Search

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]

Background: Forest ecosystems play an important role in carbon sequestration, climate change mitigation, and achieving China's target to become carbon (C) neutral by 2060. However, changes in C storage and net primary production (NPP) in natural secondary forests stemming from tree growth and future climate change have not yet been investigated in subtropical areas in China. Here, we used data from 290 inventory plots in four secondary forests [evergreen broad-leaved forest (EBF), deciduous and evergreen broad-leaved mixed forest (DEF), deciduous broad-leaved forest (DBF), and coniferous and broad-leaved mixed forest (CDF)] at different restoration stages and run a hybrid model (TRIPLEX 1.6) to predict changes in stand carbon storage and NPP under two future climate change scenarios (RCP4.5 and RCP8.5). Results: The runs of the hybrid model calibrated and validated by using the data from the inventory plots suggest significant increase in the carbon storage by 2060 under the current climate conditions, and even higher increase under the RCP4.5 and RCP8.5 climate change scenarios. In contrast to the carbon storage, the simulated EBF and DEF NPP declines slightly over the period from 2014 to 2060. Conclusions: The obtained results lead to conclusion that proper management of China's subtropical secondary forests could be considered as one of the steps towards achieving China's target to become carbon neutral by 2060. [ABSTRACT FROM AUTHOR]

Canopy interception loss is an important hydrological process that affects rainfall redistribution, nutrient cycling, and soil and water conservation in forest ecosystems. However, the manner in which interception loss is affected in forests that are in restoration stages dominated by different tree species has not been fully understood. In this study, interception loss, throughfall, and stemflow were measured consecutively for 2 years (May 2017 through April 2019) in three secondary forests in subtropical China: a coniferous and broadleaved mixed forest (Pinus massoniana, Lithocarpus glaber, PM) in early restoration stage, a deciduous broadleaved forest (Choerospondias axillaris, CA) in middle restoration stage, and an evergreen broadleaved forest (L. glaber–Cyclobalanopsis glauca, LG) in late restoration stage. For a given amount of rainfall, the relative interception loss in the CA was significantly lower than that in the evergreen forests in summer, spring, or winter. The amount of interception loss during light rain, moderate rain, or heavy storms was also significantly lower in CA as compared to that in evergreen forests, owing to the lesser leaf area and phenology of deciduous tree species as well as a higher leaf area index (LAI) and stand density in PM and LG. Meanwhile, the highest relative interception loss, interception loss amount, canopy storage capacity, canopy cover fraction, and mean evaporation rate was observed in the climax forest (LG), which has a higher LAI and stand density. Further, the revised Gash's analytical model (RGAM) and the sparse Rutter models were successfully applied to simulate interception loss in these forests, with the RGAM performing better as compared to the sparse Rutter model. The results of the field measurements and model simulations depict that the climax community at the late restoration stage can effectively reduce the amount of rainwater reaching the soil surface, thus weakening the effect of flood peaks. [ABSTRACT FROM AUTHOR]

The importance of species richness to ecosystem functioning and services is a central tenet of biological conservation. However, most of our theory and mechanistic understanding is based on diversity found aboveground. Our study sought to better understand the relationship between diversity and belowground function by studying root biomass across a plant diversity gradient. We collected soil cores from 91 plots with between 1 and 12 aboveground tree species in three natural secondary forests to measure fine root (≤ 2 mm in diameter) biomass. Molecular methods were used to identify the tree species of fine roots and to estimate fine root biomass for each species. This study tested whether the spatial root partitioning (species differ by belowground territory) and symmetric growth (the capacity to colonize nutrient‐rich hotspots) underpin the relationship between aboveground species richness and fine root biomass. All species preferred to grow in nutrient‐rich areas and symmetric growth could explain the positive relationship between aboveground species richness and fine root biomass. However, symmetric growth only appeared in the nutrient‐rich upper soil layer (0–10 cm). Structural equation modelling indicated that aboveground species richness and stand density significantly affected fine root biomass. Specifically, fine root biomass depended on the interaction between aboveground species richness and stand density, with fine root biomass increasing with species richness at lower stand density, but not at higher stand density. Overall, evidence for spatial (i.e. vertical) root partitioning was inconsistent; assumingly any roots growing into deeper unexplored soil layers were not sufficient contributors to the positive diversity–function relationship. Alternatively, density‐dependent biotic interactions affecting tree recruitment are an important driver affecting productivity in diverse subtropical forests but the usual root distribution patterns in line with the spatial root partitioning hypothesis are unrealistic in contexts where soil nutrients are heterogeneously distributed. [ABSTRACT FROM AUTHOR]

To quantify and assess the processes underlying community assembly and driving tree species abundance distributions(SADs) with spatial scale variation in two typical subtropical secondary forests in Dashanchong state‐owned forest farm, two 1‐ha permanent study plots (100‐m × 100‐m) were established. We selected four diversity indices including species richness, Shannon–Wiener, Simpson and Pielou, and relative importance values to quantify community assembly and biodiversity. Empirical cumulative distribution and species accumulation curves were utilized to describe the SADs of two forests communities trees. Three types of models, including statistic model (lognormal and logseries model), niche model (broken‐stick, niche preemption, and Zipf‐Mandelbrodt model), and neutral theory model, were estimated by the fitted SADs. Simulation effects were tested by Akaike's information criterion (AIC) and Kolmogorov–Smirnov test. Results found that the Fagaceae and Anacardiaceae families were their respective dominance family in the evergreen broad‐leaved and deciduous mixed communities. According to original data and random sampling predictions, the SADs were hump‐shaped for intermediate abundance classes, peaking between 8 and 32 in the evergreen broad‐leaved community, but this maximum increased with size of total sampled area size in the deciduous mixed community. All niche models could only explain SADs patterns at smaller spatial scales. However, both the neutral theory and purely statistical models were suitable for explaining the SADs for secondary forest communities when the sampling plot exceeded 40 m. The results showed the SADs indicated a clear directional trend toward convergence and similar predominating ecological processes in two typical subtropical secondary forests. The neutral process gradually replaced the niche process in importance and become the main mechanism for determining SADs of forest trees as the sampling scale expanded. Thus, we can preliminarily conclude that neutral processes had a major effect on biodiversity patterns in these two subtropical secondary forests but exclude possible contributions of other processes. [ABSTRACT FROM AUTHOR]

[Display omitted] • Tree mycorrhizal dominance drives soil P bioavailable in subtropical forests. • Available inorganic P but not organic P increased with ECM tree dominance. • AM and ECM forest soil had similar activity of acid phosphatase. • ECM tree dominance increases leaf litter C/N ratio but decreased soil pH. Many forest tree species form symbiotic associations with either arbuscular mycorrhizal (AM) or ectomycorrhizal (ECM) fungi to increase access to nutrients. ECM and AM differ in strategies for acquiring nitrogen (N) and phosphorus (P), however, little is known about the degree to which mycorrhiza mediate the effects of tree species on soil P bioavailability outside of the temperate zone. Here, we established a natural gradient with increasing ECM tree dominance in subtropical secondary forests, and investigated the linkages between the ECM tree dominance and soil bioavailable P content. We quantified the contents of four soil bioavailable P pools (CaCl 2 -P, citric-P, enzyme-P and HCl-P) using the recently developed biologically-based P extraction method, as well as acid phosphatase activity, litter biomass and quality, microbial biomass carbon (C), and soil abiotic variables. We found that CaCl 2 -P, citric-P and HCl-P increased with ECM tree dominance, while enzyme-P did not. Specially, ECM-dominated soils displayed markedly higher (1.2–2.9 times) citric-P and HCl-P than AM soils, indicating that ECM forests can effectively obtain inorganic P by releasing organic acids and through proton excretion. The acid phosphatase involved in the acquisition of organic P had similar activity between AM and ECM forests. Structural equation models indicated that increasing ECM tree dominance increases litter C/N ratio and soil organic matter, but decreases pH and microbial biomass C/P ratio, all of which are critical in mediating P bioavailability. Collectively, our findings confirm that tree mycorrhizal associations affect soil P bioavailability, which have implications for understanding species coexistence and guiding forest managements in subtropics. [ABSTRACT FROM AUTHOR]

• Late stage forest supplied higher overall and more evenly distributed ES benefits. • Magnitudes of trade-offs between paired ESs changed with restoration stages. • The beneficiary in several paired trade-offs changed along the restoration gradient. • Tree functional groups are important to ES trade-offs and ecosystem management. Secondary forests have received more attention in recent decades because their total area is increasing and the greater recognition of ecological and economical benefits provided by forest ecosystems. Therefore, the Chinese government has given high priority to implementing its Natural Forest Program that includes the restoration of degraded secondary forests. Hence, how ecosystem services (ESs) and their trade-offs are altered during the restoration process of secondary forests merits research. Here, we selected five key ecological indicators of forests, namely plant diversity and four ESs—air quality regulation, maintenance of soil fertility, global climate regulation, and timber provisioning—to examine the trends and patterns in the variation of multiple indicators and their trade-offs during forest restoration. Furthermore, secondary forests in subtropical China are characterized by a diverse tree species community that transitions from conifers in the early stage of restoration, to deciduous broadleaf and evergreen broadleaf species in its mid and late stages; this provides an excellent opportunity to investigate the influences of different tree functional groups on ESs and the trade-offs among them. Our results showed that late-forest had a greater capacity to supply higher and more evenly distributed benefits of ESs than did early or mid-stage restored forests. We also found that the magnitude of trade-offs between paired ESs changed with the stage of restoration. Furthermore, the variation of the beneficiary in critical trade-offs corresponded to the patterns of change in benefits of specific ESs. Trade-offs between plant diversity and other ESs were significantly influenced by tree functional group, in that the deciduous broadleaved species had significant positive effects whereas the conifer and evergreen broadleaved species had negative effects. We conclude that accurate prediction and management of ESs in restoration forests should explicitly account for tree functional groups, in addition to the effects from combined trade-offs among multiple ESs. [ABSTRACT FROM AUTHOR]

• Mean concentration and annual output fluxes of DOC were the highest in the deciduous broadleaved forest. • Mean concentration of TDN tended to increase but annual TDN output fluxes decreased with forest restoration. • DOC cycle in the deciduous broadleaved forest was relatively open whereas TDN cycle turned to be closed as forest restored. In the restoration of subtropical forests, the hydrological fluxes of dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) have not been fully investigated in different stages dominated by different tree species. The concentrations of DOC and TDN in rainfall, throughfall, stemflow, and surface runoff were measured for two years in each of the three forests at different restoration stages: early coniferous forest (Pinus massoniana - Lithocarpus glaber), intermediate deciduous broadleaved forest (Choerospondias axillaris), and late evergreen broadleaved forest (L. glaber - Cyclobalanopsis glauca). Input and output fluxes as well as leaching and migration coefficients of DOC and TDN were calculated to examine the nutrient cycling status in the processes of forest restoration. In stemflow, DOC concentrations in the evergreen broadleaved forest differed significantly from those in the coniferous and deciduous broadleaved forests, whereas TDN concentrations differed significantly between the coniferous forest and other two forests. In throughfall, DOC and TDN concentrations were not significantly different among the three forests. The amount of DOC leached was primarily influenced by rainfall and was significantly related to fluxes in throughfall, with the highest value in the deciduous broadleaved forest (57.78 kg C ha−1). However, the amount of TDN leached was affected by rainfall and the absorption of vegetation and was not significantly related to fluxes in throughfall, except for the deciduous broadleaved forest. The highest value of TDN leached was in the coniferous forest (11.90 kg N ha−1). Mean TDN concentration in surface runoff tended to increase but annual TDN output fluxes decreased with forest restoration. However, both mean concentration and annual output fluxes of DOC in surface runoff were the highest in the deciduous broadleaved forest at the intermediate restoration stage. The concentrations were closely related to surface runoff, decomposition rate of litterfall, and soil organic matter content. The annual output fluxes of DOC and TDN in surface runoff were less than 30% of the input in throughfall, indicating nutrient accumulation in subtropical secondary forests. [ABSTRACT FROM AUTHOR]