Waterlogging stress is a severe constraint in sugar beet production, particularly in growing seasons with high rainfall. In this study, a greenhouse pot experiment was conducted to compare differences in soil microenvironments between the waterlogging-tolerant cultivar SV1433 (non-waterlogged A1, waterlogged A2) and the sensitive cultivar KUHN1260 (non-waterlogged A3, waterlogged A4) under waterlogging stress.The results showed that under waterlogged treatment, sucrase activity in SV1433 decreased from 46.65 mg/g-1 .24h to 36.25 mg/g-1. 24h. In KUHN1260, sucrase activity decreased from 47.54 mg/g-1.24h to 45.88 mg/g-1 .24h. Co-occurrence network analysis revealed that the rhizosphere microenvironment of the waterlogging-tolerant cultivar was more complex. Specifically, the A3 group had the highest number of edges, with 55.87% being positive correlations. In contrast, 49.15% of the correlations in the A4 group were negative, with a clustering coefficient of 0.505. In conclusion, the impact of waterlogging stress on the sugar beet rhizosphere microenvironment shows significant genotypic differences. The waterlogging-tolerant cultivar plays a positive role in mitigating waterlogging stress by maintaining a relatively stable microbial interaction network and moderate shifts in soil parameters. These findings provide a micro-ecological theoretical foundation for selecting waterlogging-tolerant sugar beet cultivars and optimizing cultivation management.
Cadmium (Cd) contamination in agricultural soils represents a persistent environmental challenge, and elucidating rhizosphere microbial responses to Cd stress is essential for optimizing phytoremediation by hyperaccumulator plants. This study examined the rhizosphere bacterial community associated with Sedum plumbizincicola, a Cd hyperaccumulator, across a Cd gradient (0–50 mg kg−1) in a pot experiment lasting 90 days. Alpha diversity displayed no significant differences among gradients, whereas beta diversity analyses revealed evident Cd-driven shifts in community composition (PERMANOVA, p = 0.028). Taxonomic profiling indicated pronounced community turnover, characterized by decreased relative abundances of SC-I-84 and Ellin6067 and enrichment of Sphingomonas across the Cd gradient. Mantel tests identified Cd concentrations in soil and plant tissues as the primary factors explaining variation in bacterial community structure (p < 0.01). PICRUSt2-based functional prediction indicated that major metabolic categories exhibited relatively consistent abundances across the Cd gradient despite drastic taxonomic turnover. Additional KEGG Level 3 analyses further indicated that predicted functional variation remained comparatively limited despite its significant association with taxonomic restructuring. Soil enzyme activities demonstrated enzyme-specific responses to Cd stress: sucrase activity was stimulated at low Cd levels but inhibited at higher concentrations, whereas urease activity showed limited variation. In addition, Sphingomonas abundance was positively correlated with plant tissue soluble sugar content (p < 0.05), indicating a potential association between plant physiological status and microbial community composition. Overall, these outcomes imply that the phytoremediation capacity of S. plumbizincicola is linked to plant physiological tolerance and Cd-dependent changes in rhizosphere microbial responses.
Copper (Cu) pollution posed potential threats to ecological balance and human health due to its non-degradability and bioaccumulation, which highlighted the necessity of developing efficient remediation strategies. Nowadays, plant growth-promoting rhizobacteria (PGPR)-assisted phytoremediation for soil heavy metals (HM) gradually attracted attention, but its removal efficiency was still limited due to some challenges. Bicarbonates, which participated in the precipitation of soil Cu2+ and regulation of rhizosphere microbial activities, might affect the PGPR-assisted phytoremediation efficiency. Therefore, this study explored the potential roles of NaHCO3 (0.75 g kg−1) in phytoremediation process for Cu-contaminated soil (150 mg kg−1) assisted by the Pseudomonas strain A2 with PGP traits during 30 d. Subsequently, it was demonstrated that under Cu pollution, adding bicarbonates improved the growth status of alfalfas compared to only inoculating strain A2, together with elevated soil pH, lower contents of soil exchangeable Cu (37.05%) and higher proportions of lower mobility forms. Meanwhile, adding bicarbonates further promoted the absorption of soil Cu by alfalfa roots and inhibited its transport to aboveground parts. Moreover, applying bicarbonates could also increase rhizosphere bacterial diversity and the abundance of some phyla (Gemmatimonadota, Myxococcota, and Patescibacteria) that might participate in soil remediation, thus restoring soil enzyme activities and nutrient cycling. In summary, NaHCO3 could improve PGPR-assisted phytoremediation efficiency for Cu-contaminated soil by directly acting on plant growth or enriching functional bacteria, further deepening the understanding of the transformation of soil Cu occurrence forms and restoration for soil ecological balance during the PGPR-assisted phytoremediation process under the influence of bicarbonates.
Defoliation profoundly restructures rhizosphere microbial communities, yet the mechanistic basis of these shifts, particularly their post-recovery trajectories, remains poorly understood. We subjected red clover (Trifolium pratense L.)-timothy (Phleum pratense L.) mixtures to non-defoliated control, moderate, and severe defoliation treatments to investigate how stress intensity shapes rhizosphere bacterial community structure, assembly processes, and network organization following complete aboveground regrowth. While moderate defoliation triggered classic overcompensation with complete aboveground biomass recovery, severe defoliation revealed distinct post-recovery belowground legacies: significant root biomass decline, reduced nitrogen (N) fixation, and fundamental microbial community restructuring. Defoliation shifted rhizosphere communities toward copiotrophic taxa, while decreased C:N ratios in companion grass shoots suggest increased N availability, consistent with N release from legume roots as previously documented. Despite stable alpha diversity, severe defoliation drove pronounced beta diversity shifts and recruited unique taxa absent from control communities. Network analysis revealed contrasting intensity-dependent responses: moderate defoliation caused the greatest structural disruption through loss of interactions and reduced connectivity, while severe defoliation triggered complete network reorganization with increased density but greater structural vulnerability. Lineage-based assembly profiling identified “switcher” bins that transitioned from stochastic drift to dispersal-limited assembly under severe defoliation, indicating emerging spatial constraints, with divergent trajectories within and across phyla revealing niche collapse in some lineages and competitive dominance in others. These findings demonstrate that belowground microbial legacies can still be detected beyond the point of aboveground recovery, revealing a critical temporal decoupling and providing fundamental insight into the ecological rules structuring rhizosphere communities under disturbance.
Root rot disease severely limits the sustainable cultivation of Panax notoginseng, a famous medicinal plant in Asia, but the mechanisms underlying cultivar differences in disease resistance remain unclear. Here, we compared the root rot incidence and rhizosphere soil properties of green-stemmed and purple-stemmed P. notoginseng in a 21-month field experiment. Compared with green-stemmed P. notoginseng, the root rot incidence of purple-stemmed P. notoginseng decreased by 35.07%. While soil physicochemical properties and enzyme activities showed no significant differences (P > 0.05), the purple-stemmed P. notoginseng had higher abundances of potentially beneficial fungi, including Chaetomium, Mortierella, and Rhizophlyctis in the rhizosphere soil; however, the green-stemmed individuals were enriched in potential pathogens such as Plectosphaerella and Ilyonectria (P < 0.05), which was consistent with the results of FUNGuild prediction. The confrontation assays showed that Chaetomium cochliodes and C. globosum, isolated from the rhizosphere soil of purple-stemmed P. notoginseng, exhibited strong biocontrol effects against the key root rot pathogens Fusarium solani and F. oxysporum. Moreover, the fungal community evenness index was 0.55 in the rhizosphere soil of green-stemmed P. notoginseng, which increased to 0.90 in the rhizosphere soil of purple-stemmed P. notoginseng. Phylogenetic community structure and network analyses indicated that the fungal community in the rhizosphere soil of purple-stemmed P. notoginseng exhibited stronger phylogenetic clustering and greater network complexity. Therefore, the rhizosphere soil of purple-stemmed P. notoginseng may harbor a more disease-suppressive fungal community, which is associated with the suppression of root rot disease.
Microbial inoculants based on Bacillus spp. are increasingly used in agriculture; however, their effects on plant-associated fungal communities and the potential influence of bacteria-free carrier media remain poorly understood. In this study, we evaluated the effects of Bacillus siamensis BACIII inoculation and the independent effects of the bacteria-free carrier medium on the root–rhizosphere composite mycobiome of soybean (Glycine max) and sunn hemp (Crotalaria juncea) cultivated under greenhouse conditions. ITS1 metabarcoding generated 9,043,835 high-quality sequences, with rarefaction curves reaching saturation across treatments. In sunn hemp, BACIII inoculation was associated with a more balanced distribution of Ascomycota, Basidiomycota, and Chytridiomycota, whereas soybean communities remained dominated by Ascomycota. Beta diversity analyses revealed significant differences in fungal community composition among treatments in both sunn hemp (Bray–Curtis PERMANOVA: R2 = 0.432, p = 0.001) and soybean (R2 = 0.374, p = 0.001). Functional analyses based on FungalTraits showed treatment-dependent shifts in fungal guild composition, particularly in sunn hemp (PERMANOVA: R2 = 0.815, p = 0.001). Alpha diversity responses were host dependent, with BACIII-treated soybean communities showing the highest mean diversity values, although differences were mainly detected relative to the carrier medium control (Control_II). In sunn hemp, the highest diversity values were observed in Control_II. Differential abundance analyses identified treatment-associated shifts in Rhizoctonia, Fusarium, Aspergillus, and Thelonectria. Ecological assembly analyses indicated that ecological drift was the main inferred structuring process across treatments, while the relative contribution of stochastic and deterministic processes varied between hosts. These results demonstrate that BACIII inoculation and the bacteria-free carrier medium can influence the root–rhizosphere composite mycobiome in a host-dependent manner. This greenhouse study evaluated a single post-inoculation time point and did not quantify BACIII colonization, limiting inference about long-term microbial dynamics. Future studies integrating temporal sampling and field validation are needed to clarify the relative contributions of inoculant and carrier effects under agricultural conditions.
The rhizosphere is a spatially structured chemical interface in which crop roots, microorganisms, and the soil matrix jointly regulate nutrient acquisition, stress adaptation, immunity, and disease development. This critical review narrows its scope to the latest analytical, computational, and experimental approaches used to establish causal chemical communication between crop plants and rhizosphere microbes. Rather than cataloguing all reported exudates and microbial metabolites, the review follows an evidence pathway from signal production and transport to microbial perception, plant feedback, and validation of health- or disease-related outcomes. Particular emphasis is placed on rice, wheat, maize, and horticultural crops, while evidence from Arabidopsis thaliana is used selectively when it provides receptor-, transporter-, or mutant-level mechanisms that can be transferred to crop research. We critically assess untargeted and spatial metabolomics, metagenomics, metatranscriptomics, metaproteomics, single-cell and microfluidic approaches, synthetic microbial communities, genome-scale metabolic modeling, and ecological network inference. The synthesis shows that no single platform can distinguish a nutrient substrate, ecological cue, and biologically effective signal. Robust inference requires coordinated spatial and temporal sampling, source and receiver attribution, perturbation and rescue experiments, and external validation across crop genotypes, soils, management systems, and disease contexts. A crop-focused workflow is proposed to connect molecular measurements with microbiome function and agronomic phenotypes, thereby guiding the development of reproducible inoculants, exudate-informed breeding strategies, and precisely delivered signaling interventions for sustainable plant health management.
Cold temperatures and seasonal freeze-thaw cycles in cold regions are key environmental factors limiting soybean growth, development, and yield improvement. These conditions frequently cause soil structure degradation, inefficient nutrient cycling, and suppressed microbial activity. Single agronomic measures are difficult to achieve systematic improvement.Arbuscular mycorrhizal fungi (AMF) and chitosan, as green regulatory materials, have been individually proven to promote crop growth and optimize rhizosphere microenvironments. However, their synergistic mechanisms in regulating rhizobacterial community structure and network stability, and simultaneously enhancing soil quality and soybean productivity in cold-region systems, remain unclear.Therefore, this study established four treatments: CK (control), FM (inoculation with Funneliformis mosseae alone), Q (chitosan application alone), and FQ (AMF + chitosan). Through cold-region field experiments, we explored their individual and combined effects on soybean growth, soil quality, and rhizosphere bacterial communities.Results showed that FQ significantly optimized soybean growth traits and yield components. The soil quality index (SQI) reached the highest level among all treatments. Soil urease, alkaline phosphatase, and β-glucosidase activities were all significantly enhanced.Microbial community analysis showed that FQ treatment significantly optimized bacterial α-diversity and composition, enriched beneficial stress-resistant groups, strengthened bacterial network properties, and shifted community assembly to stochastic-deterministic synergy dominated by stochastic dispersal.In summary, co-application of AMF and chitosan can synergistically reshape rhizobacterial community structure, enhance interspecific networks, and improve soil quality, thereby promoting the soybean-soil-microbe system in cold regions and offering a theoretical foundation and technical support for green high-yield soybean production and soil health management.
Plants exude carbon-rich compounds into the rhizosphere, which prime microbial activity to oxidize organic carbon and enhance nutrient turnover. Salt marshes are known as key carbon sinks globally, yet it is unclear how patterns of carbon exudation vary along salinity gradients and between vegetation zones that are shifting with accelerated sea level rise. Using a full-factorial microbially-reduced hydroponic experiment, we quantified carbon exudation rates between dominant tidal marsh species (Spartina alterniflora, Phragmites australis, control), salinities (0, 9, 18 ppt), and shade (0, 55%) treatments. In addition, we characterized the root associated microbial populations and evaluated the impact of antibiotic perturbation on microbial activity, carbon exudation rates, and sugar profiles. Carbon exudation rates (μg C hr−1 g root−1) varied among salinity—but not species or shade—treatments, with more carbon accumulating in higher salinity treatments (18 ppt and 9 ppt > 0 ppt). However, root biomass production varied by species, salinity, and shade conditions, demonstrating that biomass production is sensitive to abiotic shifts. Further, root biomass was strongly correlated with carbon exudation rates, indicating that root abundance may be a good predictor of carbon exudation rates. Microbial community structure altered both carbon exudation rates and sugar profiles, and microbial community richness and diversity were altered by the presence of either plant species. Overall, our experimental findings indicate that soil carbon exudation rates could be linked to biomass production in-situ.
Single-rhizome ginseng (SRG) is widely cultivated, whereas rare multi-rhizome ginseng (MRG) remains poorly characterized with limited research on its quality formation. In this study, differential and correlation analyses of tissue-specificity quality indicators and rhizosphere soil properties were performed on SRG and two types of MRG (double- and triple-rhizome ginseng) at different ages. The results demonstrated that MRG exhibited superior performance in agronomic traits (taproot length, root length, fresh weight, and dry weight), tissue-specific chemical constituents (ginsenosides, total flavonoids, total sugar, and soluble protein), and endophytic extracellular enzyme activities (urease, protease, invertase, etc.) compared with SRG. Easily oxidizable organic carbon, macro-aggregates (>2 mm), characteristic phosphorus fractions, as well as β-amylase, α-glucosidase, and laccase were identified as key factors contributing to the divergence of rhizosphere soil physicochemical properties and enzyme activities between SRG and MRG. Correlation analysis revealed that general soil factors including manganese ions, water-soluble ferrous ions, exchangeable ferrous ions, and dissolved organic carbon were closely correlated with the comprehensive quality of both SRG and MRG. Additionally, available potassium, inorganic phosphorus, available boron, alkali-hydrolyzable nitrogen, and available sulfur represented unique soil variables tightly associated with MRG quality. The coupled effects of these macro and trace elements may participate in regulating the morphological development and quality formation of MRG. Collectively, this work clarifies the potential linkage between quality differentiation of SRG/MRG and rhizosphere microenvironment, and provides a theoretical framework for understanding rhizome-architecture-driven quality formation.
Root hairs and arbuscular mycorrhizal fungi (AMF) are two fundamental belowground strategies for nutrient and water acquisition. Root hairs are tubular extensions of root epidermal cells that increase absorptive surface area, while AMF form extensive hyphal networks beyond the rhizosphere. This review synthesizes recent advances on the bidirectional interplay between AMF and root hairs. AMF colonization modulates root hair morphogenesis through the Common Symbiosis Signaling Pathway and hormonal crosstalk involving auxin, strigolactones, and jasmonates. Reciprocally, root hair integrity influences fungal entry and symbiotic efficiency. Spatially, root hairs exploit the immediate rhizosphere (approximately 0.1–1.0 mm from the root surface), whereas AMF hyphae forage in distal soil volumes several centimetres beyond the root, collectively partitioning the soil nutrient pool. Temporally, root hairs provide an early-season uptake capacity before AMF colonization is fully established, while AMF contribute to nutrient acquisition during later growth stages when root senescence reduces hair functionality. Functional complementarity shifts along a collaboration gradient that is dynamically modulated by environmental factors: drought stress enhances AMF-mediated water uptake and root hair maintenance through abscisic acid signaling, salinity impairs root hair elongation while AMF colonization alleviates ionic toxicity, and soil texture determines the relative efficiency of each pathway, with AMF hyphae excelling in coarse-textured soils and root hairs providing critical root-soil contact in compacted substrates. In species with scarce root hairs (e.g., citrus), AMF dependence is heightened. Applications include AMF-based biofertilizers and breeding for root hair traits. Critical knowledge gaps remain in cell-type-specific responses, field stability, and climate-change effects, which must be addressed to translate mechanistic insights into field-scale solutions. Future research should focus on cell-type-specific mechanisms, long-term field studies, and synthetic biology.
Root exudates are key regulators of rhizosphere microbial assembly, yet their influence on pathogen-associated microbial dynamics across contrasting soil types remains incompletely understood. This study investigated how wheat-derived root exudates influence soil microbiomes and affect Rhizoctonia solani AG8 abundance in two contrasting soils with different suppressive capacities. Hydroponically collected root exudates were chemically characterized, exhibiting 930 putatively annotated metabolite features comprising diverse putatively annotated compounds, largely associated with central carbon metabolism and lipid related annotation categories. These exudates were applied at low (1 ppm C) and high (100 ppm C) concentrations under pathogen-challenged conditions. Microbial community responses were assessed using 16S rRNA and ITS amplicon sequencing, and pathogen abundance was quantified by quantitative PCR. The result showed that fungal communities exhibited strong, dose-dependent responses to exudate amendment in suppressive soils, whereas bacterial communities remained comparatively stable across treatments and soil types. High dose exudate application was associated with significantly reduced R. solani AG8 DNA abundance in suppressive soils. In non-suppressive soils, pathogen levels remained broadly similar across treatments under exudate amendment. Although both soil types contained overlapping microbial taxa, exudate-driven shifts in specific microbial taxa were strongly dependent on soil characteristics and treatment conditions. Microbial cooccurrence network showed changes in microbial association patterns, particularly among fungal taxa, following exudate addition These findings suggest that wheat root exudate inputs can act as context-dependent drivers of fungal community assembly and pathogen associated responses, with effect influenced by exudate dose and soil characteristics. This study highlights root exudates as important regulators of rhizosphere microbial interactions and provides a foundation for future mechanistic studies of soil disease suppression.
Crop domestication has significantly altered plant defense traits; however, its impact on the functional structure of plant-associated microbiomes remains poorly understood. These microbiomes are essential for plant growth, nutrient uptake, and defenses against pests and pathogens. The extent to which domestication influences the functional organization of these microbial communities is still unclear. In this study, we assessed the functional traits of microbial isolates from fifteen wild tomato species and cultivated tomato (Solanum lycopersicum) across multiple plant compartments. We evaluated bacterial isolates for plant growth–promoting traits, extracellular enzyme activities, quorum-sensing interference, pathogen inhibition, and the presence of defense-related genes.Functional screening revealed significant differences between the microbiomes of wild and cultivated tomatoes. Microbes from wild tomato hosts exhibited greater defense-related functional capacity, including higher quorum-quenching activity (15.19 vs. 3.0, P = 0.007) and strong inhibition of pathogens such as Xanthomonas vesicatoria (13.82, P = 0.03) and Sclerotium rolfsii (13.54, P = 0.003). In contrast, isolates from cultivated tomatoes did not demonstrate such inhibitory effects. PCR screening showed that cry toxin genes were present only in isolates from wild tomato plants, primarily within the Bacillus cereus species complex, including Bacillus thuringiensis and B. cereus. Correlation network analysis revealed extensive functional connectivity among plant growth-promoting, enzymatic, signaling, and defense traits in wild tomato-associated isolates, whereas isolates from cultivated tomatoes exhibited a simpler trait network. Principal component analysis indicated that microbial functional traits clustered along distinct axes related to nutrient acquisition, enzymatic activity, signaling interference, and pathogen suppression. These findings suggest that crop domestication is associated with alterations in the functional architecture of cultivable tomato-associated microbiomes. Consequently, wild tomato microbiomes represent valuable sources of multifunctional microbes for microbiome-assisted crop improvement and sustainable pest management.
Root exudates serve as a critical pathway for rhizosphere carbon input, yet their response to salinity gradients in inland salt marshes remains unclear. This study investigated Triglochin maritimum across low, moderate, and high salinity zones in the Qinwangchuan salt marsh. We measured root functional traits, root dehydrogenase activity, and root exudation carbon flux to reveal their responses to soil salinity. Results showed that decreasing salinity significantly increased plant height, fine root biomass, specific root length, root dehydrogenase activity, and root exudation rates. root dehydrogenase activity was strongly positively correlated with soil water content (p≤0.01). Exudation rates were closely related to specific root length (p≤0.01), and root exudation carbon flux was significantly positively correlated with fine root biomass (p≤0.01). The water-salinity dynamics in inland salt marsh wetlands influence root architecture, regulate root dehydrogenase activity, and alter root exudation rates and exudate carbon flux. With increasing salinity, salt marsh wetlands exhibit a tendency toward weakened carbon sink function.
This study investigated yield maintenance, root physiological responses, and rhizosphere microbial community variation in two rice cultivars (Oryza sativa L.), the indica-japonica hybrid ‘Jiakeyou 11’ (JKY) and the conventional japonica cultivar ‘Zhehexiang 2’ (ZHX), under nitrogen limitation. JKY maintained grain yield under low N, primarily driven by a large-panicle architecture, robust sink capacity, and consistent grain-filling. Compared to ZHX, JKY exhibited superior panicle dry matter accumulation and highly efficient N remobilization from vegetative organs to panicles. Physiologically, JKY sustained elevated root vitality, soil urease, and N-assimilation enzyme activities, indicating its metabolic processes were minimally constrained by low-N stress. Microbiome analyses revealed that JKY maintained a highly stable core rhizosphere community under reduced N, forming close associations with low-N-adapted taxa such as Pseudolabrys, Gaiella, and Methyloceanibacter. Furthermore, reflecting cultivar-driven differences in microbial community structure, Puia, Ignavibacterium, and Rubrobacter emerged as unique dominant genera in JKY soil, while Lysobacter, Terrabacter, and Methanobacterium dominated ZHX soil. Ultimately, this study uncovers the synergistic dynamics between yield formation, root physiology, and rhizosphere microbial diversity under N restriction, providing a theoretical foundation for reduced-N cultivation in hybrid rice systems.
Fertilization influences crop productivity and soil microbial communities, yet its effects on fungal dynamics across plant developmental stages remain insufficiently resolved. This study examined the impact of organic (cow dung) and inorganic (NPK) fertilization on sorghum rhizosphere fungal communities across vegetative, reproductive transition, and maturity stages. High-throughput ITS sequencing generated 49,403–56,498 reads per sample, yielding 31,761–35,978 high-quality reads and 5487 ASVs after rarefaction (1118–1298 ASVs per sample). Alpha diversity showed clear treatment and stage effects, with NPK supporting higher richness at the vegetative stage (ACE ≈ 507), while cow dung promoted greater diversity and evenness at maturity (Shannon ≈ 4.20), compared with lower diversity in control soils (ACE ≈ 265; Shannon ≈ 3.54). Beta diversity analyses demonstrated significant but generally moderate differences in fungal community composition among fertilization treatments and developmental stages (ANOSIM R = 0.17–0.59, P < 0.05). Community differentiation decreased during the reproductive transition stage, resulting in partial convergence of fungal assemblages before divergence increased again at physiological maturity. Ascomycota dominated across all samples (60–80%), with NPK enriching Eurotiomycetes, Pleosporales, and Hypocreales, whereas cow dung favored Basidiomycota and saprotrophic genera such as Cladosporium, Fusarium, Cercophora, and Podospora. Functional prediction using FUNGuild indicated an increased relative abundance of saprotrophic and symbiotrophic fungal guilds under organic fertilization, whereas the unfertilized control and NPK-treated soils showed relatively higher abundances of pathotrophic guilds. Circos visualization revealed stage-dependent differences in the distribution and relative associations of dominant fungal taxa across fertilization treatments, with organic fertilization supporting a broader representation of dominant fungal taxa, particularly at physiological maturity. Overall, fertilization regime and plant developmental stage were significantly associated with fungal community assembly and succession, with observed patterns corresponding to differences in soil physicochemical properties.
