Search Results (73)

Climate models suggest that longer dry periods and heavier rainfall events may occur in arid and semiarid regions, which may greatly affect plant growth and propagation in these regions. Numerous studies have documented the relationship between grassland productivity and precipitation. However, the interactive effects of rainfall amount and rainfall frequency on the growth of perennial grasses with rhizomatous propagation, especially on clonal growth, have not yet been studied. In this study, the effects of three rainfall amounts and two rainfall frequencies on the vegetative traits and clonal growth traits of Leymus chinensis, a perennial rhizomatous species, were examined. Rainfall amount and rainfall frequency exhibited a significant interaction only for the root biomass ratio between the 0–20 cm and 20–40 cm soil layers. All traits (including height, aboveground biomass, root biomass, rhizome number, rhizome length, bud bank size, and daughter shoot number) increased markedly with increasing rainfall amount but showed little response to rainfall frequency. Only the root biomass in the 20–40 cm soil layer increased with an extended dry period between two rainfall events, resulting in a lower root biomass ratio between the 0–20 cm and 20–40 cm soil layers under the medium and high rainfall amount treatments. The size of the belowground bud bank was positively correlated with the daughter shoot number as well as the aboveground biomass, and the positive relationship between the bud bank size and daughter shoot number was strengthened with increasing rainfall amount, but was not sensitive to rainfall frequency. However, lower rainfall frequency significantly decreased the rhizome number per plant. These results highlight that summer rainfall amount is more important than rainfall frequency for the population growth of L. chinensis at medium and high rainfall amounts, and that lower rainfall frequency may reduce the long-term clonal growth ability of L. chinensis in the future. Our findings reveal the response mechanisms of L. chinensis productivity to climate change from the novel perspective of bud banks, which provides practical management insights for artificially established L. chinensis grasslands. This study also offers important implications for elucidating the contributions of belowground biomass production to soil carbon sequestration in grassland ecosystems. Full article

Subalpine grasslands (SGs) of the Loess Plateau in China play a crucial role in the global carbon cycle of terrestrial ecosystems. However, the distribution pattern of total carbon stores along an elevation gradient on the SG plants of the eastern plateau remains unclear. In this study, eight typical mountains with one well-developed SG being surveyed as plot for each mountain were selected along an elevation gradient from 1722 m to 2954 m on the east of the plateau. The vegetation area, hydrothermal factors, soil elements, and species composition were analyzed using methods of spatial analysis and a partial least squares structural equation model (PLS-SEM), and these were used to estimate the total carbon stores of different plant functional groups for the entire area of each SG. This study revealed the driving factors of the elevational pattern of plant carbon storage in the SGs. The entire plant carbon storage of the eight SGs was 35,880.98 Mg in total. In addition, the aboveground and belowground carbon storage values both exhibited U-shaped trends along the elevation gradient. Significant minimum values were observed at the mid-elevation regions, ranging from 2305 m to 2673 m. The plant carbon storage was predominantly allocated to the belowground portions (accounting for 72.3% of the total carbon storage), and this allocation strategy was more pronounced at both low- and high-elevation regions. The carbon storage proportion among the different plant functional groups was the largest for forbs (average in 2348.85 Mg, accounting for 52%), medium for sedges (average in 1982.81 Mg, accounting for 44%), and the smallest for grasses (average in 153.47 Mg, accounting for 4%). The plant species diversity promoted carbon accumulation in the sedges and forbs, while the soil total phosphorus exhibited an inhibitory effect. In the PLS-SEM, hydrothermal factors (total effect = −0.8107) and species diversity (total effect = 0.4969) were the primary drivers of the plant carbon storage elevational pattern in the SGs, while the soil properties (total effect = −0.3501) and biomass (total effect = 0.0697) effects did not reach statistical significances. Therefore, the plant carbon storage distribution pattern along the elevation gradient was driven by hydrothermal factors and species diversity on the SGs of the eastern plateau. The plants such as forbs and sedges might play more important roles in improving regional plant carbon storage in high-elevation grasslands, through interactions with hydrothermal factors. Full article

Alpine treeline and shrubline ecotones are climatically sensitive transition zones where vegetation shifts strongly influence belowground microbial processes. Soil bacteria and fungi, as core component of the soil microbiome, play vital roles in nutrient cycling and plant–soil interactions within these fragile ecosystems. However, the structure and diversity of soil microbial communities across the treeline–shrubline transition remain poorly understood. Here, we investigated soil bacterial and fungal communities across treeline and shrubline ecotones in two mountain on the eastern Tibetan Plateau. We further examined how soil physicochemical properties shaped microbial community assembly. Our results demonstrated that the community composition of both bacteria and fungi differed significantly between the treeline and shrubline ecotones, while the Shannon index showed no significant variation. At the phylum level, Proteobacteria, Actinobacteriota, and Acidobacteriota dominated bacterial communities, while Ascomycota and Basidiomycota were the predominant fungal phyla. Both the network complexity of soil bacterial and fungal communities changed significantly across ecotones. Specifically, bacterial network complexity increased significantly toward the shrubline, whereas fungal network complexity declined. Bacterial community compositions were co-regulated by both environmental and vegetation factors, while fungal community compositions were only regulated by soil pH. Redundancy analysis revealed that soil organic carbon, pH, and moisture were the primary drivers of bacterial community (38.17%), whereas vegetation cover, soil organic carbon, and moisture explained the largest proportion of fungal community (44.79%). Our findings reveal the distribution patterns and underlying shift mechanisms of microbial communities between the treeline and shrubline ecotone. These insights are crucial for mountain biodiversity conservation and for improving predictions of forest responses to climate change. Full article

While the effect of domestication on various aspects of plant ecophysiology has been studied, less is known about its effect on plant–soil interaction. Here, we studied three botanical species of barley in comparison with four old cultivars and four contemporary cultivars with bare soils and two perennial grasses. Aboveground and belowground biomass decreased from botanical species to old cultivars and contemporary cultivars. Aboveground biomass of all barley cultivars was about one third lower in mineral fertilizer compared to the organic one, and this difference was similar in all barley cultivars. Biomass of perennial grasses was up to one third of barley biomass, but grass biomass did not differ significantly between fertilization treatments. Belowground biomass of botanical barley is significantly higher than that of modern cultivars; this discrepancy is even more pronounced under mineral fertilizer where belowground biomass of botanical barley significantly increased, and that of modern cultivars significantly decreased in comparison with organic fertilizer treatment, which means that modern barley cultivar in combination with mineral fertilizers provides less belowground litter to soil. This in the long term can potentially, together with other factors, contribute to the depletion of cultivated soil for organic matter. Microbial respiration in soil did not differ between treatments supplied by organic fertilizer, while in mineral fertilizer treatments old cultivars had lower respiration than other treatments. Microbial biomass did not differ between treatments supplied by mineral fertilizer, but in treatments supported by organic fertilizer, perennial grasses supported more microbial biomass than all barley treatments. The same pattern was observed in C content in soil. Carbon distribution in individual soil fractions did not differ between perennial grasses and barley treatments. In general, when hotspots of organic matter were provided, plants transferred this organic matter to soil, and this activity was more pronounced in perennial grasses than in barley treatments. Full article

Quinoa (Chenopodium quinoa Willd.) is a strategic crop for climate-smart agriculture in the Andes, yet yield gains are constrained by soil degradation and low-input systems. We tested whether synergistic bioinoculation with a plant growth-promoting rhizobacterium (Azospirillum brasilense) and an arbuscular mycorrhizal fungus (Glomus iranicum var. tenuihypharum) enhances root function and grain productivity under field conditions. A split-plot RCBD was conducted in Ayacucho, Peru (2735 m a.s.l.) using four cultivars, Blanca de Junín (BJ), INIA 441 Señor del Huerto (SH), INIA 415 Pasankalla (RP) and INIA 420 Negra Collana (NC) and four treatments: uninoculated control, Azospirillum, Glomus and co-inoculation. Vegetative, root and yield traits were quantified; ANOVA, Tukey/Dunnett contrasts, correlations and PCA were applied. Co-inoculation consistently outperformed single inoculants, increasing root diameter, length, branching, dry weight and volume dry weight, while also enlarging panicle dimensions and raising grain weight per panicle and thousand-seed weight. Grain yield reached 4.94 ± 0.59 t ha⁻¹ under co-inoculation, almost triple that of the control (1.71 ± 0.28 t ha⁻¹) and about 1.5 times higher than single inoculations. Genotypic effects were pronounced; BJ and SH combined superior root biomass with higher yield, RP maximized grain size and hectoliter weight, whereas NC responded weakly. Significant genotype × treatment interactions indicated cultivar-dependent microbiome benefits. Correlation and PCA linked root biomass and stem/panicle architecture to yield formation, positioning co-inoculation along trait vectors associated with belowground vigor and productivity. These results demonstrate a robust microbial synergy that translates root gains into yield, supporting co-inoculation as a scalable, low-input strategy for sustainable intensification of quinoa in highland agroecosystems. Full article

Chinese fir (Cunninghamia lanceolata) is a cornerstone timber species in southern China. However, yet its plantation productivity frequently declines under successive rotations, threatening long-term sustainability. While belowground processes are suspected drivers, the mechanisms—particularly plant–soil–microbe interactions—remain poorly resolved. To address this, we examined a chronosequence of C. lanceolata plantations (5, 15, 20, and 30 years) in Jingdezhen, Jiangxi Province, integrating soil physicochemical assays, high-throughput sequencing, and extracellular enzyme activity profiling. We found that near-mature stands (20 years) exhibited a 60.7% decline in mean annual volume increment relative to mid-aged stands (15 years), despite continued increases in individual tree volume—suggesting a strategic shift from resource-acquisitive to nutrient-conservative growth. Peak values of soil organic carbon (32.87 g·kg⁻¹), total nitrogen (2.51 g·kg⁻¹), microbial biomass carbon (487.33 mg·kg⁻¹), and phosphorus (25.65 mg·kg⁻¹) coincided with this stage, reflecting accelerated nutrient turnover and intensified plant–microbe competition. Microbial communities shifted markedly over time: Basidiomycota and Acidobacteria became dominant in mature stands, replacing earlier Ascomycota and Proteobacteria. Random Forest and Partial Least Squares Path Modeling (PLS-SEM) identified total nitrogen, ammonium nitrogen, and total phosphorus as key predictors of productivity. PLS-SEM further revealed that stand age directly enhanced productivity (β = 0.869) via improved soil properties, but also indirectly suppressed it by stimulating microbial biomass (β = 0.845)—a “dual-effect” that intensified nutrient competition. Fungal and bacterial functional profiles were complementary: under phosphorus limitation, fungi upregulated acid phosphatase to enhance P acquisition, while bacteria predominately mediated nitrogen mineralization. Our results demonstrate a coordinated “soil–microbe–enzyme” feedback mechanism regulating productivity dynamics in C. lanceolata plantations. These insights advance a mechanistic understanding of rotation-associated decline and underscore the potential for targeted nutrient and microbial management to sustain long-term plantation yields. Full article

Numerous studies have shown that there are many uncertainties associated with the interactions of nitrogen with plants and microorganisms. In particular, the effects of symbioses between plants and various microorganisms on soil microbial community function remain unclear. Metagenomic sequencing was used to explore the changes in microbial community composition, function and metabolic pathways in rhizosphere soil and the associated influencing factors under different nitrogen levels caused by arbuscular mycorrhizal fungi (AMF) inoculation of F. rubra infected with endophytic fungi and nonendophytic fungi. Plant nutrient allocation (aboveground/belowground), soil pH, and enzymatic activities significantly modulated the functional profiles of the bacterial, fungal, and archaeal communities within these rhizospheres. Soil β-glucosidase activity had the greatest effect on the cluster of orthologous groups of proteins (COG) function of the rhizosphere soil bacterial community, and soil L-leucine aminopeptidase had the greatest effect on the COG function of the rhizosphere soil fungal and archaeal communities. The contributions of AMF colonization to the kyoto encyclopedia of genes and genomes (KEGG) functions of bacteria and archaea in the rhizosphere soil were greater than those of F. rubra infection with endophytic fungi, and AMF colonization improved the metabolic pathways, secondary metabolite biosynthesis, microbial metabolism, amino acid biosynthesis and carbon metabolism of bacterial and archaeal communities in the rhizosphere soil of F. rubra. The effects of endophytic fungi and AMFs on the function and metabolic pathways of symbiotic rhizosphere soil microbial communities were heterogeneous. This study revealed that considering both biotic and abiotic factors is essential for predicting the maintenance of soil ecosystem function by plant–fungal symbionts. Full article

In situ observations of belowground tree–grass interactions are sparse in savanna ecosystems. In this study, we analyzed stable carbon and nitrogen isotopes (δ¹³C and δ¹⁵N) in soils and plants from four study sites in an African savanna ecosystem along the Kalahari moisture gradient. The homogeneous soil texture, primarily sandy soils, is well-drained and nutrient-poor, influencing vegetation and water retention uniformly across the region. At each site, soil samples were collected from a 120 cm deep soil profile. We used a 2-endmember mass balance approach to calculate the relative contributions of C₃ and C₄ plants to SOC in the 120 m soil profile. The wettest site was dominated by trees, whereas the driest site was dominated by shrubs. The intermediates had the highest amount of grass biomass. Our results revealed that tree- and shrub-derived SOC was highest in the wettest and driest sites, respectively. The contribution of C₃ plants was 63.8% and 55.8%, in the wettest and driest sites, respectively, when integrating the 120 cm depth. Grass-derived SOC was highest (69.4%) in the middle of the precipitation gradient when integrating the 120 cm depth. The δ¹⁵N values were highest in the middle of the precipitation gradient (10.7‰) and lowest in the wettest site (5.2‰). Our findings indicate that belowground tree–grass interactions and nitrogen cycling in savanna ecosystems are more complex than previously thought and do not conform to the traditional concept of the two-layer roots hypothesis. This lack of conformity could be attributed to several factors, including overlap in rooting depth and ecological drivers, such as wildfires and herbivory, which could stimulate production of belowground biomass. We used space-for-time substitution to leverage the region’s steep north–south precipitation gradient and homogeneous soil texture. Our results indicated that trees and shrubs would become an important SOC source in the two extreme sites of the transect, while grass would become an important SOC source in the middle of the precipitation gradient. Full article

Grass–legume mixtures are increasingly recognized for their potential to enhance soil health and forage productivity through belowground biotic interactions. In this study, we evaluated the effects of Vicia faba L. (faba bean 4060)–Avena sativa L. (oat ‘Baylor II’) mixtures on biomass, soil properties, and bacterial community dynamics. Results showed that mixtures significantly reduced the fresh weight of faba bean (6.2 kg/m²) compared to monoculture (8.8 kg/m², p < 0.001), while oat biomass increased under mixtures (3.2 kg m⁻² vs. 2.8 kg m⁻², p < 0.01). Available phosphorus (AP) and available potassium (AK) significantly decreased in the rhizosphere of both mixtures, whereas alkali-hydrolyzable nitrogen (AN) significantly increased, particularly in oat. Mixtures significantly enhanced bacterial richness, evenness, and Shannon diversity in faba bean (p < 0.01) but had no significant effect on oat diversity metrics. NMDS indicated distinct shifts in bacterial community structures under mixtures. Acidobacteriota and Vicinamibacteraceae were enriched in faba bean mixtures, whereas Actinobacteriota decreased in both forages under mixtures. Source Tracker analysis suggested substantial microbial exchange between species, with over 40% of the bacterial community in mixed roots originating from the partner monoculture. Although microbial community stability tended to decline under mixtures, differences were not significant. Niche breadth was significantly expanded in faba bean mixtures. Community assembly processes remained predominantly stochastic; however, mixtures slightly shifted the balance toward deterministic processes. Structural equation model revealed that soil physicochemical properties had a significant negative effect on diversity (β = −0.371, p = 0.007), and diversity had a significant negative effect on freshweight (β = −0.770, p < 0.001), suggesting that bacterial diversity may play a mediating role in the relationship between soil properties and plant fresh weight (β = 0.285, p = 0.011). These findings demonstrate that mixture-induced changes in soil nutrient status and microbial community characteristics collaboratively mediate plant performance through altered community assembly and diversity–function relationships. Full article

Rhizosphere microbiota are key drivers of plant nutrition, immunity, and stress tolerance. Abies ziyuanensis L. K. Fu & S. L. Mo (Pinaceae) is an endangered conifer endemic to China, and its persistence may depend on its interactions with its belowground microbiome. However, how soil-borne bacterial functional groups respond to, and potentially support, A. ziyuanensis remains unclear. Based on amplicon high-throughput sequencing data of the 16S rRNA gene and soil physicochemical properties, the bacterial community structure in the rhizosphere soil of A. ziyuanensis in Yinzhu Laoshan National Nature Reserve in Guangxi Zhuang Autonomous Region, China, was analyzed, and the potential ecological functions and phenotypic characteristics of the bacterial community were predicted to determine the functional taxa characteristics (nitrogen cycle, phototrophy, and chemoheterotrophy) and dominant soil environmental factors. Proteobacteria, Acidobacteria, Actinobacteria, Planctomycetes, Verrucomicrobia, and Chloroflexi were the dominant bacterial taxa in the A. ziyuanensis rhizosphere soil, and all bacteria were significantly positively correlated with soil NO₃⁻-N (R = 0.47, p = 0.0079). Based on FAPROTAX, the A. ziyuanensis rhizosphere soil bacterial community had chemoheterotrophic-related functions, which were more prevalent than nitrogen cycle- and phototrophic-related functions, and the relative abundance of bacteria with nitrogen cycle-related functions was higher than that of those with phototrophic functions. The nitrogen nutrient- and phototrophic-related functional taxa in the rhizosphere soil bacterial community had significant correlations with soil physicochemical properties, whereas the chemoheterotrophic-related functional taxa did not show a significant correlation. Based on BugBase phenotype prediction, Acidobacteria, Proteobacteria, and Chloroflexi made the greatest contribution to the phenotype, with pathogenic and stress tolerance being the most important phenotypes. The pathogenic and stress-tolerant bacteria all belonged to Proteobacteria. The rhizosphere bacteria exhibited rich diversity and dominated several biogeochemical cycling processes. This study identifies beneficial rhizosphere bacteria of A. ziyuanensis, providing a theoretical basis for conserving soil bacterial diversity and guiding the targeted recruitment of functional bacteria by the endangered plant. Full article

Mulching is a sustainable agronomic practice that can improve soil quality and fruit characteristics in crops. This study investigated the influence of sheep wool mulch and a soil conditioner on growth, the accumulation of bioactive compounds, and soil enzymatic activity in apple orchards. A two-year field experiment (2023–2024) was conducted using three experimental methods: mulching with sheep wool (V2), application of a soil conditioner, corn starch-based polymer (V3), and a combination of sheep wool and corn starch-based polymer (V4) along with a control (V1). Tree growth parameters, fruit physicochemical properties, total phenolic and flavonoid content, and soil enzyme activities (dehydrogenase, catalase, phosphatase) were assessed. Data were analyzed using Principal Component Analysis (PCA) and Pearson’s correlation. PCA showed that the combined variant (V4) improved fruit size, weight, and bioactive compound content, while wool mulch alone (V2) was associated with higher fruit yield and better vegetative growth. Catalase activity correlated positively and consistently with bioactive compounds in both years, while phosphatase activity showed an intensified positive relationship in 2024. Dehydrogenase activity was negatively correlated with phenolic content in both seasons. Organic and integrated mulching practices can beneficially modulate both aboveground and belowground plant–soil interactions. The combined variant proved to be the most effective strategy, enhancing fruit nutritional quality and supporting sustainable apple orchard management. Full article

Microplastic pollution threatens coastal wetland ecosystems, yet its impacts on the dominant plant species and soil properties remain poorly understood. We investigated the effects of four microplastic types (PP, PE, PS, PET) at three concentrations (0.1%, 0.5%, 1% w/w) on Scirpus mariqueter, a keystone species in the coastal wetlands of China, and the associated soil physicochemical properties. In a controlled pot experiment, microplastics significantly altered the plant biomass, vegetative traits, and reproductive strategies, with type-specific and concentration-dependent responses. PET and PE strongly suppressed the belowground and total biomass (p < 0.05), with reductions in the belowground biomass of 42.87% and 44.13%, respectively, at a 0.1% concentration. PP promoted seed production, particularly increasing the seed number by 25.23% at a 0.1% concentration (p < 0.05). The soil NH₄⁺-N, moisture, and EC were key mediators, with NH₄⁺-N declines linked to biomass reductions via nitrogen limitation. The Spearman correlations confirmed strong associations between the plant traits and soil properties, particularly nitrogen forms. These findings reveal that microplastics disrupt wetland plant performance and soil environments, potentially impairing carbon sequestration and ecosystem stability. Our study underscores the urgent need for microplastic risk assessments in coastal wetlands and highlights soil–microbe–plant interactions as critical mechanisms for future investigation. Full article

Soil saline–alkaline stress and water stress, exacerbated by anthropogenic activities and climate change, are major drivers of wetland vegetation degradation, severely affecting the function of wetland ecosystems. In this study, we conducted a simulation experiment with three water levels and four saline–alkaline concentration levels as stress factors to assess eight key functional traits of Phragmites australis and Bolboschoenus planiculmis, dominant species in the salt marsh wetlands in the western region of Jilin province, China. The study aimed to evaluate how these factors influence the functional traits of P. australis and B. planiculmis. Our results showed that the leaf area, root biomass, and clonal biomass of P. australis significantly increased, and the leaf area of B. planiculmis significantly decreased under low and medium saline–alkaline concentration treatments, while the plant height, ramet number, and aboveground biomass of P. australis and the root biomass, clonal biomass, and clonal/belowground biomass ratio of B. planiculmis were significantly reduced and the ratio of belowground to aboveground biomass of B. planiculmis significantly increased under high saline–alkaline concentration treatment. The combination of drought conditions with medium and high saline–alkaline treatments significantly reduced leaf area, ramet number, and clonal biomass in both species. The interaction between flooding water level and medium and high saline–alkaline treatments significantly suppressed the plant height, root biomass, and aboveground biomass of both species, with the number of ramets having the greatest contribution. These findings suggest that the effects of water levels and saline–alkaline stress on the functional traits of P. australis and B. planiculmis are species-specific, and the ramet number–plant height–root biomass (RHR) strategy may serve as an adaptive mechanism for wetland clones to environmental changes. This strategy could be useful for predicting plant productivity in saline–alkaline wetlands. Full article

Understanding the relationships between diversity and functional traits in plant communities is essential for elucidating ecosystem functions, forecasting community succession, and informing ecological restoration efforts in arid regions. Although the current research on plant functional traits and diversity has improved our ability to predict ecological functions, there are still many problems, such as how environmental changes affect the relationship between species diversity and plant functional traits, and how these interactions affect plant community functions. We examined the relationships among leaf and fine root functional traits, species diversity, and functional diversity at the community level, along with their environmental interpretations, in a plant community within the desert–oasis transition zone of the Hexi Corridor, where habitats are undergoing significant small-scale changes. During dune succession, plant community composition and diversity exhibited significant variation. Plants are adapted to environmental changes through synergistic combinations of above-ground and below-ground traits. Specifically, plants in fixed dunes adopted a “slow investment” strategy, while those in semi-fixed and mobile dunes employed a “fast investment” approach to resource acquisition. A strong coupling was observed between plant community functional traits and species diversity. Soil phosphorus content and compactness emerged as primary factors influencing differences in plant community functional traits and composition. These soil factors indirectly regulated fine root functional traits and diversity by affecting species diversity, thereby driving community succession. Our study elucidates the “soil—diversity—community functional trait” linkage mechanisms in the successional process of desert plants. This research provides scientific support for the restoring and reconstruction of degraded ecosystems in arid zones. Full article

Nitrogen deposition is a critical driver of plant-soil interactions in forest ecosystems. However, the species-specific coordination of nitrogen uptake and carbon assimilation—traced using ¹⁵N- and ¹³C-labeled compounds—under varying nitrogen forms, depths, and time points remains poorly understood. We conducted a dual-isotope (¹⁵NH₄Cl, K¹⁵NO₃, and Na₂¹³CO₃) labeling experiment in a temperate secondary forest to investigate nutrient uptake and carbon assimilation in three understory species—Carex siderosticta, Maianthemum bifolium, and Oxalis acetosella—across three nitrogen treatments (control, low N, and high N), two soil depths (0–5 cm and 5–15 cm), and two post-labeling time points (24 h and 72 h). We quantified ¹⁵N uptake and ¹³C assimilation in above- and belowground plant tissues, as well as ¹⁵N and ¹³C retention in soils. C. siderosticta exhibited the highest total ¹⁵N uptake (2.2–6.9 μg N m⁻² aboveground; 1.4–4.1 μg N m⁻² belowground) and ¹³C assimilation (58.4–111.2 mg C m⁻² aboveground; 17.6–39.2 mg C m⁻² belowground) under high ammonium at 72 h. High nitrogen input significantly enhanced the coupling between plant biomass and nutrient assimilation (R² > 0.9), and increased ¹⁵N-TN and ¹³C-SOC retention in the surface soil layer (13,200–17,400 μg N kg⁻¹; 30,000–44,000 μg C kg⁻¹). Multifactorial analysis revealed significant interactions among nitrogen treatment, form, depth, and time. These findings demonstrate that ammonium-based enrichment promotes nutrient acquisition and carbon assimilation in responsive species and enhances surface soil C—N retention, highlighting the integrative effects of nitrogen form, species traits, and spatial–temporal dynamics on forest biogeochemistry. Full article