Soil Feedback Research Articles

Between‐ versus within‐species variation in plant–soil feedback relates to different functional traits, but exudate variability is involved at both scales

Abstract Plant–soil feedback—feedback from plant‐induced changes in soil properties to plant fitness—is increasingly shown to drive the maintenance of local plant diversity at both interspecific and intraspecific levels. A robust understanding of the relationships between plant–soil feedback and functional plant traits, which would improve our ability to generalize plant–soil feedback results beyond specific study systems, is, however, still lacking. This is especially true at the intraspecific plant level. We assessed the relationship between plant–soil feedback and several functional traits in 13 co‐occurring grassland species, including 20 genotypes of the dominant grass, Festuca rubra. The traits encompassed various aspects of growth, root properties and root exudate variability. Combining these traits into principal gradients of functional trait variation, we also tested the potential for the conservation and collaboration gradients to explain variation in PSF. Between‐species plant–soil feedback variation was explained by differences in biomass production and exudate composition, as well as contrasting strategies along the collaboration gradient. Within‐species plant–soil feedback variation—that is between Festuca rubra genotypes—was associated with exudate variability, especially contrasting amounts of exuded phenols. Several traits had a significant effect on plant–soil feedback only via their interaction with exudate composition. Overall, PSF was associated with different traits at between‐species versus within‐species levels. Root exudate variability was, however, involved at both diversity levels. Our results put forth the role of root exudation patterns as an important driver of variation in plant–soil feedback. Better integration between research on plant–soil feedback and on root exudation would therefore improve our understanding of the processes—both ecological and evolutionary—supporting the maintenance of plant diversity within grassland communities. Read the free Plain Language Summary for this article on the Journal blog.

Advances in Plant–Soil Feedback Driven by Root Exudates in Forest Ecosystems

Plant–soil feedback (PSF) was initially developed in the field of agricultural practices. In recent years, PSF has been extended to various ecosystems. Root exudates, essential for the exchange of materials, energy, and information at the plant–soil interface, significantly influence PSF. However, how PSF is driven by root secretions and the role of these secretions in different PSF pathways still needs to be further explored, particularly in forest ecosystems. Soil nutrients, microbial communities, and nematodes are important research topics in the process of PSF driven by root exudates. Investigating these aspects driven by root exudates provides valuable insights into the complex interactions both above ground and below the surface. This research can offer theoretical support and guidance for building stable, healthy, and sustainable forest ecosystems in the future.

Fire effects on soil biota alter the strength and direction of plant-soil feedbacks between Schizachyrium scoparium (Michx.) Nash and Rudbeckia hirta L

Abstract Background and aims Plant soil feedbacks (PSF) are reciprocal mechanisms through which interactions between plants and soil biota and affect future plant growth. When scaled up to the community level, PSFs are important determinants of above- and belowground community dynamics that influence long-term successional trajectories. Despite over three decades of ecological PSF research, we have a poor understanding of how common environmental processes like fire influence the strength and direction of PSFs. The aim of this study was to evaluate fire effects on PSFs between two common grassland species: Schizachyrium scoparium and Rudbeckia hirta. Methods In this work we evaluated how fire effects on S. scoparium and R. hirta associated soil biota influenced feedbacks on plant growth using a two phase experiment. We tested this by first growing S. scoparium and R. hirta with the same soil inocula, and then simulating low intensity, grassland fires in a controlled greenhouse pot experiment (soil training). We then evaluated plant growth responses to burned and unburned inter- and intraspecific soil biota treatments (response phase). Results Fire effects on inocula neutralized negative feedbacks in S. scoparium, and caused negative feedbacks in R. hirta. This shows that environmental disturbance like fire can alter the strength and direction of PSFs in ways that modify plant growth and potentially influence plant fuel loads and community dynamics. Conclusion That fire can alter the strength and direction of PSFs on plant growth suggests that fire effects on soil related processes may influence plant community dynamics and fire-fuel dynamics in fire recurrent grassland ecosystems. Further, this study shows that fire effects on PSFs vary between plant species.

Plant–mycorrhizal associations may explain the latitudinal gradient of plant community assembly

Biogeographical variation in community assembly processes forms the basis of the latitudinal gradient of biodiversity by driving β‐diversity. Classical studies on community assembly predict environmental filtering affecting β‐diversity more strongly at higher latitudes, where productivity is lower and abiotic stress is stronger. Contrary to this prediction, recent evidence indicates that plant community composition at higher latitudes exhibits more spatially clustered distributions independently of background environments, suggesting the importance of spatial processes, such as priority effects. In this study, we propose a hypothesis that resolves this paradox by considering plant–soil feedback and biogeographic variations in the dominant mycorrhizal type: we predict that the increasing prevalence of ectomycorrhizal (EcM) trees with latitude contributes to the spatially clustered distribution of plants, as EcM trees tend to exhibit positive plant–soil feedback. We analyzed a large‐scale standardized dataset of Japanese forests covering a latitudinal gradient of >10° and found that 1) the proportion of EcM trees was higher at higher latitudes, and 2) EcM tree‐rich communities exhibited more spatially clustered distributions likely due to positive plant–soil feedback. Consequently, 3) tree species composition at higher latitudes was better explained by spatial variables suggesting the importance of priority effects. Consistent with the predictions of the plant–soil feedback theory, these patterns were more pronounced in understory than in canopy communities. Taken together, our results lend support to our hypothesis that biogeographic variation in tree community assembly patterns is defined by mycorrhizal types and plant–soil feedback, thereby resolving a paradox in the latitudinal gradient of plant community assembly. Our work highlights that plant mycorrhizal type underlies the determinants of β‐diversity which is a critical component of the latitudinal gradient of diversity.

Forest tree community ecology and plant–soil feedback: Theory and evidence

AbstractMounting evidence suggests that reciprocal interactions between plants and the soil microbiota can be a primary force that generates key macroscopic patterns of plant communities (coexistence, dominance, and succession) in forest ecosystems. The aim of this article is to review empirical and theoretical perspectives of plant–soil feedback research in the context of forest community ecology. I first use a simple theoretical model to get insights into an array of the dynamics generated by plant–soil feedback: negative plant–soil feedback maintains plant species diversity and reduces plant growth, while positive plant–soil feedback drives plant growth of certain species and hence their dominance. I then describe how ecologists have unveiled the enormously complex plant‐microbiota interaction (i.e., the soil conditioning experiment) and review the linkage of plant–soil feedback with three key plant community patterns: (i) dominance, (ii) spatial structure and (iii) succession. I highlight one belowground plant trait (mycorrhizal type) that can mediate these linkages: arbuscular mycorrhizal species tend to exhibit negative plant–soil feedback while ectomycorrhizal species tend to exhibit positive plant–soil feedback. Although mycorrhizal plant–soil feedback potentially explains the patterns of tree diversity from local to global scales, many questions remain. Future studies should expand plant–soil feedback theory to incorporate numerous other feedback mechanisms and test how mycorrhizal types mediate the net feedback effects that could propagate to shape large‐scale forest structures and dynamics.

Plant–soil feedback is dependent on tree mycorrhizal types and tree species richness in a subtropical forest

Plant-soil feedback (PSF) is an important driver of plant species coexistence and diversity maintenance. However, it remains unclear how changes in PSF due to decline in tree species richness influence the performance of arbuscular mycorrhizal (AM) and ectomycorrhizal (EcM) tree species. A PSF experiment was established with eight target tree species (four AM and four EcM tree species) based on a subtropical forest Biodiversity-Ecosystem Functioning Experimental in China (BEF-China) platform, where soil inocula were collected beneath the canopy of target tree species individuals growing in monoculture and eight tree-species mixture plots. We hypothesized that the negative PSF strength of AM tree species would be stronger in monocultures than that in eight tree-species mixtures, resulting in better performance in highly diverse plant communities, whereas EcM tree species would benefit less from tree species richness. However, the results showed consistent PSFs of AM tree species regardless of tree species richness. In contrast, EcM tree species experienced a change from positive in monocultures to negative PSF in eight tree-species mixtures, influencing the performance of EcM tree seedlings. With high concern of the cascading effects of tree species richness on PSFs via modulating soil fungal communities, we revealed that the alterations in EcM fungal abundance, putatively pathogenic fungal diversity, and fungal co-occurrence network complexity mirrored those of PSF associated with EcM tree species, showing the changes from positive in monocultures to negative feedback in eight tree-species mixtures. Our findings highlight the differential PSFs exhibited by AM and EcM tree species in response to tree species richness, and provide insight into the potential role of fungal functional guilds and co-occurrence network complexity in shaping the PSFs of them.

Plant-soil feedback and plant invasion: effect of soil conditioning on native and invasive Prosopis species using the plant functional trait approach.

Invasive species have been identified as a major threat to native biodiversity and ecosystem functioning worldwide due to their superiority in spread and growth. Such superiority is explained by the invasional meltdown phenomena, which suggests that invasive species facilitate the establishment of more invasive species rather than native species by modifying the plant-soil feedback (PSF). We conducted a two-phase plant-soil feedback experiment using the native Prosopis cineraria and the invasive Prosopis juliflora in Oman. Firstly, we conditioned the soil by planting seedlings of native species, invasive species, native and invasive species "mixed", and unconditioned soil served as a control. Secondly, we tested the feedback of these four conditioned soil on the two species separately by measuring the productivity (total biomass) and the performance in the form of plant functional traits (plant height, specific leaf area (SLA), leaf nitrogen content (Nmass), leaf carbon content (Cmass) and specific root length (SRL) of native and invasive species as well as the nutrient availability in soil (soil organic carbon (SOC) and soil total nitrogen (STN)). We found that the native species produced more biomass, best performance, and higher SOC and STN when grown in soil conditioned by native species, additionally, it gave lower biomass, reduced performance, and lower SOC and STN when grown in the soil conditioned by invasive and mixed species. These results suggest negative PSF for native species and positive PSF for invasive species in the soil conditioned by invasive species, which can be considered as red flag concerning the restoration of P. cineraria as an important native species in Oman, as such positive PSF of the invasive species P. juliflora will inhibit the regeneration of P. cineraria.

Abiotic legacies mediate plant–soil feedback during early vegetation succession on rare earth element mine tailings

Abstract An increasing number of studies have shown how feedback interactions between plants and soil can influence primary and secondary succession. However, very little is known about the patterns and mechanisms of such plant–soil feedbacks on stressed mine tailings ecosystem, which can be severely contaminated by a range of toxic elements. In a two‐phase plant–soil feedback experiment based on the rare earth element (REE) mine tailing soil, we investigated biotic (changes in bacterial and fungal communities) and abiotic (changes in chemical properties) legacies of three pioneer grass species, and examined feedback effects of three grasses, two legumes and two woody plants with different root traits. Positive plant–soil feedbacks were found in Miscanthus sinensis, Paspalum thunbergii and Tephrosia candida, and neutral feedbacks were observed in the other four plants. These effects corresponded with an increase in nutrients and total organic carbon, as well as a decrease in acidity and extractable aluminium and REEs. There were less signs of biotic changes in the conditioned tailings. The correlation analysis suggested a relationship between plants' responses to soil legacies and root traits, as well as root economics spectrum. On the mine tailings, acquisitive species with higher specific root length appeared to have greater potential for positive feedback. Synthesis and application. Our study shows that early succession on contaminated rare earth element mine tailings may lead to more positive plant–soil feedback than predicted based on results of non‐contaminated soils, mainly due to the alleviation of abiotic stress in tailings. Therefore, the improvement of specific abiotic soil stress and the trait‐based selection of acquisitive plants should be preferentially considered to promote the primary restoration of degraded land.

Plant-soil feedback across spatiotemporal scales from immediate effects to legacy

Plants and soil biota are important ecosystem engineers interacting via plant-soil feedback on large gradient of temporal scales from immediate interactions to long term legacy, which also operate on various spatial scales. Here I emphasize three major pathways of plant-soil feedbacks: i) the biota pathway, when plants affect soil biota, such as plant symbionts or antagonists, which affect plants, ii) the soil pathway, when plants affect soil environment, which then feedbacks to plants and finally iii) the biota-soil pathway, when plants affect soil biota, which then affect soil environment, which then effect plants. Living plant roots are major driver for biota pathway, which is more important for immediate effect, while litter largely supports the biota-soil pathway important for legacy effects. Many processes that have immediate effects, produce also small but more persistent changes in soil. Legacy is produced by accumulation of this small changes over time. This is supported by soil ability to preserve and accumulate, these small changes. Legacy also alternate outcome of immediate interactions between plants, soil and soil biota. The soil property changes, caused by legacy, happen either as slow gradual changes, or relatively fast, abrupt shifting between two steady states. In both cases, soil changes can reach tipping points, altering functioning of whole plant soil system. Apart from plants, also soil conditions or soil biota can be manipulated either intentionally (e.g. by land uses change, various agriculture, forestry or ecosystem restoration practices), or non-intentionally (e.g. biological invasion), which trigger changes in plant – soil - soil biota interactions as described above and cause immediate and legacy effects. Examples, presented in this review, suggest that legacy effect is particularly important in soils in early stages of pedogenesis or during response to or recovery after disturbance. Review highlight necessity studying plant soil feedback on all relevant spatiotemporal scales.

Travelling waves due to negative plant–soil feedbacks in a model including tree life-stages

The emergence and maintenance of tree species diversity in tropical forests is commonly attributed to the Janzen–Connell (JC) hypothesis, which states that growth of seedlings is suppressed in the proximity of conspecific adult trees. As a result, a JC distribution due to a density-dependent negative feedback emerges in the form of a (transient) pattern where conspecific seedling density is highest at intermediate distances away from parent trees. Several studies suggest that the required density-dependent feedbacks behind this pattern could result from interactions between trees and soil-borne pathogens. However, negative plant–soil feedback may involve additional mechanisms, including the accumulation of autotoxic compounds generated through tree litter decomposition. An essential task therefore consists in constructing mathematical models incorporating both effects showing the ability to support the emergence of JC distributions.In this work, we develop and analyse a novel reaction–diffusion-ODE model, describing the interactions within tropical tree species across different life stages (seeds, seedlings, and adults) as driven by negative plant–soil feedback. In particular, we show that under strong negative plant–soil feedback travelling wave solutions exist, creating transient distributions of adult trees and seedlings that are in agreement with the Janzen–Connell hypothesis. Moreover, we show that these travelling wave solutions are pulled fronts and a robust feature as they occur over a broad parameter range. Finally, we calculate their linear spreading speed and show its (in)dependence on relevant nondimensional parameters.

Root-exuded benzoxazinoids can alleviate negative plant-soil feedbacks.

Plants can suppress the growth of other plants by modifying soil properties. These negative plant-soil feedbacks are often species-specific, suggesting that some plants possess resistance strategies. However, the underlying mechanisms remain largely unknown. Here, we investigated whether benzoxazinoids, a class of dominant secondary metabolites that are exuded into the soil by maize and other cereals, allow maize plants to cope with plant-soil feedbacks. We find that three out of five tested crop species reduce maize (Zea mays L.) performance via negative plant-soil feedbacks relative to the mean across species. This effect is partially alleviated by the capacity of maize plants to produce benzoxazinoids. Soil complementation with purified benzoxazinoids restores the protective effect for benzoxazinoid-deficient mutants. Sterilization and reinoculation experiments suggest that benzoxazinoid-mediated protection acts via changes in soil biota. Substantial variation of the protective effect between experiments and soil types illustrates context dependency. In conclusion, exuded plant secondary metabolites allow plants to cope with plant-soil feedbacks. These findings expand the functional repertoire of plant secondary metabolites and reveal a mechanism by which plants can resist negative effects of soil feedbacks. The uncovered phenomenon may represent a promising avenue to stabilize plant performance in crop rotations.

Temporal dynamics of plant−soil feedback and related mechanisms depend on environmental context during invasion processes of a subtropical invader

Temporal dynamics of plant−soil feedback and related mechanisms depend on environmental context during invasion processes of a subtropical invader

Product-inhibition feedbacks, not microbial population level tradeoffs or soil pH, regulate decomposition potential under nutrient eutrophication

Global eutrophication of growth-limiting nutrients for plants and microbes, including nitrogen (N) and phosphorus (P), can cause enzymatic feedbacks at different levels of biological organization that in turn drive soil organic matter (SOM) decomposition. Because land management practices, such as fire in mesic grasslands, also impact nutrient availability, it is important to understand how soil feedbacks may manifest under multifactorial change. Here, using a thirty-year field experiment that crosses N- and P-fertilization (alone and in combination) with contrasting fire treatments (annual burning and fire suppression) in a tallgrass prairie ecosystem, we evaluated evidence for three possible feedbacks (product-inhibition, enrichment of fast-growing copiotrophic taxa, and soil pH shift) by measuring soil extracellular enzyme activities (EEAs) and microbial community composition (16S rRNA genes) monthly for a year. Consistent with product-inhibition feedback predictions, both N-fertilization and fire suppression (which increases soil N availability) decreased N-acquiring relative to C-acquiring EEAs, suggesting reduced N limitation. P-fertilization did not lower acid phosphatase activity, thus the product-inhibition feedback hypothesis was not supported under P eutrophication conditions. Although N- and P-fertilization, alone and in combination, did decrease putatively oligotrophic populations in favor of putatively copiotrophic populations, the hypothesized tradeoff for faster growth, a concomitant decrease in all soil EEAs, was only observed in unburned soils fertilized with N. Finally, observed changes in EEAs were not driven by acidification, in contrast to other fertilization experiments. Overall, results suggest that higher N availability affects enzymatic feedbacks primarily through product-inhibition, but a threshold-like growth tradeoff (copiotrophic) response is possible under the combination of fire suppression and N-fertilization. Inherent soil properties may modulate site-specific responses to fertilization, as evidenced by weak pH and EEA responses to N- and P-fertilization, respectively. Finally, soil microbial community change following chronic fertilization did not reliably predict the “copiotrophic” feedback of reduced SOM decomposition potential.

Plant–soil feedbacks among boreal forest species

Abstract Plant–microbial interactions in soils are considered to play a central role in regulating biodiversity in many global ecosystems. However, studies on plant–soil feedbacks (PSFs) and how these affect forest stand patterns in boreal regions are rare. We conducted a fully reciprocal PSF glasshouse experiment using four boreal tree species. Alnus glutinosa, Betula pendula, Picea abies and Pinus sylvestris seedlings were grown under controlled conditions in sterilised soil with or without soil inoculum collected under mature trees of each of the four species. Bacterial, fungal and oomycete communities in the rhizosphere were investigated using metabarcoding and correlated with differences in plant biomass. Alder grew best in conspecific soil, whereas birch grew equally well in all soil types. Pine and spruce grew best in heterospecific soil, particularly in soil from their successional predecessor. Ectomycorrhizal fungi (EMF) enhanced the growth of most seedlings, and Actinomycetota supported alder and birch growth and fungal plant pathogens hampered pine growth. Increased growth was linked to the ability of trees to recruit specific EMF and root‐associated fungi in heterospecific soils. Synthesis. This study experimentally examines the influence of root‐associated microbiota on the growth of boreal tree species. The observed plant–soil feedbacks mirror the successional patterns found in boreal forests, suggesting a possible contribution of soil microbiota to the successional progression. Species‐specific ectomycorrhizal fungi and a few bacteria rather than fungal plant pathogens or oomycetes seem to drive the feedbacks by promoting seedling growth in heterospecific soils.

Responses of Soil Microbial Survival Strategies and Functional Changes to Wet-Dry Cycle Events.

Soil microbial taxa have different functional ecological characteristics that influence the direction and intensity of plant-soil feedback responses to changes in the soil environment. However, the responses of soil microbial survival strategies to wet and dry events are poorly understood. In this study, soil physicochemical properties, enzyme activity, and high-throughput sequencing results were comprehensively anal0079zed in the irrigated cropland ecological zone of the northern plains of the Yellow River floodplain of China, where Oryza sativa was grown for a long period of time, converted to Zea mays after a year, and then Glycine max was planted. The results showed that different plant cultivations in a paddy-dryland rotation system affected soil physicochemical properties and enzyme activity, and G. max field cultivation resulted in higher total carbon, total nitrogen, soil total organic carbon, and available nitrogen content while significantly increasing α-glucosidase, β-glucosidase, and alkaline phosphatase activities in the soil. In addition, crop rotation altered the r/K-strategist bacteria, and the soil environment was the main factor affecting the community structure of r/K-strategist bacteria. The co-occurrence network revealed the inter-relationship between r/K-strategist bacteria and fungi, and with the succession of land rotation, the G. max sample plot exhibited more stable network relationships. Random forest analysis further indicated the importance of soil electrical conductivity, total carbon, total nitrogen, soil total organic carbon, available nitrogen, and α-glucosidase in the composition of soil microbial communities under wet-dry events and revealed significant correlations with r/K-strategist bacteria. Based on the functional predictions of microorganisms, wet-dry conversion altered the functions of bacteria and fungi and led to a more significant correlation between soil nutrient cycling taxa and environmental changes. This study contributes to a deeper understanding of microbial functional groups while helping to further our understanding of the potential functions of soil microbial functional groups in soil ecosystems.

Modelling how negative plant–soil feedbacks across life stages affect the spatial patterning of trees

In this work, we theoretically explore how litter decomposition processes and soil-borne pathogens contribute to negative plant–soil feedbacks, in particular in transient and stable spatial organisation of tropical forest trees and seedlings known as Janzen-Connell distributions. By considering soil-borne pathogens and autotoxicity both separately and in combination in a phenomenological model, we can study how both factors may affect transient dynamics and emerging Janzen–Connell distributions. We also identify parameter regimes associated with different long-term behaviours. Moreover, we compare how the strength of negative plant–soil feedbacks was mediated by tree germination and growth strategies, using a combination of analytical approaches and numerical simulations. Our interdisciplinary investigation, motivated by an ecological question, allows us to construct important links between local feedbacks, spatial self-organisation, and community assembly. Our model analyses contribute to understanding the drivers of biodiversity in tropical ecosystems, by disentangling the abilities of two potential mechanisms to generate Janzen-Connell distributions. Furthermore, our theoretical results may help guiding future field data analyses by identifying spatial signatures in adult tree and seedling distribution data that may reflect the presence of particular plant–soil feedback mechanisms.

Are Plant-Soil Feedbacks Caused by Many Weak Microbial Interactions?

We used high-throughput sequencing and multivariate analyses to describe soil microbial community composition in two four-year field plant-soil feedback (PSF) experiments in Minnesota, USA and Jena, Germany. In descending order of variation explained, microbial community composition differed between the two study sites, among years, between bulk and rhizosphere soils, and among rhizosphere soils cultivated by different plant species. To try to identify soil organisms or communities that may cause PSF, we correlated plant growth responses with the microbial community composition associated with different plants. We found that plant biomass was correlated with values on two multivariate axes. These multivariate axes weighted dozens of soil organisms, suggesting that PSF was not caused by individual pathogens or symbionts but instead was caused by 'many weak' plant-microbe interactions. Taken together, the results suggest that PSFs result from complex interactions that occur within the context of a much larger soil microbial community whose composition is determined by factors associated with 'site' or year, such as soil pH, soil type, and weather. The results suggest that PSFs may be highly variable and difficult to reproduce because they result from complex interactions that occur in the context of a larger soil microbial community.

Seedling performance in a dioecious tree species is similar near female and male conspecific adults despite differences in colonization by arbuscular mycorrhizal fungi

Plant–soil feedbacks (PSFs) are a key driver of species diversity and composition in plant communities worldwide; however, the factors that may cause feedbacks to vary within species are rarely examined. In dioecious species, the strength of feedbacks may differ near female plants that produce seed versus near male plants (which do not) because repeated inputs of seeds and high seedling densities near females may cause accumulation of host‐specific soil microbes that influence seedling performance. To test whether conspecific seedling performance is reduced near seed‐producing female trees relative to male or heterospecific trees, we conducted shadehouse and field experiments with a dioecious tropical tree species, Virola surinamensis (Myristicaceae), on Barro Colorado Island, Panama. The shadehouse experiment isolated the effect of soil microbial communities on seedling growth and allowed us to quantify colonization by mutualistic arbuscular mycorrhizal (AM) fungi, while the field experiment allowed us to assess seedling survival and growth in the presence of nearby conspecific adults and seedlings. In both experiments, seedling performance was similar between seedlings grown in the soil microbial communities and field environments underneath female conspecific, male conspecific, and heterospecific trees. However, contrary to expectation, seedling colonization by AM fungi was higher in male conspecific soil microbial communities than in female or heterospecific soil microbial communities at the end of the shadehouse experiment. Together, our experiments show that while differences among female and male plants in dioecious species may influence the association of conspecific seedlings with AM fungi in their soils, this variation does not necessarily translate directly to differences in seedling performance, at least over the time frame of our experiments. Studies of additional dioecious species are needed to help determine differences in soil microbial communities beneath male and female plants and to assess the role of seed input versus adult root systems in driving PSFs.

Plant–Soil Feedback of Companion Species during Grassland Community Succession

The responses of dominant species to plant–soil feedback (PSF) are well established; however, the changes in the PSF of companion species remain unclear. This study aims to assess the direction and intensity of PSF, determine the main factors influencing it, and interpret the ecological significance of PSF in companion species within the context of grassland community succession. Three typical companion species, namely Artemisia sacrorum, Artemisia capillaris, and Artemisia giraldii, were planted in soils at three grassland community succession stages (early, middle, and late) on the Loess Plateau. Our results indicate that during both plant growth periods, the shoot biomass of A. sacrorum, A. capillaris, and A. giraldii in early- and late-stage soils was higher than that in the middle-stage soil, suggesting consistent growth of the three companion species during the two growth periods. However, plant growth simultaneously led to a reduction in soil nutrient content and microbial biomass, resulting in an overall decrease in the biomass of the three species, indicating a negative PSF effect in companion species. In conclusion, the negative PSF observed in all three associated species explains the temporary dominance of companion species during succession. This study enhances our understanding of the mechanisms driving PSF in community succession.

Application of Multi-Plant Symbiotic Systems in Phytoremediation: A Bibliometric Review

The bibliometric analysis technique was used to retrieve 232 relevant publications from the Web of Science core database published between 2002 and 2022. The basic characteristics of the literature were analyzed, and keyword co-occurrence analysis and literature co-citation analysis were performed. The results demonstrated the following: (1) The total number of publications on phytoremediation utilizing a multi-plant symbiosis system increased year by year, indicating that multi-plant symbiosis systems have garnered significant interest in the field of phytoremediation in recent years. (2) “Short rotation coppice” (#0), “straw” (#1), “heavy metal” (#2), “soil enzymes” (#3), “glomus caledonium” (#4), and “phenanthrene” (#5) comprise the research hotspots in this field both domestically and internationally, where the #0 clusters, #2 clusters, and #5 clusters indicate that the application of multi-plant combinations has not formed a new branch in the field of phytoremediation during 2007–2017. In addition, the #1 clusters, #3 clusters, and #4 clusters indicate that the safety of agricultural land, the mechanism of action of soil enzymes, and arbuscular mycorrhizal fungi comprise research hotspots in recent years. (3) “Heavy metal contamination” (#0), “agro-mining” (#1), “Leguminosae” (#2), “soil enzymes” (#3), “soil microbial community” (#4), and “Salix caprea” (#5) constitute the domestic and international knowledge base of this field, with a study of soil microbial communities regarded as the cutting-edge branch of this field. (4) The specific influencing factors of multi-plant symbiotic systems include plant diversity, interspecific relationships, and the gender of plant species, and the mechanisms of action include the plant–soil feedback mechanism, enhanced plant resistance mechanism, increased detoxification pathway, and plant–plant interaction mechanism. Finally, future research on phytoremediation using multi-plant symbiotic systems should focus on the following four aspects: exploring the applicable environment of multi-plant symbiotic systems as a remediation strategy; analyzing the remediation mechanism from multiple perspectives: atmosphere–plant–soil; combining physicochemical and biological technologies to improve remediation efficiency; and establishing a dynamic model to evaluate remediation effects.