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Aims: Although plant–microbial interactions are essential to sustain terrestrial ecosystem functions, root–microbial interactions remain poorly understood. Therefore, understanding how functional trait diversity of fine roots mediates soil microbial diversity and composition provides insightful information to maintain forest ecosystem functions. Methods: A total of 87 plots with 1–12 tree species richness gradient in three subtropical secondary forests were selected. Functional trait diversity (functional dispersion, FDis, and community-weighted mean, CWM) of fine roots was quantified. Soil microbial diversity and community composition were analyzed by high-throughput Illumina sequencing. Results: Bacterial and fungal richness was primarily predicted by CWM of root diameter (CWM_diam) in the humus horizon, but by FDis of specific root length (FDis_SRL) in the mineral horizon. Microbial community composition in two soil horizons increased with FDis_SRL, including the abundance of copiotrophic bacteria (r-strategists, e.g., Proteobacteria, Actinobacteria), Chloroflexi, saprotrophs and pathogens. FDis_SRL was also indirectly mediated microbial richness and composition via decreasing carbon:nitrogen ratio and increasing pH, total nitrogen, total and available phosphorus contents. Conclusions: Overall, functional trait diversity of fine roots plays a pivotal role in mediating soil microbial richness and community composition in subtropical secondary forests. These results deepen our understanding of the important role of plant–microbial interactions in terrestrial biogeochemical processes. [ABSTRACT FROM AUTHOR]

Aims: There is evidence that different facets of biodiversity such as species richness (SR), phylogenetic diversity (PD) and functional diversity (FD) can modulate ecosystem functioning via niche-complementarity or mass-ratio effects, but the support for these hypotheses on fine root biomass remains unclear. Methods: In a tree diversity gradient in subtropical forests (ranging from 2 to 10 tree species), we identified the species identity of fine roots (≤ 2 mm in diameter) using a molecular method. This allowed computation of PD as well as trait-based FD and community-weighted means (CWM) metrics, which were then tested as predictors of fine root biomass. Results: Three metrics (SR, CWM of specific root length and PD) were positively related to root biomass. SR was the best predictor of fine root biomass and its predicting ability depended on stand density. The predicting power of CWM of specific root length varied with the soil nutrient status. Conclusions: Overall, the results supported both tested hypotheses (mass-ratio and niche-complementarity) that seem to be non-mutually exclusive. Furthermore, our findings emphasize that stand density and soil nutrient status are the important variables driving fine root biomass and trait-values. [ABSTRACT FROM AUTHOR]

Aims: The phylogenetic variations of fine root traits, which are related to plant growth and development as well as to physiological and ecological processes, are not fully understood. This study aimed to: (1) examine how tree species and sampling methodology affect the anatomical, morphological and nutrient traits of fine roots; and (2) determine whether phylogenetic signals affect fine root trait relationships and influence comparison of root traits between the branch order-based and diameter-based cut-off sampling categories.Methods: Fine root samples of 16 subtropical forest tree species were obtained and their anatomical, morphological and nutrient traits were studied. The phylogenetic signals of trait variations were calculated to determine trait relationships.Results: Tree species and sampling methodology significantly affected fine root traits (p < 0.05). Mean root diameters, root tissue density (RTD) and carbon-to-nitrogen ratio were the lowest in the first-order category and highest in the ≤2 mm category. The reverse pattern was found for specific root length, specific root area and nitrogen concentration. Morphological traits showed significant phylogenetic signals; however, nutrient traits did not reflect phylogenetic conservatism. Phylogenetic factors influenced correlations between traits for the first-order root economics spectrum. Root traits were multidimensional and RTD was loaded on a novel phylogenetic principal component analysis.Conclusions: Functional traits of fine roots are multidimensional for subtropical tree species and closely linked to phylogeny. Morphological traits of first order roots showed a much stronger phylogenetic signal than those of roots ≤2 mm (traditionally defined fine roots). The findings improve understanding of root trait strategies in response to environmental changes. [ABSTRACT FROM AUTHOR]

Aims: Our study aimed to determine whether, and to what extent, stand characteristics and topography affected spatial variations in soil organic carbon (SOC), total nitrogen (TN) and total phosphorus (TP) concentrations in subtropical forests. Methods: Soil samples were taken from a Choerospondias axillaris deciduous broadleaved forest and a Lithocarpus glaber-Cyclobalanopsis glauca evergreen broadleaved forest. Spatial variations in SOC, TN and TP concentrations and the factors affecting them were investigated using geostatistical analysis and stepwise linear regression, respectively. Results: The L. glaber-C. glauca forest exhibited higher coefficients of variation (CVs) of SOC (35 %) and TN (34 %) concentrations than the C. axillaris forest (27 % for SOC and 21 % for TN), but the CV of TP concentration in the L. glaber-C. glauca forest (17 %) was lower than that in the C. axillaris forest (24 %). Stand characteristics contributed the most to spatial variations in SOC and TP, while soil texture made the greatest contribution to variations in TN. Topography contributed the least to variations in SOC, TN and TP. Conclusions: Stand characteristics, together with topography and soil texture, contributed to spatial variations in SOC, TN and TP concentrations. The contributions of stand characteristics differed in SOC, TN and TP due to their different cycling characteristics. [ABSTRACT FROM AUTHOR]