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Abstract Mycorrhizal associations of trees play a key role in ecosystem biogeochemistry, yet we know relatively little about the nutrient acquisition strategies of ericoid mycorrhizal (ErM) shrubs, despite their prevalence in forest understories. ErM shrubs tend to produce litter with high concentrations of polyphenols, which form decay‐resistant complexes with organic nitrogen (N). Some ErM fungi appear capable of producing a diverse suite of extracellular enzymes, but it is unclear whether this enables ErM shrubs to acquire the N from their own litter, and whether this ability is greater than that of ectomycorrhizal (EcM) trees, with which they commonly co‐occur. Here, we conducted two growth chamber experiments with 15N‐enriched root and leaf litters to determine whether EcM pine and ErM vaccinium differ in litter N acquisition from these sources. Grown individually, pine and vaccinium plants acquired 1 mg or 4% of the litter N after one year. Differences between pine and vaccinium in litter N acquisition were correlated with litter chemistry, where vaccinium acquired more N from litter with a high concentration of tannins and a high C:N, while pine acquired more N from litter with a high acid‐insoluble fraction. When plants were grown in pairs, the presence of a vaccinium neighbor reduced the biomass of both species by an average of 24%, but it only reduced litter N acquisition by pine (55%), demonstrating vaccinium's ability to compete with pine for litter N. Regardless of the competitive context, vaccinium allocated a greater percentage (76%) of its acquired litter N to aboveground biomass compared with pine (47%), suggesting vaccinium is more efficient at allocating this N to photosynthesis and growth. Our finding that EcM pine and ErM vaccinium have varying abilities to acquire N from these common litters suggests a degree of niche complementarity, which may facilitate the coexistence of these plants in forest ecosystems. However, our results also suggest that, at high densities, ErM vaccinium has the potential to suppress the growth and N acquisition of EcM pine. Distinct strategies of EcM trees and ErM shrubs for acquiring and using N have the potential to shape biogeochemical cycles of many forested ecosystems.

Abstract Plant diversity has long been assumed to predict soil microbial diversity. However, contradictory results have been found when examining their relationships, particularly at broad spatial scales. To address this issue, we conducted a meta‐analysis to evaluate the patterns in the correlation between plant diversity and soil microbial diversity and the underlying factors driving the relationship. We collected correlation data from 84 studies covering more than 3900 natural terrestrial samples globally. Using the hierarchical mixed‐effects model, we investigated factors including targeted taxonomic group, microbial examination method, sampling extent, biome type, soil type, and environmental factors to assess the patterns of the plant–microbial correlation and the determinants of their variations. We found that microbial richness displayed a modest but positive correlation with plant diversity (r = 0.333, CI = 0.220–0.437). In spite of variability among taxonomic groups and their relationship with plant diversity, positive correlations were more pronounced in the intermediate sampling extent of latitude and elevation coverage, and tropical forests. Among examined environmental factors, soil pH was negatively associated with the plant and soil microbial relationships at large spatial scales. The plant–microbial correlation appears more sensitive to edaphic factor variation in the poor nutrients and soil less compact systems. Collectively, our results point to key differences across taxonomic groups, spatial scales and biomes, and the modulating effects of climate and soil. The findings shed light on our deep understanding in plant–microbial diversity relationships at broad spatial scales and ecosystem sensitivity to biodiversity loss and environmental change.