Zilong Ma

Pathogens and herbivores are key to diversity-productivity relationships. However, the extent to which plant diversity maintains higher productivity by reducing biomass loss from pathogens and herbivores remains unclear at the global scale. Based on a meta-analysis of 2315 observations from 316 studies, we show that, compared to monocultures, plant mixtures on average reduce pathogens abundance and damage to plants by 30.1% and 31.7% and those of invertebrate herbivores by 21.6% and 25.1%, while increasing plant productivity by 40.1% and 35.7%, respectively. Mixture effects on specialist pathogens and invertebrate herbivores become more negative with increasing plant taxonomic, functional, and phylogenetic diversity in mixtures, while those on generalist pathogens and invertebrate herbivores show no significant relationships with any diversity metrics. Mixture effects on pathogens decrease with stand age but those on invertebrate herbivores shift from negative to positive with stand age. Mixture effects on pathogens and invertebrate herbivores are negatively associated with those on productivity. Our findings highlight that conserving plant diversity could reduce biotic damage to plants and enhance global primary productivity.

As key members of the terrestrial food webs and vital contributors to wood decomposition, beetles play essential roles in ecosystem services but are experiencing widespread declines under climate change. While protecting and restoring forests with high tree species diversity is widely acknowledged as a nature‐based solution for climate change mitigation, it remains uncertain whether it helps maintain the stability of higher trophic communities (e.g. beetles) under climate change. Here, we used the comprehensive forest and ground‐dwelling beetle inventory dataset spanning the entire latitudinal range of the Japanese archipelago, monitored from 2004 to 2018, to investigate how tree species diversity affects the temporal stability of beetle biomass. We found that tree species diversity increased beetle biomass and its temporal stability. Specifically, higher tree diversity supported greater beetle and trophic diversity, which enhanced the asynchronous population dynamics across species and trophic levels (i.e. species and trophic asynchrony). Meanwhile, higher beetle and trophic diversity promoted temporal stability at the species level (i.e. species stability). Higher asynchrony and species stability jointly increased temporal stability within beetle communities. Our results underscore the potential of conservation efforts targeting forest diversity to uphold the ecosystem functions of higher trophic level communities (e.g. beetles) under climate change.

Understanding spatiotemporal variation in individual tree growth–functional traits relationships (GTRs) is crucial to predicting forest growth responses to changing environments, aiding in long‐term forest planning and sustainability. Although weak GTRs have been frequently observed within individual forest site or across sites of similar climates and development stages, GTRs at large spatial scales remain uncertain. We hypothesize that GTRs at large scales are regulated by stand development and regional climate through their effects on competition intensity and tree mortality rates. We used forest inventory data in the United States (9828 plots and 228,981 trees) to investigate how stand age and regional climate (temperature and climate moisture index) regulate GTRs. We found an overall positive relationship between relative tree growth rate and stem traits associated with acquisitive strategies (greater height and lower wood density). However, leaf traits associated with acquisitive strategies (higher specific leaf area, leaf nitrogen and phosphorus content) exhibited divergent effects, promoting growth in angiosperms but reducing growth in gymnosperms. Importantly, GTRs weakened with stand age but strengthened with increasing mean annual temperature. Structural equation modelling showed that stand age indirectly weakened GTRs by increasing stand basal area and tree mortality. Synthesis . Our findings suggest that current efforts focusing on planting acquisitive tree species for rapid carbon sequestration may become less effective as forests mature, especially in conservation forests aimed at providing long‐term ecosystem services. Therefore, mixing conservative trees with longer growth cycles alongside acquisitive species could be a forest management strategy to enhance carbon sequestration over the long term.

Whether and how the responses of above‐ (AGB) and below‐ground biomass (BGB) and above‐ground net primary production (ANPP) to global changes are linked to plant functional traits is unclear. We conducted a global meta‐analysis based on 2561 observations from 318 manipulative studies (primarily forest, grassland and cropland monocultures) to examine the effect of plant functional traits (i.e. morphological and chemical traits, mycorrhizal association type and symbiotic nitrogen (N) fixation) of dominant species on the responses of plant biomass production to global change drivers, that is, elevated CO ₂ (eCO ₂ ), elevated nutrient (eNutrient), elevated water (eWater), warming and drought. Across all terrestrial ecosystems studied, eCO ₂ , eNutrient and eWater increased, while drought reduced biomass production. Warming had no overall effect on any of the biomass production metrics. Importantly, the positive effects of eNutrient on BGB were more pronounced for communities dominated by ‘fast’ species (with high specific leaf area and leaf N content). Plant communities dominated by plants with low resource uptake rates by roots exhibited stronger effects of eCO ₂ on ANPP and weaker effects of eNutrient on AGB, BGB and ANPP. In communities dominated by arbuscular mycorrhizal fungi‐associated plants, eNutrient increased AGB and ANPP, and drought reduced AGB. In contrast, eNutrient and drought increased BGB in communities dominated by ectomycorrhizal fungi‐associated plants. eCO ₂ increased ANPP in communities dominated by non‐N‐fixing species but not in communities dominated by N‐fixing species. Synthesis . Accounting for functional traits of dominant plants improves the predictability of ecosystem responses to global change, and can guide ecological management practices to safeguard key ecosystem functions in a rapidly changing world.

Under biogeochemical niche (BN) theory, plant allocation of elements to organs to maintain fundamental biological processes varies with species, leading to the formation of species‐specific BNs. However, empirical support for the BN theory is largely restricted to plant leaf elemental composition and stoichiometry, with a lack of clarity about the contribution of fine root element content. Here, we analysed fine root concentrations and stoichiometry of 9 elements including carbon (C), nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), iron (Fe), aluminium (Al) and manganese (Mn) in 137 tree species of a subtropical forest to quantify BN and test the theoretical framework of the BN hypothesis. Our study showed phylogenetic signals of fine root elemental composition and stoichiometry. Fine root elemental composition of the 21 most abundant co‐existing species tends to be unique and primarily driven by root N content, as indicated by canonical discriminant analysis. Legacy effects (phylogeny and species) explained 23.3%–70.7% of the variation across the different variables used to characterize fine root elemental composition, stoichiometry and BNs, whereas combined effects of soil property, mycorrhizal association type and topography factors explained 3.9%–17.7%. Synthesis: These results indicate that phylogenetic and taxonomic distance (calculated as distance metrics) represent a proxy for species‐specific evolution and achievement of optimal function linked to bio‐element use. Thus, our study provides new empirical evidence in support of the BN hypothesis, based on plant fine root elemental composition and stoichiometry, and improves our mechanistic understanding of species coexistence dynamics.

There is compelling experimental evidence and theoretical predictions that temporal stability of productivity, i.e., the summation of aboveground biomass growth of surviving and recruitment trees, increases with succession. However, the temporal change in productivity stability in natural forests, which may undergo functional diversity loss during canopy transition, remains unclear. Here, we use the forest inventory dataset across the eastern United States to explore how the temporal stability of forest productivity at multi-spatial scales changes with stand age during canopy transition. We find that productivity stability decreases with stand age at the local and metacommunity scales. Specifically, consistent declines in local diversity result in less asynchronous productivity dynamics among species over succession, consequently weakening local stability. Meanwhile, increasing mortality and the transition from conservative to acquisitive species with succession weaken species and local stability. Successional increases in species composition dissimilarity among local communities cause more asynchronous productivity dynamics among local communities. However, the decline in local stability surpasses the rise in asynchronous productivity dynamics among local communities, resulting in lower metacommunity stability in old forests. Our results suggest lower productivity stability in old-growth forests and highlight the urgency of protecting diversity at multiple spatial scales to maintain productivity stability.

Interactions between plants and soil microorganisms in the rhizosphere are vital for maintaining the nutrient cycle and stability of terrestrial ecosystems. Nitrogen, closely related to carbon (C) cycling and ecosystem productivity, undergoes transformation by soil microorganisms into forms that can be assimilated by plants. However, the mechanism by which plants impact nitrogen (N) cycling in acid subtropical forest soil by governing the rhizosphere microbial community remains unclear. This study examined the impact of host phylogeny, root traits, and soil properties on microbial communities and N cycles in the rhizospheres of Fagaceae and Lauraceae, the two dominant families in the subtropical forest of Heishiding Natural Reserve in southern China. Our findings revealed that host phylogeny dominates the variation in the richness and composition of the rhizosphere microbial community. Furthermore, antibacterial exudates from Lauraceae might reduce the stability of microbial network structure and enrich fatty acid biosynthesis function for antimicrobial resistance. Net nitrification rates (NNR) and nitrifying enzyme activities (NEA) of arbuscular mycorrhizae trees of Lauraceae were significantly higher than those of ectomycorrhizae trees of Fagaceae. The positive relationships among NNR, NEA, and root nitrogen content suggest a close correlation between soil nitrification activity and N uptake efficiency by plants. Complete ammonia oxidizer (comammox) dominated the ammonia‐oxidizing communities of these acid soils, followed by ammonia‐oxidizing archaea and ammonia‐oxidizing bacteria. The niche differentiation among these groups was strongly influenced by soil properties and plant traits, which in turn affect plant N uptake efficiency. In conclusion, we conducted a comprehensive analysis of the root‐mediated plant–microbe interactions and the regulated microbial N cycles in the rhizosphere soils of an acid subtropical forest. These findings are crucial for elucidating the biological mechanisms guiding microbial assembly in the rhizosphere and refining biological strategies to mitigate N loss in forest ecosystems. Read the free Plain Language Summary for this article on the Journal blog.