Soil microbial metabolic strategies and the imbalance between available phosphorus and nitrogen controls the root exudate-induced priming effect by grassland tumbleweed (Cleistogenes squarrosa and Saposhnikovia divaricata) root exudates

Advancement in bioremediation of heavy metals in sustainable way: A critical evaluation on current findings and future prospects.

Exudation is crucial for carbon and nutrient cycling in forests. However, the underlying mechanism controlling exudation in mature trees, especially its dependence on mycorrhizal type, remains unknown. Based on the control of carbon acquisition by roots, we propose an updated 'push-trade-off-pull' framework for exudation. We investigated three controlling categories, that is, nonstructural carbohydrates (NSCs) in branches and roots, root functional traits, and soil nutrients, as proxies for 'push', 'trade-off', and 'pull', respectively, over exudation for trees colonized by arbuscular mycorrhizal (AM) or ectomycorrhizal (ECM) fungi in subtropical forests of China. The NSCs, root traits, and soil nutrients together controlled exudation of trees, particularly distinguishing AM from ECM species. Soil nutrients dominantly impacted the exudation of AM species (47%), that is, increased exudation linked with decreased soil nutrients, supporting the 'pull' effect. However, the NSCs mainly mediated that of ECM species (56%), that is, enhanced exudation associated with declined NSCs, which rejects the 'push' effect. For the 'trade-off', greater exudation was correlated with greater root branching for AM and with lower root tissue density for ECM species. Our findings highlight the mycorrhizal symbiosis-dependent mechanism of exuded carbon that provides a new perspective for understanding exudate-mediated belowground carbon cycling in forests.

Increased root growth to access greater soil mineral nitrogen resources, and increased root exudation to stimulate microbial mineralisation of soil organic nitrogen, are widely observed plant acclimations to nitrogen limitation. However, the quantitative contribution of these belowground acclimations to whole plant growth and ecosystem productivity remains largely elusive. Here, we present a novel heuristic optimality-based eco-evolutionary nitrogen foraging model in which plants dynamically regulate carbon partitioning between root growth and exudation to maximise their aboveground growth. Our simulations indicated that the dynamic availability of soil mineral and organic nitrogen, as well as plant nitrogen demand and nitrogen uptake capacity, shape optimal carbon partitioning between root growth and exudation. The simulated carbon allocation patterns aligned with empirical studies on belowground plant responses to varying nitrogen resources in soil. These findings demonstrated the potential and versatility of our model to capture the quantitative importance of root and whole plant physiological acclimations for plant growth and productivity under fluctuating soil nitrogen availability. Our optimality-based approach represents a paradigmatic change in modelling plant nitrogen foraging, which is essential to generate hypotheses on optimal plant acclimations in future soil environments characterised by more erratic nitrogen availability.

Species mixtures and arbuscular mycorrhizae synergistically enhance the belowground benefits in perennial cover crops.

Negative plant–soil feedback (NPSF) drives yield decline in monocropping systems, yet how intraspecific competition modulates NPSF across planting densities remains unclear. We conducted a two-stage plant–soil feedback experiment using five crops (Triticum aestivum L., Zea mays L., Solanum lycopersicum L., Cucumis sativus L., and Panax notoginseng (Burkill) F.H. Chen) with contrasting NPSF intensities under four planting densities (30 × 30 to 8 × 8 cm). Crops with stronger NPSF (P. notoginseng) showed pronounced density-dependent biomass reductions, whereas those with moderate (S. lycopersicum, C. sativus) or low (Z. mays, T. aestivum) NPSF were largely density-insensitive. Given its sensitivity, P. notoginseng was used to explore mechanisms. High-density planting (8 × 8 cm) intensified NPSF, reducing seedling survival by 88.54% and biomass by 56.08% compared with low-density controls (30 × 30 cm). Microbiome profiling showed enrichment of pathogenic Fusarium spp. and depletion of beneficial Humicola spp. under high density. Metabolomic analysis identified linoleic acid and oleamide as key root exudates upregulated under high-density stress, which selectively stimulated Fusarium growth as preferred carbon sources. Collectively, these results reveal a density-dependent feedback in which intensified competition reshapes root exudation, promotes pathogen proliferation, and suppresses beneficial taxa, thereby amplifying NPSF. This provides mechanistic insights into microbially mediated NPSF under density stress and highlights the importance of optimizing planting density to sustain crop productivity.

Nanoparticle-rhizosphere crosstalk: Insights into transformation, microbial interaction, plant uptake and translocation.

Root exudation is a key component of plant-rhizosphere interactome. It is increasingly evident that root exudates influence rhizospheric microbial communities and in turn can benefit plants through improved resource allocation. However, how suboptimal nutrient availability relates to control of root exudation is poorly understood. This study explores effects of calcium and nitrogen availability on barley (Hordeum vulgare L.) root architecture and metabolism with focus on metabolite exudation. Upon depletion of NO3 - from the medium (-N), both sugar and amino acid exudation dropped rapidly within 6 h, but this fast effect was absent for amino acids if also Ca2+ was omitted from the medium (-Ca/-N). In contrast, Ca2+ depletion alone (-Ca) led to a fourfold higher amino acid exudation. Further, a modulatory role for Ca2+ was evident, as the exudation varied in Ca2+-channel inhibitor concentration- and treatment time-dependent manner. Among the 51 detected exuded metabolites, N-deprivation increased the release of specific sugars, i.e. sucrose, fructose, and cellobiose (1.6 to 8-fold), with potential roles as chemoattractants. This pattern is reflected in the increased C/N ratio in -N-exudates. The results show a predominance of nitrogen availability and a modulatory role of Ca2+ in tight regulation of root exudation in dependence of NO3 - availability and metabolic state.

Selenium (Se) orchestrates a multilevel endogenous defense network in crops against cadmium (Cd) toxicity. This network operates from rhizosphere immobilization (e.g., Cd-Se complexes, microbiome interactions, iron plaque, and root exudates) and subcellular sequestration via transporter regulation (e.g., OsNramp5, OsHMA3) to antioxidant enhancement and selenoprotein activation. Critically, Se acts as a signaling initiator, engaging pathways (e.g., GATA3-COMT1-melatonin) to systemically reprogram stress responses. This review highlights that Se's antagonistic efficacy is form-, dose-, and genotype-dependent, providing a mechanistic basis for precision agronomic strategies. Future efforts must bridge laboratory findings to field applications by elucidating molecular switches and developing integrated predictive technologies.

Measuring mangrove root exudation with sealed cuvettes

Spatial heterogeneity of soil phosphorus (P) severely constrains maize productivity, yet the regulatory mechanisms underlying plant adaptation to heterogeneous P supply remain poorly understood. This study reveals the distinct roles of the transcription factors ZmPHR1 and ZmPHR2 in mediating metabolic and rhizosphere microbial responses to heterogeneous P supply in maize (Zea mays L.). Using split-root systems combined with multi-tissue metabolomics and microbiome analysis, we show that mutation of ZmPHR2 severely impaired shoot development, photosynthetic efficiency and systemic P allocation. In contrast, ZmPHR1 mainly influenced root morphological plasticity. Loss of ZmPHR2 led to widespread repression of leaf metabolites, including organic acids and glutathione, and disrupted key pathways such as alanine, aspartate and glutamate metabolism. In root exudates, sphingolipid and histidine metabolism were critical for asymmetric root proliferation. Both mutations abolished differential root growth in P-rich patches and altered bacterial and fungal community composition and network structure. Our findings decipher a ZmPHR1/2-mediated adaptive framework integrating metabolic reprogramming and microbiome assembly, providing a mechanistic basis for breeding P-efficient maize suited to heterogeneous soils.

The rice rhizosphere is a hot spot for nitrogen fixation using carbon sources from root exudates. We herein investigated the intensity of the nitrogen-fixing ability of each diazotroph interacting with other bacteria within the rhizosphere microbiota. We established the Test tube Chemostat replicating Rice Rhizosphere (TCRR) based on four characteristics of the rice rhizosphere: root exudates, percolation, radial oxygen loss, and soil. The TCRR flora constructed by culturing paddy soil using TCRR showed the pH and high nitrogen-fixing ability of the rice rhizosphere. Twenty-five species of diazotrophs from the TCRR flora were categorized into two types: strains producing acetate and ethanol and strains utilizing them. A co-culture of both types resulted in high nitrogen fixation mostly through the acetate interaction. High nitrogen fixation by the TCRR flora was further increased by an inoculation of both Klebsiella pasteurii NG13 and Azospirillum lipoferum FS. These results provide novel insights to develop biofertilizers.

Arbuscular mycorrhizal fungi (AMF) are key drivers of plant growth and nutrition, shaping the relationship between plant diversity and ecosystem productivity. In agroecosystems, AMF generally benefit crops but often have neutral or even negative effects on weeds, yet the mechanisms underlying these contrasting interactions remain poorly understood. In this Viewpoint, we propose a plant community-level framework to investigate interactions between multiple crop and weed species and diverse AMF taxa, focusing on chemically mediated communication via root exudates, particularly flavonoids (FLVs) and strigolactones (SLs). These compounds can act as 'cry for help' signals that recruit beneficial soil microorganisms to alleviate environmental stress. We found that their composition varies widely among plant families, with crops typically producing more diverse and functionally distinctive FLV profiles than weeds. Similar patterns, though less documented, appear for SLs. Different FLV subclasses elicit contrasting AMF responses, influencing spore germination, hyphal growth, and root colonization. Notably, FLVs with stronger positive effects on AMF are more common in crops, whereas those with neutral effects tend to dominate in weeds. Our results are consistent with the idea that such molecular cues may shape AMF recruitment and could potentially feed back into plant community dynamics, although this hypothesis should be explicitly tested.

Cotton damping-off caused by Rhizoctonia solani is the main limiting factor in cotton production, and it is very important to develop effective biological control methods. However, the mechanism by which biostimulants enhance crop disease resistance by recruiting beneficial rhizosphere microorganisms is unclear. Here, we found that after root irrigation of cotton seedlings with PFP1-1, the root soil microbial community structure changed significantly, and the species richness of bacteria and fungi improved. LEfSe analysis confirmed that PFP1-1 could effectively recruit beneficial Bacillus, which was verified by isolation experiments. On this basis, a synthetic microbial community SCII containing the main target Bacillus recruited by PFP1-1 was constructed and configured according to its abundance ratio. Synergistic disease resistance analysis showed that SCII significantly increased the expression levels of resistance genes induced by the jasmonic acid pathway, thereby enhancing the disease resistance of cotton. In addition, chemotaxis experiments confirmed that the PFP1-1 polysaccharide itself and its induced cotton root exudates (such as DL-malic acid and Rosmarinic acid) exhibited significant chemotaxis toward the target Bacillus, indicating the mechanism by which PFP1-1 recruits beneficial bacteria. This study elucidates the protective effect and mechanism of polysaccharide PFP1-1 in cotton, focusing on its ability to recruit beneficial bacteria to enhance crop disease resistance.

The mechanisms of interaction between alfalfa root exudates and rhizosphere bacterial communities for adaptation to salt stress

Drought stress and inefficient resource utilization present considerable obstacles to cotton production. The utilization of Bacillus subtilis signifies a prospective remedy to these challenges. Nevertheless, the precise regulatory systems governing its effects have yet to be identified. This research examined the impact of Bacillus subtilis on cotton output under varying drought stress situations. The experiment utilized cotton as the subject, incorporating two application levels of Bacillus subtilis (0 kg/hm and 45 kg/hm) and two drought stress levels (H, indicating conventional irrigation at 350 mm; L, indicating 80% of conventional irrigation at 280 mm). Each treatment was duplicated thrice. The research assessed the impact of various treatments on dry matter accumulation, photosynthesis, root shape, microbial biomarkers, and root exudates. The findings indicated that the utilization of Bacillus subtilis mitigated the adverse effects of drought stress. In comparison to the control, cotton dry matter mass exhibited a growth of 4.38%–15.24%, the photosynthetic rate rose by 3.47%–11.94%, the transpiration rate augmented by 1.91%–7.53%, stomatal conductance enhanced by 4.54%–8.85%, and intercellular CO 2 concentration elevated by 2.43%–4.32%. Moreover, enhancements in soil root morphology indicators resulted in an 8.94%–9.28% increase in cotton output. Structural equation modeling demonstrated that Bacillus subtilis modulates soil microbial populations, subsequently influencing biomarkers and root exudates. These factors collectively affect photosynthetic characteristics and root shape, improving stomatal conductance and elevating photosynthetic rates. This enhances dry matter buildup and optimizes root architecture, hence enabling the movement of water and nutrients. Consequently, cotton plants can amass greater photosynthetic products, resulting in enhanced dry matter accumulation and elevated yield. The findings suggest that Bacillus subtilis increases productivity during drought stress, offering insights for optimizing cotton production and enhancing yield in arid areas. • Bacillus subtilis improved cotton drought tolerance and increased yield by 8.9–9.3%. • Bacillus subtilis reshaped the rhizosphere microbiome and enriched biomarkers related to nutrient cycling. • Bacillus subtilis altered root exudates, increasing flavonoids and gossypol associated with stress adaptation. • Microbiota and root exudates jointly enhanced cotton physiology and yield under drought.

Priming effects (PE) on soil organic matter (SOM) mineralization depend strongly on the type of carbon substrates added. It is crucial to understand the PE induced by various carbon substrates for predicting SOM dynamics and soil-atmosphere carbon feedback. We conducted a meta-analysis of 8015 observations from 283 articles to evaluate how carbon substrates (plant residues, root exudates, biochar, and degradable microplastics) regulate the mineralization of SOM through PE. Results demonstrated that all these types of carbon substrates increased SOM mineralization, which induced a positive PE. Plant residues induced the highest average PE, followed by root exudates, biochar, and degradable microplastics. Compared to soils without carbon substrate inputs, the rate of SOM mineralization increased by 113% in soil with cellulose-rich non-woody residues, whereas it increased by only 25% in soil with lignin-rich woody residues. The mineralization of SOM increased by organic acids (151%) was greatest in root exudates, followed by monosaccharides (60%) and polysaccharides (12%). The strong mineralization induced by organic acids was probably related to the release of more mineral nutrients by reducing soil pH. The PE on SOM mineralization by woody biochar with high aromatic carbon content (48%) was greater than that of non-woody biochar with high alkyl carbon content (43%). Microplastics with rapidly degradable polyhydroxyalkanoates induced more SOM mineralization (258%) than polybutylene succinate (61%) and polybutylene adipate-co-terephthalate (21%). The SOM priming was positively correlated with soil clay and incubation moisture, and negatively correlated with soil organic carbon, total nitrogen, soil C:N ratio, dissolved organic carbon, microbial biomass carbon, carbon input rate, incubation temperature, and soil depth. These results show that the positive PE is ubiquitous in soil ecosystems; its magnitude is linked intrinsically to the physicochemical characteristics and source of exogenous carbon substrate.

Summary statement In this brief communication, we examined the effects of 4‐year experimental warming on plant species‐specific root exudation dynamics and their associated rhizosphere microbial communities in a temperate grassland ecosystem in Inner Mongolia, China. Our results revealed that Artemisia scoparia exhibited greater sensitivity in carbon and nitrogen exudation rates compared to Stipa krylovii . Furthermore, we identified species‐specific interactions between root exudates and rhizosphere microbiomes: S. krylovii primarily established stronger associations with fungal communities, whereas A. scoparia showed tighter linkages with bacterial communities. These findings underscore the need for future research to investigate how global warming may differently affect above‐ and belowground processes across plant functional groups in grassland ecosystems, particularly with respect to plant‐microbe‐soil feedback mechanisms. These findings suggest that the rhizosphere of different plants recruits different microbial groups to cope with climate warming. These species‐specific compensatory mechanisms could have important implications for nutrient cycling dynamics and ecosystem stability in grasslands under future climate warming.

Plant microbial fuel cells: A self-sustaining bioelectrochemical technology addressing sustainable development goals (SDGs) through bioelectricity production.

Effects of habitat fragmentation on multiple ecosystem functions in urban remnant forests