomass N and clay content were the dominant drivers of these responses in roots ≤2 mm. Within different root characteristics, soil microbial biomass N and soil N content were the most important factors regulating the response of decomposition rates to N addition for roots ≤1 mm, while N addition amount was the key determinant for third‐ to fifth‐order roots. These results suggest that the controls on fine root decomposition under N addition vary with root characteristics. This highlights the need to incorporate root variability into ecosystem models to improve predictions of below‐ground carbon cycling under future climate change. Read the free Plain Language Summary for this article on the Journal blog.

Headwater streams serve as a crucial link between forest and downstream aquatic ecosystems and also act as crucial agents in carbon (C) and nutrient storage and flux. These aquatic systems play a pivotal role in regulating biogeochemical cycles. Plant litter is an important contributor of nutrients to headwater streams, having significant impacts on downstream ecosystems. However, current research predominantly focuses on the dynamics of plant litter C and nutrients such as nitrogen and phosphorus, and we know little about those of nutrients such as sodium (Na). In this study, we conducted a comprehensive evaluation of the annual dynamics of plant litter Na storage within a subtropical headwater stream. This study took place over a period of one year, from March 2021 to February 2022. Our results showed that (1) the average annual concentration and storage of litter Na was 538.6 mg/kg and 2957.6 mg/m², respectively, and litter Na storage exhibited a declining trend from stream source to mouth, while demonstrating significantly higher values during the rainy season compared to the dry season; (2) plant litter type had significant impacts on Na concentration and storage, with leaf, twig, and fine woody debris accounting for the majority of litter Na storage; and (3) hydrological (precipitation, discharge) and physicochemical (water temperature, flow velocity, pH, dissolved oxygen, alkalinity) factors jointly affected Na storage patterns. Overall, the results of this study clearly reveal the dynamic characteristics of Na storage in plant litter in a subtropical forest headwater stream, which contributes to a more comprehensive understanding of the role of headwater streams in nutrient cycling and the dynamic changes of nutrients along with hydrological processes. This research will enhance our predictive understanding of nutrient cycling at the watershed scale.

Aim: Seed mass is a key reproductive trait and is closely related to seed dispersal, germination, seedling growth and competition capability. Characterising the geographical pattern and the primary factors of seed mass variation is crucial for understanding plant reproductive strategy under heterogeneous environments. However, how the environment, phylogeny and life history traits simultaneously affect the variation in seed mass in China and their differences across climate regions remains unclear.Location: China.Major Taxa Studied: Angiosperm species.Methods: We compiled a database on seed mass comprising 4569 observations that belong to 2064 angiosperms from 1152 sampling sites in China. A phylogenetic linear mixed model was used to disentangle the relative contributions of environment, phylogeny and life history traits (i.e. plant growth form, fruit type and dispersal mode) to seed mass variation. This analysis was conducted on a national scale and four climate regions, including tropical, subtropical, temperate and plateau regions.Results: Seed mass was significantly associated with annual climatic averages and climate variability and seasonality variables. Soil pH was strongly related to seed mass, while soil nutrients were not. Environment, phylogeny and life history traits together explained 75.3%–86.6% of the total variation in seed mass in China and four climate regions. Life history traits and phylogeny were the most important factors of seed mass variation in China and most climate regions (14.2%–30.1% and 8.0%–19.7%, respectively) except for the tropical region. In the tropical region, environment was the strongest driver of seed mass variation (52.6%).Main Conclusion: Our study emphasised the differences in environmental and ecological effects on seed mass under heterogeneous climatic contexts and provided a reference for continued research on the complex interactions between plant reproductive strategy, evolutionary process and the environment.

The initial concentration of litter nutrient not only affects the following decomposition process but also determines the quantities of nutrients returned to the soil. The aim of this study is to assess the global patterns and driving factors of three macronutrients, namely potassium (K), calcium (Ca) and magnesium (Mg), in freshly fallen litter. By synthesizing 5861 data points extracted from 584 publications, we quantitatively evaluated the concentrations of litter K, Ca and Mg in different litter types, life forms, taxonomic divisions and mycorrhizal associations. Also, using the machine learning method, we predicted their global patterns in forests, grasslands and shrublands. We found that (1) mean K, Ca and Mg concentrations ranged from 2.63 to 6.23, 1.05 to 11.50 and 0.20 to 2.74 g/kg, respectively, across different litter types; (2) the initial nutrients of the litter were significantly affected by plant functional types (e.g. life form, taxonomic division and mycorrhizal association), climate (e.g. isothermality, mean diurnal range, annual evapotranspiration and precipitation seasonality) and soil properties (e.g. pH, exchangeable Ca concentration and water content), with a higher litter K concentration of herbaceous plants, higher K, Ca and Mg concentrations from angiosperms and higher K and Mg concentrations from plants associated with arbuscular mycorrhiza (AM) fungi; and (3) the predicted leaf litter K, Ca and Mg concentrations were lower in high‐latitude regions compared with those in low‐ and/or mid‐latitude regions. Our study provides a globally comprehensive analysis on the patterns and driving factors of three important macronutrients in freshly fallen litter, contributing to a better understanding of their role in the decomposition process of litter, as well as the associated biogeochemical cycles under the future climate change scenario. Read the free Plain Language Summary for this article on the Journal blog.