Plant-soil Interactions Research Articles

Exploring soil-root interactions: A comparative study of wheat species and soil types

Soil-plant interactions of different wheat species (e.g., common, synthetic, durum and wild emmer ancestor) have not been studied yet. Therefore, our study was conducted to examine the interactive effect of 39 treatments including four wheat species (twelve varieties) and three soil types (loamy sand, sandy loam and sandy clay loam) on soil physical and biophysical quality indicators in a greenhouse pot experiment. The rhizosphere data were compared with the no plant (control) soil as well. The results revealed that the rhizosphere soils had a greater soil organic carbon (SOC) storage compared to the no plant soil, with the synthetic wheat species possessing the highest SOC content (order of SOC: synthetic > durum > emmer > common > control). The highest and the lowest SOC values (0.79 and 0.69 kg 100 kg−1) were observed in the rhizosphere of synthetic wheat S88 and common wheat CK varieties, respectively. The SOC showed a positive correlation with root morphological traits such as root volume and root dry weight. Basal soil respiration (BSR) showed significant variation among the four wheat species, and common and emmer ones had the highest BSR values. The maximum and minimum values of BSR (21.9 and 10.9 mg CO2 kg−1 soil day−1) were observed in the rhizosphere of the common species planted in sandy loam soil and in the loamy sand bulk soil (control), respectively. The presence of plant roots significantly increased BSR compared to the control (bulk soil); on average, the BSR in the rhizosphere was 21% greater than the control. Both the wheat species and soil type significantly affected the soil water repellency index (RI) and wettability parameters, but the interactive effects of treatments (i.e., wheat species and soil type) were not significant. The soils in all of the studied treatments were sub-critically or slightly water repellent (i.e., contact angle lower than 90°). The RI values were measured in the order emmer > durum > common > control ≥ synthetic; however, the difference between the synthetic species and bulk soil was not significant. Plant roots increased the soil hydrophobicity by increasing the SOC storage and significant variations in RI among the wheat species indicated that the emmer, durum and common species with greater RI might have better soil physical quality in the rhizosphere. The wheat plants substantially increased water-stable aggregates and decreased water-dispersible clay in the rhizosphere compared to the bulk soil. These findings showed that wheat roots were able to alter the structural stability of the rhizosphere soil. Correlation analysis indicated that soil structural stability was closely related to the SOC, microbial activity, water repellency and root morphological traits. Principal component analysis was used to enhance visualization, identify interrelationships between soil quality indicators and categorize wheat varieties.

Genetic relatedness can alter the strength of plant-soil interactions.

Intraspecific variation may play a key role in shaping the relationships between plants and their interactions with soil microbial communities. The soil microbes of individual plants can generate intraspecific variation in the responsiveness of the plant offspring, yet have been much less studied. To address this need, we explored how the relatedness of seedlings from established clones of Solidago altissima altered the plant-soil interactions of the seedlings. Seedlings of known parentage were generated from a series of 24 clones grown in a common garden. Seedlings from these crosses were inoculated with soils from maternal, paternal, or unrelated clones and their performance compared to sterilized control inocula. We found that soil inocula influenced by S. altissima clones had an overall negative effect on seedling biomass. Furthermore, seedlings inoculated with maternal or paternal soils tended to experience larger negative effects than seedlings inoculated with unrelated soils. However, there was much variation among individual crosses, with not all responding to relatedness. Our data argue that genetic relatedness to the plant from which the soil microbial inoculum was obtained may cause differential impacts on establishing seedlings, encouraging the regeneration of non-kin adjacent to established clones. Such intraspecific variation represents a potentially important source of heterogeneity in plant-soil microbe interactions with implications for maintaining population genetic diversity.

Divergent soil P accrual in ectomycorrhizal and arbuscular mycorrhizal trees: insights from a common garden experiment in subtropical China.

Tree species establish mycorrhizal associations with both ectomycorrhizal (EM) and arbuscular mycorrhizal fungi (AM), which play crucial roles in facilitating plant phosphorus (P) acquisition. However, little attention has been given to the effects of EM and AM species on soil P dynamics and the underlying mechanisms in subtropical forests, where P availability is typically low. To address this knowledge gap, we selected two EM species (Pinus massoniana - PM and Castanopsis carlesii - CC) and two AM species (Cunninghamia lanceolata - Chinese fir, CF and Michelia macclurei - MM) in a common garden established in 2012 in subtropical China. We investigated soil properties (e.g., pH, soil organic carbon, total nitrogen, and dissolved organic nitrogen), soil P fractions, phospholipid fatty acids (PLFAs), enzyme activities, foliar manganese (Mn) concentration, and foliar nutrients and stoichiometry. Our findings revealed that soils hosting EM species had higher levels of resin P, NaHCO3-Pi, extractable Po, total P, and a greater percentage of extractable Po to total P compared to soils with AM species. These results indicate that EM species enhance soil P availability and organic P accumulation in contrast to AM species. Moreover, EM species exhibited higher P return to soil (indicated by higher foliar P concentrations) when compared to AM species, which partly explains higher P accumulation in soils with EM species. Additionally, resin P showed a positive correlation with acid phosphatase (ACP) activity, whereas no correlation was found with foliar Mn concentration, which serves as a proxy for the mobilization of sorbed soil P. Such findings indicate that organic P mineralization has a more substantial impact than inorganic P desorption in influencing P availability in soils hosting both EM and AM species. In summary, our study contributes to a more comprehensive understanding of the effects of mycorrhizal associations on soil P accumulation in subtropical forests and provide valuable insights into plant-soil interactions and their role in P cycling in regions with limited P availability.

Soil microbial communities along elevational gradients in the Madrean Sky Islands.

The Madrean Sky Islands are mountain ranges isolated by a 'desert sea'. This area is a biodiversity hotspot currently threatened by climate change. Here, we studied soil microbial communities along elevational gradients in eight Madrean Sky Islands in southeastern Arizona (USA). Our results showed that while elevational microbial richness gradients were weak and not consistent across different mountains, soil properties strongly influenced microbial community composition (overall composition and the abundance of key functional groups) along elevational gradients. In particular, warming is associated with a higher abundance of soil-borne fungal plant pathogens that concomitantly might facilitate upward elevational shifts of plant species released from negative plant-soil feedbacks. Furthermore, projected warming and drought in the area aggravated by anthropogenic nitrogen deposition on mountain tops (and thus, decreasing nitrogen limitation) can enhance a shift from ectomycorrhizal to arbuscular mycorrhizal fungi. Overall, these results indicate that climate change effects on plant-soil interactions might have profound ecosystem consequences.

Plant–plant and plant–soil interactions under drought and the presence of invasive buffelgrass (Cenchrus ciliaris)

Plant–plant and plant–soil interactions under drought and the presence of invasive buffelgrass (Cenchrus ciliaris)

Numerical Analysis of the Transfer Dynamics of Heavy Metals from Soil to Plant and Application to Contamination of Honey

We analyze a mathematical model of the effects of soil contamination by heavy metals, which is expressed as systems of nonlinear ordinary differential equations (ODEs). The model is based on the symmetry dynamics of heavy metals soil–plant interactions. We aim to study this symmetric process and its long-term behavior, as well as to discuss the role of two crucial parameters, namely the flux of the hydrogen protons to the soil in rainfall events W(t), and the available water for roots p(t). We study the boundedness and positivity of the solution. Further, a parameter identification analysis of the model is presented. Numerical experiments with synthetic and realistic data of honeybee population are discussed.

Can models adequately reflect how long-term nitrogen enrichment alters the forest soil carbon cycle?

Abstract. Changes in the nitrogen (N) status of forest ecosystems can directly and indirectly influence their carbon (C) sequestration potential by altering soil organic matter (SOM) decomposition, soil enzyme activity, and plant–soil interactions. However, model representations of linked C–N cycles and SOM decay are not well validated against experimental data. Here, we use extensive data from the Fernow Experimental Forest long-term whole-watershed N fertilization study to compare the response to N perturbations of two soil models that represent decomposition dynamics differently (first-order decay versus microbially explicit reverse Michaelis–Menten kinetics). These two soil models were coupled to a common vegetation model which provided identical input data. Key responses to N additions measured at the study site included a shift in plant allocation to favor woody biomass over belowground carbon inputs, reductions in soil respiration, accumulation of particulate organic matter (POM), and an increase in soil C:N ratios. The vegetation model did not capture the often-observed shift in plant C allocation with N additions, which resulted in poor predictions of the soil responses. We modified the parameterization of the plant C allocation scheme to favor wood production over fine-root production with N additions, which significantly improved the vegetation and soil respiration responses. Additionally, to elicit an increase in the soil C stocks and C:N ratios with N additions, as observed, we modified the decay rates of the POM in the soil models. With these modifications, both models captured negative soil respiration and positive soil C stock responses in line with observations, but only the microbially explicit model captured an increase in soil C:N. Our results highlight the need for further model development to accurately represent plant–soil interactions, such as rhizosphere priming, and their responses to environmental change.

Challenges and Opportunities in Biofertilizer Commercialization

As eco-friendly alternative to chemical fertilizers, biofertilizers have gained significance in the quest for sustainable farming. While challenges exist, such as regulatory hurdles and technical complexities, the opportunities in this field are substantial. Understanding rhizosphere engineering can enhance biofertilizers' efficiency, ensuring they provide maximum crop benefits. Genetic engineering of bioinoculants offers a pathway to tailor biofertilizers to specific crop needs, potentially increasing their effectiveness. Multi-trait, multi-strain, and multi-nutrient microbial formulations have the potential to revolutionize the biofertilizer market, allowing for customized solutions that address a range of agricultural needs. These innovations are complemented by market dynamics and the integration of nanotechnology, which can further enhance biofertilizer performance and reach. Such opportunities indicate a bright future for biofertilizer commercialization, where sustainable agriculture can benefit from advanced formulations with an improved understanding of soil-plant interactions. Biofertilizers' prospects are promising, offering a more sustainable and environmentally friendly approach to nourishing the world's growing population.

Selective logging impacts on soil microbial communities and functioning in Bornean tropical forest.

Rainforests provide vital ecosystem services that are underpinned by plant-soil interactions. The forests of Borneo are globally important reservoirs of biodiversity and carbon, but a significant proportion of the forest that remains after large-scale agricultural conversion has been extensively modified due to timber harvest. We have limited understanding of how selective logging affects ecosystem functions including biogeochemical cycles driven by soil microbes. In this study, we sampled soil from logging gaps and co-located intact lowland dipterocarp rainforest in Borneo. We characterised soil bacterial and fungal communities and physicochemical properties and determined soil functioning in terms of enzyme activity, nutrient supply rates, and microbial heterotrophic respiration. Soil microbial biomass, alpha diversity, and most soil properties and functions were resistant to logging. However, we found logging significantly shifted soil bacterial and fungal community composition, reduced the abundance of ectomycorrhizal fungi, increased the abundance of arbuscular mycorrhizal fungi, and reduced soil inorganic phosphorous concentration and nitrate supply rate, suggesting some downregulation of nutrient cycling. Within gaps, canopy openness was negatively related to ectomycorrhizal abundance and phosphomonoesterase activity and positively related to ammonium supply rate, suggesting control on soil phosphorus and nitrogen cycles via functional shifts in fungal communities. We found some evidence for reduced soil heterotrophic respiration with greater logging disturbance. Overall, our results demonstrate that while many soil microbial community attributes, soil properties, and functions may be resistant to selective logging, logging can significantly impact the composition and abundance of key soil microbial groups linked to the regulation of vital nutrient and carbon cycles in tropical forests.

Initial microbiome and tree root status structured the soil microbial community discrepancy of the subtropical pine-oak forest in a large urban forest park.

Plant-microbe-soil interactions control over the forest biogeochemical cycling. Adaptive plant-soil interactions can shape specific microbial taxa in determining the ecosystem functioning. Different trees produce heterogeneous soil properties and can alter the composition of soil microbial community, which is relevant to the forest internal succession containing contrasting stand types such as the pine-oak forests. Considering representative microbial community characteristics are recorded in the original soil where they had adapted and resided, we constructed a soil transplant incubation experiment in a series of in situ root-ingrowth cores in a subtropical pine-oak forest, to simulate the vegetational pine-oak replacement under environmental succession. The responsive bacterial and fungal community discrepancies were studied to determine whether and how they would be changed. The pine and oak forest stands had greater heterogeneity in fungi composition than bacteria. Original soil and specific tree root status were the main factors that determined microbial community structure. Internal association network characters and intergroup variations of fungi among soil samples were more affected by original soil, while bacteria were more affected by receiving forest. Specifically, dominant tree roots had strong influence in accelerating the fungi community succession to adapt with the surrounding forest. We concluded that soil microbial responses to forest stand alternation differed between microbiome groups, with fungi from their original forest possessing higher resistance to encounter a new vegetation stand, while the bacteria community have faster resilience. The data would advance our insight into local soil microbial community dynamics during ecosystem succession and be helpful to enlighten forest management.

Evergreen gymnosperm tree abundance drives ground beetle density and community composition in eastern US temperate forests

PurposeSoil invertebrates are abundant and diverse members of forest ecosystems, contributing in large parts to ecosystem functioning. Understanding drivers of soil invertebrate diversity, density, and community composition is critical to inform management practices as forests face rapid changes in land use and climate. Tree community metrics may help predict invertebrate communities due to their large role in shaping microhabitat and soil conditions. Ground beetles are a large family of soil-dwelling invertebrates comprised of multiple functional groups ideal for tying tree communities to invertebrate communities broadly. Methods Here, we evaluated the effects of tree diversity, density, and functional groups on ground beetle (Carabidae) diversity, density, and community composition in four eastern US temperate forest sites in the National Ecological Observatory Network. Results We found little evidence to support our hypothesis that higher tree diversity and density would, respectively, lead to higher diversity and density ground beetle communities. Instead, evergreen tree abundance strongly shaped ground beetle density and community composition. Specifically, evergreen stands contained a lower density of ground beetles than deciduous stands. Similarly, the relative abundance of predatory ground beetles increased as the relative abundance of evergreen trees increased. Conclusions Our results show that the resource environments created by trees with varying leaf habits are a dominant force driving ground beetle community diversity and density patterns and suggest that future research exploring mechanisms driving this pattern could improve our understanding of plant-soil interactions.

Reference sites of threatened riverine Atlantic forest in upper Rio Doce watershed

The most important condition of ecological restoration is the identification of reference ecosystems, which function as a guide for assertive practice with which biological integrity and ecosystem structure and function can be compared. For restoration and conservation projects to be effective in the current scenario of biodiversity and ecosystem services decay worldwide, it is fundamental to understand the soil-plant interactions in each environment. In this study, we evaluated the structure and composition of the flora in 45 plots, equally distributed in three preserved areas (reference ecosystems) of Atlantic Forest in the upper Rio Doce watershed, Southeast Brazil. We also tested whether differences in species composition were influenced by edaphic factors, both in the adult tree and sapling strata. In both tree and sapling strata, Fabaceae was the species-richest family, followed by Myrtaceae, and Lauraceae. The Fabaceae family also showed the highest importance value for both strata. The soils of the riparian forests were highly heterogeneous among the studied sites. Co-inertia analyses indicated a clear edaphic-floristic gradient in both tree (RV = 0.467; p < 0.001) and sapling (RV = 0.478; p < 0.001) strata, with a connection of 46.7% and 47.8% between the edaphic and floristic matrices for trees and saplings, respectively. We identified the groups of tree and sapling strata species that were strongly associated with either nutritionally richer or poorer soils on each studied site. Understanding how ecological and life-history traits of plant species relate with edaphic factors is an important step to provide scientific-based knowledge to support policies for ecosystem recovery and restoration in the stretches of the Rio Doce watershed.

Polluted soil-plant interaction analysis and soil classification based on laser-induced breakdown spectroscopy and machine learning.

A new method is introduced for the swift and precise detection of soil pollution and its effects on crops. Soil quality is essential for human well-being, with heavy metal pollution presenting considerable risks to both the ecological environment and human health. In crops, heavy metal contamination primarily occurs through mediums such as soil and water sources. This study introduces a system combining Laser-Induced Breakdown Spectroscopy (LIBS) with machine learning (ML) to analyze garlic contaminated by soil and the soil used for its cultivation. The simulation conducted in this study focuses on the impact of heavy metal-contaminated soil on garlic. Detection results indicate a significant influence of soil on garlic, resulting in heavy metal accumulation. Further analysis shows that metals from contaminated soil accumulate differently in various garlic plant parts, as per spectral data, underscoring the need for targeted detection methods to assess crop contamination. Conducting LIBS analysis on various soil samples enables the classification of different soil types. This indicates that tracing the origin of contaminated garlic through its residual soil is feasible. These findings imply the feasibility of tracing contaminated garlic's origin through its residual soil.

Grazing weakens the linkages between plants and soil biotic communities in the alpine grassland

Livestock grazing alters the diversity and composition of plants and soil biota in grassland ecosystems. However, whether and how grazing affects plant-soil biota interactions are limited. Here, we performed a field investigation on the Tibetan grasslands to determine the relationships between plant community properties (biomass, diversity and richness) and soil biota (abundance, diversity and composition of bacteria, fungi and nematodes) in the long-term yak grazing and ungrazed plots, and responses of plant-soil biota linkages to grazing in alpine meadows and alpine swampy meadows were compared. The results found that grazing did not cause significant changes in plant community properties but increased the soil water content. Further, grazing weakened plant-soil microbes/nematode relationships in alpine meadows. The bacterial and fungal abundances were correlated with plant belowground biomass and Simpson index in the ungrazed plots of alpine meadows, while the correlation was not significant under grazing. Bacterial composition was correlated with plant richness only in the ungrazed meadows. Plant-soil nematode linkages were more sensitive to grazing than plant-microbes linkages. Grazing decoupled the relationships between the abundances of nematode trophic groups and plant aboveground biomass, richness and Simpson index in alpine meadows, while the decoupling phenomenon is less evident in alpine swampy meadows. The SEM results indicate that grazing altered the plant above- and belowground biomass to affect the soil nematode community, while influenced soil microbes only through alterations of plant belowground biomass. The findings highlight the importance of grazing in influencing the interactions between aboveground plant communities and soil biological communities in Tibetan grasslands.

A trait-based framework linking the soil metabolome to plant-soil feedbacks.

By modifying the biotic and abiotic properties of the soil, plants create soil legacies that can affect vegetation dynamics through plant-soil feedbacks (PSF). PSF are generally attributed to reciprocal effects of plants and soil biota, but these interactions can also drive changes in the identity, diversity and abundance of soil metabolites, leading to more or less persistent soil chemical legacies whose role in mediating PSF has rarely been considered. These chemical legacies may interact with microbial or nutrient legacies to affect species coexistence. Given the ecological importance of chemical interactions between plants and other organisms, a better understanding of soil chemical legacies is needed in community ecology. In this Viewpoint, we aim to: highlight the importance of belowground chemical interactions for PSF; define and integrate soil chemical legacies into PSF research by clarifying how the soil metabolome can contribute to PSF; discuss how functional traits can help predict these plant-soil interactions; propose an experimental approach to quantify plant responses to the soil solution metabolome; and describe a testable framework relying on root economics and seed dispersal traits to predict how plant species affect the soil metabolome and how they could respond to soil chemical legacies.

Unveiling the soil physicochemical dynamics of bare soils in Southeast Kazakhstan: A comprehensive study in the Akdala Massif

This study addresses desertification in Kazakhstan's Akdala region, aiming to propose sustainable solutions by examining the effects of various plants on soil properties and nutrient dynamics. Desertification poses a threat to land productivity in arid areas, and this research aims to determine its impact on soil and identify plants for mitigation. Field experiments over three years in the Akdala region utilized crops such as rice, corn, soybean, sudan grass, and sorghum to assess their influence on key soil parameters. Results revealed diverse effects on soil bulk density, agronomically valuable aggregates, water-stable aggregates, labile and total organic carbon, easily hydrolyzable nitrogen, nitrate, available phosphorus, and exchangeable potassium. While no significant differences in bulk density were observed among crops, variations in surface and subsurface soil layers emphasized the importance of depth-specific considerations. Sorghum stood out as a particularly influential crop, significantly increasing labile and total organic carbon levels, highlighting its potential role in enhancing soil quality. The experiments were conducted on the fields of "Birlik" LLP in the Balkhash district of the Almaty region from 2015 to 2017. The chosen crops, each with distinct characteristics, provided a comprehensive understanding of their impact on soil dynamics. Advanced techniques for soil sampling and analyses ensured accurate measurements of various soil parameters. The study site's sharply continental climate, marked by temperature variations, snowy winters, and hot, dry summers, added complexity to the investigation due to its influence on plant growth and soil interactions. In conclusion, this comprehensive study offers valuable insights into the intricate relationships between different crops and soil parameters for combating desertification. The findings contribute significantly to the development of sustainable soil management practices, providing a foundation for identifying suitable crops for soil improvement in arid regions. By understanding how different plants impact soil properties, this research supports informed decision-making in agricultural practices, promoting the long-term sustainability of farming in regions vulnerable to desertification.

Soil water components control plant water uptake along a subalpine elevation gradient on the Eastern Qinghai-Tibet Plateau

Soil water is crucial for maintaining forest health by providing plants with a dependable water source. However, the understanding of the impact of soil moisture on plant water uptake, particularly in conditions of excess soil water, is limited. In this study, we investigated root water uptake strategies of dominant species along an elevational gradient in the subalpine region of the eastern Qinghai–Tibet Plateau. Our results demonstrated divergent relationships between soil moisture and water uptake fractions in the shallow soil layer, where moisture generally exceeds field capacity (θfc) during the growing season, and in the deep soil layer, showing negative and positive associations, respectively. This disparity is linked to soil water components: when plants mainly used shallow soil water, the relative proportion of plant–available water (the part of water between wilting coefficient and θfc) in the shallow soil was smaller compared to instances where plants mainly used deep soil water. Conversely, the pattern for gravity water was the opposite. This phenomenon is attributed to precipitation replenishing shallow soil with gravity water and deep soil with plant–available water, leading to poor aeration in the shallow soil and an abundance of plant–available water in the deep soil, and plants tended to shift to deep soil water as a result. Furthermore, the decrease in the relative proportion of plant–available water in the shallow soil along the elevational gradient results in plants in the lowest-altitude broadleaf forest obtaining more shallow soil water and less deep soil water, which can also enhance our understanding of how soil moisture components influence plant water–use strategies. Additionally, no hydrological niche segregation was observed among species in this humid environment. These results can improve our comprehension of soil–plant interactions in subalpine areas.

Unraveling plant adaptation to nitrogen limitation from enzyme stoichiometry aspect in Karst soils: a case study of Rhododendron Pudingense

Enzyme stoichiometry can reflect the resource limitation of soil microbial metabolism, and research on the relationships between plants and resource limitation in Karst Microhabitats is scarcely investigated. To clarify the extracellular enzyme stoichiometry characteristics in soil across different karst microhabitats and how the Rhododendron pudingense adapts to nutrient restrictions, plot investigation experiments were set up in Zhenning County, Qinglong County, and Wangmo County of Guizhou Province which included total three karst microhabitats, i.e., soil surface (SS), rock gully (RG), and rock surface (RS), by analyzing he rhizosphere soil nutrient, extracellular enzyme activity, and nutrient content of R. pudingense. The findings indicated that all karst microenvironments experienced varying levels of nitrogen (N) limitation, with the order of N limitation being as follows: SS > RG > RS. Notably, there were significant discrepancies in N content among different plant organs (p< 0.05), with the sequence of N content as follows: leaf > stem > root. However, no significant differences were observed in nutrient content within the same organ across different microenvironments (p > 0.05). A noteworthy discovery was the significant allometric growth relationship between C-P in various organs (p< 0.05), while roots and stems exhibited a significant allometric growth relationship between N-P (p< 0.05). The study highlighted the substantial impact of Total Nitrogen (TN) and N-acquiring enzymes (NAE) on nutrient allocation within the components of R. pudingense. Overall, the research demonstrated that N was the primary limiting factor in the study area’s soil, and R. pudingense’s nutrient allocation strategy was closely associated with N limitations in the karst microenvironment. Specifically, the plant prioritized allocating its limited N resources to its leaves, ensuring its survival. This investigation provided valuable insights into how plants adapt to nutrient restrictions and offered a deeper understanding of soil-plant interactions in karst ecosystems.

Effects of polyethylene microplastics and heavy metals on soil-plant microbial dynamics

Polyethylene (PE) microplastics are emerging pollutants that pose a significant threat to the environment and human health. However, little is known about the effects of PEs on soil‒plant interactions, especially in heavy metal (HM)-contaminated soil. In this study, the effects of PE on rhizosphere soil enzyme activities, microbial interactions and nutrient cycling processes were analyzed from ecological network and functional gene perspectives for the first time. The results indicated that PE-MP addition significantly reduced the biomass of Bidens pilosa L. In addition, the partial increase in carbon, nitrogen, and phosphorus enzyme activities suggested that the effects of PE as a carbon source on microbial functions in HM-contaminated soil should not be ignored. The average path length of bacterial network nodes was found to be higher than that of fungal network nodes, demonstrating that the bacterial ecological network in PE-MP and HM cocontaminated environments has good buffering capacity against changes in external environmental conditions. Furthermore, structural equation modeling demonstrated that particle size and dosage affect soil nutrient cycling processes and that cycling processes are acutely aware of changes in any factor, such as soil moisture, soil pH and soil nitrogen nutrients. Hence, PE-MP addition in HM-contaminated soil has the potential to alter soil ecological functions and nutrient cycles.

Plant diversity and soil legacy independently affect the plant metabolome and induced responses following herbivory.

Plant and soil biodiversity can have significant effects on herbivore resistance mediated by plant metabolites. Here, we disentangled the independent effects of plant diversity and soil legacy on constitutive and herbivore-induced plant metabolomes of three plant species in two complementary microcosm experiments. First, we grew plants in sterile soil with three different plant diversity levels. Second, single plant species were grown on soil with different plant diversity-induced soil legacies. We infested a subset of all plants with Spodoptera exigua larvae, a generalist leaf-chewing herbivore, and assessed foliar and root metabolomes. Neither plant diversity nor soil legacy had significant effects on overall foliar, root, or herbivore-induced metabolome composition. Herbivore-induced metabolomes, however, differed from those of control plants. We detected 139 significantly regulated metabolites by comparing plants grown in monocultures with conspecifics growing in plant or soil legacy mixtures. Moreover, plant-plant and plant-soil interactions regulated 141 metabolites in herbivore-induced plants. Taken together, plant diversity and soil legacy independently alter the concentration and induction of plant metabolites, thus affecting the plant's defensive capability. This is a first step toward disentangling plant and soil biodiversity effects on herbivore resistance, thereby improving our understanding of the mechanisms that govern ecosystem functioning.