Plant Root Traits Research Articles

Mitigation of Salt Stress in Lactuca sativa L. var. Gentile Rossa Using Microalgae as Priming Agents

Using renewable biomass in agriculture, particularly microalgae as a biostimulant, offers economic and environmental sustainability benefits by reducing costs, improving nutrient cycling, and enhancing water use efficiency. Microalgae contain bioactive compounds that boost crop tolerance to environmental stresses, including salinity. Saline soils, characterized by elevated sodium chloride (NaCl) levels, negatively impact many crops, resulting in low productivity and high remediation costs. Therefore, this study evaluates the biostimulant properties of a microalgae-based commercial preparation (MR) on lettuce (Lactuca sativa L.) plants grown hydroponically and exposed to saline stress. The extract was chemically characterized through elemental analysis, lipid composition (gas chromatography with flame ionization detector—GC-FID), the determination of functional groups (Fourier Transformed Infrared—FT-IR), structure (1H,13C Nuclear Magnetic Resonance—NMR), with their hormone-like activity also assessed. Lettuce plants were treated with or without the microalgae blend, in combination with 0, 50 mM, or 100 mM NaCl. The contents of nutrients, soluble proteins, chlorophylls, and phenols, as well as the lipid peroxidation, antioxidants and root traits of lettuce plants, were estimated. The microalgae applied to salt-stressed plants resulted in a significant increase in biomass, protein, and chlorophyll contents. Additionally, significant effects on the secondary metabolism and mitigation of salinity stress were observed in terms of increased phenol content and the activity of antioxidant enzymes, as well as decreased lipid peroxidation. The potassium (K+) content was increased significantly in plants treated with 100 mM NaCl after addition of microalgae, while the content of sodium (Na+) was concurrently reduced. In conclusion, our results demonstrate that using microalgae can be a potent approach for improving the cultivation of Lactuca sativa L. under saline stress conditions.

Invasive plants and their root traits are linked to the homogenization of soil microbial communities across the United States

Although the impacts of invasive plants on soil ecosystems are widespread, the role and impacts of invader root traits in structuring microbial communities remain poorly understood. Here, we present a macroecological study investigating how plant invaders and their root traits affect soil microbial communities, spanning data from 377 unique plots across the United States sampled multiple times, totaling 632 sampling events and 94 invasive plant species. We found that native and invasive plants harbor different root traits on average, with invasive plants possessing higher specific root lengths and native plants having higher root tissue density. We also show that soil microbial communities experiencing heavy plant invasions were more similar to each other in composition across ecosystem types and geographical regions than plots with higher proportions of native plants, which displayed highly variable microbial communities across the continent. Root traits of invasive plants in highly invaded plots explained two times more variation in microbial composition than native plants. This work represents an important step toward understanding macroscale and cross-scale patterns of the relationship between plant invasions, root traits, and soil microbial composition. Our findings provide insights into how invasive plants may impact ecosystem functioning at the macroscale via their homogenizing influence on microbial communities.

Effects of microplastics concentration on plant root traits and biomass: Experiment and meta-analysis

The impact of microplastics (MPs) on plant growth, particularly root development, remains underexplored. To address this, a laboratory pot experiment and meta-analysis were conducted to assess how varying concentrations of MPs affect plant root growth. In pot experiments, the response of root traits to MPs differed by plant species. For F. arundinacea, a higher addition (1 % and 2 %) of polypropylene (PP) significantly increased the total length, surface area, volume, as well as fine root (<1 mm) surface area and volume. Partial least squares path modeling (PLS-PM) analysis showed that high concentrations of MPs affected plant root growth and plant root biomass by promoting fine root growth. Meta-analysis indicated that MPs increased shoot dry biomass by 32.7 % but reduced root dry biomass by 4.1 % and root length by 14.3 %. Higher concentrations (>0.5 %) of MPs significantly increased root length (35.2 %) and root dry biomass (6.3 %), whereas decreased shoot dry biomass (-8.6 %). Under the lower MPs concentration (<0.5 %), the root length and root dry biomass were decreased by 18.6 % and 11.1 %, respectively, and the shoot dry biomass was increased by 53.2 % compared with the treatment without MPs. The results emphasize the differences in performance between species for different MPs concentrations, implying that there may be future scope to select for species/varieties that are most resilient to the presence of MPs.

Morphological Traits and Biomass Allocation of Leymus secalinus along Habitat Gradient in a Floodplain Wetland of the Heihe River, China

Plant organ biomass allocation and morphological characteristics are important functional traits. The responses of plant root, stem, and leaf traits to heterogeneous habitats in floodplain wetlands are highly important for understanding the ecological adaptation strategies of riparian plants. However, the patterns of these responses remain unclear. In a floodplain wetland in the middle reaches of the Heihe River, we studied the responses of the root, stem, and leaf morphological traits and biomass allocation of Leymus secalinus to varying habitat conditions. We measured these traits in three sample plots, delineated based on distance from the riverbank: plot I (near the riparian zone, 50–150 m from the riverbank), plot II (middle riparian zone, 200–300 m from the riverbank), and plot III (far riparian zone, 350–450 m from the riverbank). The results showed that in plot I, L. secalinus tended to have slender roots and stems and small leaves, with a biomass allocation strategy that maximized the root–shoot ratio (RSR). In plot II, L. secalinus had thick stems and moderate leaf and root patterns, and the RSR values were between those of plot I and plot III. In plot III, L. secalinus had thin and short stems and large leaves; furthermore, among the root morphological structures, plot III had the shortest Rhizome length (RL) and longest Rhizome diameter (RD), and the RSR was the lowest. Moreover, there was a significant correlation between organ biomass and leaf thickness, stem length, RD, and RL in the three habitats (p &lt; 0.05). By balancing the biomass allocation among organs, wetland plants in floodplains balance changes in root, stem, and leaf morphological characteristics to improve their environmental adaptation.

Effects of riparian pioneer plants on soil aggregate stability: Roles of root traits and rhizosphere microorganisms

Pioneer plants are vital in stabilizing soil structure while restoring reservoir drawdown areas. However, uncertainties persist regarding the mechanism of pioneer plants to soil stability in these delicate ecosystems. This study aims to unravel the plant-soil feedback mechanisms from the roles of root traits and rhizosphere microorganisms. We conducted a mesocosm experiment focusing on four common pioneer plants from the drawdown area of Three Gorges Reservoir, China. Using the wet sieving methodology, trait-based approach and high-throughput sequencing technology, we explored soil aggregate stability parameters, plant root traits and rhizosphere microbial communities in experimental plant groups. The interacting effect of pioneer plant species richness, root traits, and rhizosphere microbial communities on soil aggregate stability was quantified by statistical and machine-learning models. Our results demonstrate that diverse pioneer plant communities significantly enhance soil aggregate stability. Notably, specific species, such as Cynodon dactylon (L.) Pers. and Xanthium strumarium L., exert a remarkably strong influence on soil stability due to their distinctive root traits. Root length density (RLD) and root specific surface area (RSA) were identified as crucial root traits mediating the impact of plant diversity on soil aggregate stability. Additionally, our study highlights the link between increased rhizosphere fungal richness, accompanied by plant species richness, and enhanced soil aggregate stability, likely attributable to elevated RLD and RSA. These insights deepen our understanding of the role of pioneer vegetation in soil structure and stability, providing valuable implications for ecological restoration and management practices in reservoir drawdown areas.

Multi-dimensionality in plant root traits: progress and challenges

Multi-dimensionality in plant root traits: progress and challenges

A general pattern of plant traits and their relationships with environmental factors and microbial life-history strategies

The trait-based unidimensional plant economics spectrum provides a valuable framework for understanding plant adaptation strategies to the environment. However, it is still uncertain whether there is a general multidimensionality of how variation of both leaf and fine root traits are influenced by environmental factors, and how these relate to microbial resource strategies. Here, we examined the coordination patterns of four pairs of similar leaf and fine root traits of herbaceous plants in an alpine meadow at the community-level, and their environmental driving patterns. We then assessed their correlation with microbial life-history strategies, as these exhibit analogous resource strategies with plants in terms of growth and resource utilization efficiency. Results exhibited an analogous multidimensionality of the economics spectrum for leaf and fine root traits: the first dimension, collaboration gradient, primarily represented a tradeoff between lifespan and resource foraging efficiency; the second dimension, conservation gradient, primarily represented a tradeoff between conservation and acquisition in resource uptake. Climate variables had a stronger impact on both dimensions for leaf and fine root traits than soil variables did; whereas, the primary drivers were more complex for fine root traits than for leaf traits. The collaboration gradient of leaf and fine root traits exhibited consistent relationships with soil microbial life-history strategies, both showed negative and positive correlation with bacterial and fungal strategies, respectively. Our findings suggest that both leaves and fine roots have general multidimensional strategies for adapting to new environments and provide a solid basis for further understanding the relationships between the adaptive strategies of plants and microbes.

Variations in plant root traits shaped by intraspecific interactions are species-specific

Intraspecific plant interactions are crucial in terrestrial ecosystems, especially in artificially controlled ecosystems. Understanding plant root development can facilitate the manipulation of root traits to enhance the productivity and sustainability of agricultural and pastoral ecosystems. To date, most studies on interactions between the plants have focused on environmental factors or individual species; however, the lack of cross-species comparative analyses has resulted in a significant disparity in findings. In this study, we conducted a greenhouse experiment using five dominant species from alpine grasslands, including three legume species (Thermopsis lanceolata, Oxytropis ochrocephala, and Tibetia himalaica) and two grass species (Elymus nutans and Stipa aliena). Using single-plant cultivation as the control, we investigated the overall changes in plant biomass and root traits when two conspecific plants are grown together (intraspecifically). Simultaneously, we explored the differences in roots traits between the interaction and no-interaction zones. The results showed that, firstly, there was no significant difference in biomass and root traits of different zones when single-planted. But the impact of intraspecific interactions on neighboring plants exhibited significant species-specific. In terms of biomass and root traits (except for forks), E. nutans, T. lanceolata and T. himalaica responded significantly negatively to their neighbors. Whereas S. aliena and O. ochrocephala showed no significant changes and even positive responses. The overall trend of changes in the root zones, whether interactive or non-interactive, was consistent, either increasing or decreasing simultaneously, albeit to different extents. For instance, the difference between the interaction and no-interaction zones of T. lanceolata and O. ochrocephala was substantial, leading to allometric growth. Finally, our results showed poor correlations of physicochemical and nutrient factors with root traits in four of the five species, all except for E. nutans. Altogether, our findings confirmed that root trait variations resulting from intraspecific plant interactions are species-specific. These findings underscored the importance of species-specific in intraspecific plant interactions involving biological interactions among plants, which should be considered in future studies.

Variation and Correlation among Fine Root Traits of Desert Plants in Arid Areas of Northwest China

Variation and Correlation among Fine Root Traits of Desert Plants in Arid Areas of Northwest China

Root-associated fungi and acquisitive root traits facilitate permafrost nitrogen uptake from long-term experimentally warmed tundra.

Root-associated fungi (RAF) and root traits regulate plant acquisition of nitrogen (N), which is limiting to growth in Arctic ecosystems. With anthropogenic warming, a new N source from thawing permafrost has the potential to change vegetation composition and increase productivity, influencing climate feedbacks. Yet, the impact of warming on tundra plant root traits, RAF, and access to permafrost N is uncertain. We investigated the relationships between RAF, species-specific root traits, and uptake of N from the permafrost boundary by tundra plants experimentally warmed for nearly three decades at Toolik Lake, Alaska. Warming increased acquisitive root traits of nonmycorrhizal and mycorrhizal plants. RAF community composition of ericoid (ERM) but not ectomycorrhizal (ECM) shrubs was impacted by warming and correlated with root traits. RAF taxa in the dark septate endophyte, ERM, and ECM guilds strongly correlated with permafrost N uptake for ECM and ERM shrubs. Overall, a greater proportion of variation in permafrost N uptake was related to root traits than RAF. Our findings suggest that warming Arctic ecosystems will result in interactions between roots, RAF, and newly thawed permafrost that may strongly impact feedbacks to the climate system through mechanisms of carbon and N cycling.

Long-term fire and grazing regimes modify soil physical properties and root traits in North American tallgrass prairie

The native Konza tallgrass prairie is maintained by two key natural processes, periodic fire and ungulate grazing. As a potential crucial feedback mechanism, how fire and grazing influence plant root traits and soil properties in the tallgrass prairie ecosystem remains less known. Here, we investigated the effects of long-term fire and grazing regimes on soil physical properties and root traits at the Konza Prairie Biological Station, near Manhattan, KS, USA. Soil cores were collected under control (unburned and ungrazed), fire (annually burned), grazing (annually grazed), and fire + grazing (annually burned and grazed) treatments. Soil water retention, total root volume, specific root length, specific root area, and root biomass were measured. We found that both fire and grazing significantly reduced soil water retention, increased soil bulk density and soil microporosity (<50 μm), and reduced macroporosity (>50 μm) compared to the unburned and ungrazed treatment. Fire and grazing also significantly reduced litter accumulation by 79 % (burned), 57 % (grazed), and 77 % (burned and grazed). Fire increased specific root area by 15 %. Grazing and fire + grazing significantly decreased specific root length by 40 % and 29 %, and specific root area by 33 % and 24 %, respectively. Litter production was positively related to soil volumetric water content and soil pore volume of 300–50 μm, but negatively related to soil bulk density and soil pore volume of less 50 μm. Soil volumetric water content was positively correlated to specific root lengths, and soil bulk density was negatively related to specific root length and specific root area. There was a significant negative relationship between root diameter and soil volumetric water content under burned and grazed treatment. The SEM model showed that fire, grazing, and fire + grazing regimes were associated with dead root biomass (R2 = 0.38) and root length density (R2 = 0.40) indirectly through soil bulk density and litter accumulation. Our findings suggested that the annual fire + grazing regime seriously leads to the degradation of tallgrass prairie by influencing soil physical properties, reducing root trait functions and root biomass, and altering the relationship between root diameter and soil volumetric water content.

Broadleaf Trees Increase Soil Aggregate Stability in Mixed Forest Stands of Southwest China

In soils, high aggregate stability often represents higher quality and anti-erosion ability; however, few studies have systematically analyzed how different forest stands affect soil aggregate stability. We selected five typical mixed forest stands on Jinyun Mountain in Chongqing, China, as research sites to evaluate soil aggregate stability. Within these sites, we analyzed the factors influencing soil aggregate stability in different stands by measuring soil characteristics and root traits. Soil aggregation stability, plant root traits, and soil properties varied among the mixed forest stands. The broadleaf tree mixed forest improved soil aggregate stability by 57%–103% over that of the Pinus massoniana mixed forest. The soil organic carbon, cation exchange capacity, Fe-Al oxides, and fine root proportion were positively correlated with soil aggregate stability. The specific root length and very fine root proportion were negatively correlated with soil aggregate stability, whereas the fine root proportion was positively correlated with this property. Specifically, we found that arbuscular mycorrhizal fungi did not affect soil aggregate stability in acid rain areas. Structural equation modeling indicated that soil aggregate stability was closely related to soil physicochemical properties and plant root characteristics. Predictive factors accounted for 69% of the variation in mean weight diameter, and plant root traits influenced soil aggregate stability by affecting soil organic matter, texture, and Fe-Al oxides. This study elucidated the impact of soil physicochemical properties and plant root characteristics on soil aggregate stability in different forest stand types, which has crucial implications for optimizing the management of various forest types.

Maize, wheat, and soybean root traits depend upon soil phosphorus fertility and mycorrhizal status.

Strong effects of plant identity, soil nutrient availability or mycorrhizal fungi on root traits have been well documented, but their interactive influences on root traits are still poorly understood. Here, three crop species (maize, wheat and soybean) were grown under four phosphorus (P) addition levels (0, 20, 40 and 60mg P kg-1 dry soil), and plants were inoculated with or without five combined arbuscular mycorrhizal fungal (AMF) species. Plant biomass, nutrient contents, root traits (including total root length, average root diameter, specific root length and root tissue density) and plants' mycorrhizal responses were measured. Crop species, P level, AMF, and their interactions strongly affected plant biomass and root traits. P fertilization promoted plant growth but reduced mycorrhizal benefits on plant biomass and nutrient uptake. Root traits of maize were sensitive to P addition only under the non-mycorrhizal condition, whilst most root traits of soybean and wheat plants were responsive to mycorrhizal inoculation but not P addition. Mycorrhizal colonization reduced the root plasticity in response to P fertility for maize but not for wheat or soybean. This study highlights the importance of soil nutrient fertility and mycorrhizal symbiosis in influencing root traits.

Garden Waste Compost Tea: A Horticultural Alternative to Promote Plant Growth and Root Traits in Tomato (Solanum lycopersicum L.) Plants

The application of garden waste compost teas (CTs) in sustainable agriculture constitutes a biostimulant and environmentally friendly alternative. The purpose of this work was to study the physicochemical properties of three CTs prepared with different brewing processes (CT1, CT2, and CT3) immediately after extraction and six months later to determine whether those properties changed over time and evaluate the effect of CT application on tomato (Solanum lycopersicum L.) plant growth. The brewing process had a significant effect on the extracts’ chemical composition, while long-term storage did not lead to significant differences. The most energy-efficient CT was evaluated in a pot and in vitro assays by measuring plant growth parameters and root traits. CT1 directly supplied to the substrate increased the leaf number, plant height, and dry weight of tomato plants compared to the control and foliar treatments, whereas no significant differences were found among foliar treatments. In terms of the effects of CT application on root development, the results of the in vitro assays showed that CT supply enhanced the primary root length, lateral root number, and root fresh weight while decreasing shoot height and weight in 10-day-old tomato seedlings. From an agronomic standpoint, this study contributes new insights regarding the storage stability of CT and its impact on tomato plant growth.

Response of soil aggregate stability to plant diversity loss along an inundation stress gradient in a reservoir riparian zone

Dam-triggered periodic wetting and drying has increased the disintegration of soil particles in riparian areas. Most studies in this field have primarily explored the effects of vegetational characteristics on soil stability. However, the impact of plant diversity loss on the soil aggregate stability under periodic inundation stress remains unclear. This study investigated the relevant plant characteristics, root traits, and soil physicochemical properties in a typical riparian ecosystem along a hydrological stress gradient. Data-driven models were used to quantify the paths influencing soil aggregate stability through root traits under heterogeneous inundation stress. The findings showed that as inundation stress intensified, there was an overall decline in plant community diversity and soil aggregate stability in this riparian zone. Perennial herbs with fibrous root systems, as the dominant species, played an essential role in the subsurface soil aggregate stability under intense inundation stress, in contrast to the critical role of plant diversity under weak inundation stress. Moreover, the results revealed that root volume density and macroaggregate carbon content mediated the effects of plant diversity on riparian soil stability. Overall, the results suggest that suitable plants with high root volume density benefit essential soil aggregate stability under well-documented inundation effects in riparian zones.

Contrasting patterns of community-weighted mean traits and functional diversity in driving grassland productivity changes under N and P addition.

Fertilization could influence ecosystem structure and functioning through species turnover (ST) and intraspecific trait variation (ITV), especially in nutrient limited ecosystems. To quantify the relative importance of ITV and ST in driving community functional structure and productivity changes under nitrogen (N) and phosphorous (P) addition in semiarid grasslands. In this regard, we conducted a four-year fertilizer addition experiment in a semiarid grassland on the Loess Plateau, China. We examined how fertilization affects species-level leaf and root trait plasticity to evaluate the ability of plants to manifest different levels of traits in response to different N and P addition. Also, we assessed how ITV or ST dominated community-weighted mean (CWM) traits and functional diversity variations and evaluated their effects on grassland productivity. The results showed that the patterns of plasticity varied greatly among different plant species, and leaf and root traits showed coordinated variations following fertilization. Increasing the level of N and P increased CWM_specific leaf area (CWM_SLA), CWM_leaf N concentration (CWM_LN) and CWM_maximum plant height (CWM_Hmax) and ITV predominate these CWM traits variations. As a results, increased CWM_Hmax, CWM_LN and CWM_SLA positively influenced grassland productivity. In contrast, functional divergence decreased with increasing N and P and showed negative relationships with grassland productivity. Our results emphasized that CWM traits and functional diversity contrastingly drive changes in grassland productivity under N and P addition.

Targeted control of soil erosion through selective regulation of Eleocharis yokoscensis using mixed endophytes

Plant root traits play a crucial role in controlling soil erosion and environmental pollution. However, the mechanisms underlying their impact on erosion risks remain unclear due to a lack of effective methods for adjusting root characteristics. In this study, we successfully enhanced the root characteristics and root-soil binding capacity of Eleocharis yokoscensis by employing a combination of soaking and spraying with mixed endophytic bacteria. Experimental results on slopes of 15°, 30°, and 45° demonstrated the efficacy of the mixed endophytes (MIX2.1) treatment in reducing runoff by 23.9607 L/m2 (Quartz Soil), 61.6776 L/m2 (Sandy Soil), and 5.9841 L/m2 (Red Soil), respectively. Additionally, infiltration rates increased by 104% (Quartz Soil), 67% (Black Soil), and 86% (Red Soil), while sediment loads decreased by 86% (Quartz Soil), 70% (Black Soil), and 56% (Black Soil). To predict erosion prevention, we proposed and calibrated a novel method called the Root-Soil Cohesion Ratio (RSCR). Furthermore, weight and correlation analysis revealed intriguing relationships between root characteristics and soil erosion parameters, particularly on steeper slopes where some relationships were reversed. Specifically, the presence of endophytes increased root complexity, but the uncontrolled direction of fibrous roots disrupted rainwater descent channels, impeding infiltration. Conversely, the orientation of lateral roots in the soil positively influenced water infiltration. Moreover, smaller particle gaps in the soil hindered rainwater infiltration to a lesser extent under high slope conditions. In conclusion, selectively modulating plant root traits and regulating specific soil erosion parameters in conjunction with slope factors are vital for effective erosion control. The findings of this study offer valuable engineering implications for utilizing plants in erosion-prone areas to enhance land stability and contribute to erosion restoration efforts.

The effect of experimental warming on fine root functional traits of woody plants: Data synthesis

Fine root traits are critical to plant nutrition and water uptake, and soil nutrient cycling. The impacts of climate warming on woody plants are predicted to be severe, but the effects on the fine root traits of woody plants remain unclear. To evaluate the effects of warming on fine-root traits of woody plants, we synthesized 431 paired observations of 13 traits from 78 studies. The result showed that warming increased the fine root nitrogen (N) concentration, root mortality, and root respiration, but decreased fine root phosphorus (P) concentration, root C:N and root nonstructural carbohydrates (NSC) concentration. However, warming had no significant effect on fine root biomass, root production and morphological traits. Warming effects on fine root biomass and root diameter decreased with warming magnitude, while root P concentration increased. Moreover, with increasing warming duration, the effect size of specific root length (SRL), root length, root C:N and root NSC increased. The effects size of root biomass, root diameter, root length and root C:N decreased with mean annual temperature (MAT) and mean annual precipitation (MAP) increase. However, the effect size of root N concentration increased with higher MAT and MAP. Furthermore, warming increased the fine root biomass of ectomycorrhiza (ECM) plants, but decreased that of plants associated with arbuscular mycorrhizal (AM) fungi. These results indicate that the effect of warming on fine root traits of woody plants was not only modulated by warming duration and magnitude, but also MAT and MAP. Our findings highlight the differential warming responses to fine root traits of woody plants, which have strong implications for shrubs and tree-dominated ecosystems soil nutrients cycling and carbon stocks.

Are absorptive root traits good predictors of ecosystem functioning? A test in a natural temperate forest.

Trait-based approaches provide a useful framework to predict ecosystem functions under intensifying global change. However, our current understanding of trait-functioning relationships mainly relies on aboveground traits. Belowground traits (e.g. absorptive root traits) are rarely studied although these traits are related to important plant functions. We analyzed four pairs of analogous leaf and absorptive root traits of woody plants in a temperate forest and examined how these traits are coordinated at the community-level, and to what extent the trait covariation depends on local-scale environmental conditions. We then quantified the contributions of leaf and absorptive root traits and the environmental conditions in determining two important forest ecosystem functions, aboveground carbon storage, and woody biomass productivity. The results showed that both morphological trait pairs and chemical trait pairs exhibited positive correlations at the community level. Absorptive root traits show a strong response to environmental conditions compared toleaf traits. We also found that absorptive root traits were better predictors of the two forest ecosystem functions than leaf traits and environmental conditions. Our study confirms the important role of belowground traits in modulating ecosystem functions and deepens our understanding of belowground responses to changing environmental conditions.

Effects of tree diversity on soil microbial community in a subtropical forest in Southwest China

Soil microorganisms are crucial for biological diversity and ecosystem processes in terrestrial ecosystems. Plant diversity has been reported to have positive effects on microbial communities. However, further research is required to understand the complex mechanisms that regulate the interactions between plants and soil microorganisms, especially the corresponding variations in soil microbial communities under tree diversity gradients in natural forest ecosystems. Therefore, we conducted a field investigation in a natural subtropical forest and collected 45 soil samples to evaluate how the soil microbial biomass and community diversity (represented by phospholipid fatty acid biomarkers) responded to a tree diversity gradient as well as their associations with plant (root and litter) traits and soil variables. The contents of total PLFAs ranged from 86.4 to 325.5 nmol g−1 soil with an average of 183.2 ± 66.1 nmol g−1 soil across the 45 plots. Tree diversity significantly enhanced microbial biomass and decreased microbial diversity. Hierarchical partitioning analysis revealed that the soil substrates (including inorganic and organic nutrients) were the major determinants of microbial biomass. Structural equation models also demonstrated that the effects of tree diversity on the biomass and diversity of soil microbial communities were mainly dependent on soil substrates and soil water content, respectively. In addition, soil microorganisms may potentially metabolize relatively recalcitrant carbon components under low tree diversity, whereas they tended to utilize labile carbon sources under high tree diversity. Overall, these findings suggested that the soil microbial community biomass and diversity exhibited distinct changes along the tree diversity gradient, and highlighted the key role of soil substrates availability in controlling microbial biomass.