Plant Interactions Research Articles

Trophic level interactions of host plant’s biophysical traits with insect pests and natural enemies on three jasmine species: a principal component analysis

Trophic level interactions of host plant’s biophysical traits with insect pests and natural enemies on three jasmine species: a principal component analysis

Rewiring of Aminoacyl-tRNA Synthetase Localization and Interactions in Plants With Extensive Mitochondrial tRNA Gene Loss.

The number of tRNAs encoded in plant mitochondrial genomes varies considerably. Ongoing loss of bacterial-like mitochondrial tRNA genes in many lineages necessitates the import of nuclear-encoded counterparts that share little sequence similarity. Because tRNAs are involved in highly specific molecular interactions, this replacement process raises questions about the identity and trafficking of enzymes necessary for the maturation and function of newly imported tRNAs. In particular, the aminoacyl-tRNA synthetases (aaRSs) that charge tRNAs are usually divided into distinct classes that specialize on either organellar (mitochondrial and plastid) or nuclear-encoded (cytosolic) tRNAs. Here, we investigate the evolution of aaRS subcellular localization in a plant lineage (Sileneae) that has experienced extensive and rapid mitochondrial tRNA loss. By analyzing full-length mRNA transcripts (PacBio Iso-Seq), we found predicted retargeting of many ancestrally cytosolic aaRSs to the mitochondrion and confirmed these results with colocalization microscopy assays. However, we also found cases where aaRS localization does not appear to change despite functional tRNA replacement, suggesting evolution of novel interactions and charging relationships. Therefore, the history of repeated tRNA replacement in Sileneae mitochondria reveals that differing constraints on tRNA/aaRS interactions may determine which of these alternative coevolutionary paths is used to maintain organellar translation in plant cells.

Assessing the accuracy of paired and random sampling for quantifying plant–plant interactions in natural communities

AbstractPlant interactions in extreme environments are often inferred from spatial associations and quantified by means of paired sampling. Yet, this method might be confounded by habitat‐sharing effects. Here, we address whether paired and random sampling methods provide similar results at varying levels of environmental heterogeneity. We quantified spatial associations with the two methods at three sites that encompass different micro‐environmental heterogeneity and stress levels: Mediterranean environments in Canary Islands, Spain, and Sardinia, Italy, and a cold alpine environment in Hokkaido, Japan. Then, we simulated plant communities with different levels of species micro‐habitat preferences, environmental heterogeneity, and stress levels. We found that differences in species associations between paired and random sampling were indistinguishable from zero in a homogeneous space. When simulating codispersion over a decreasing abundance gradient, both sampling methods correctly identified facilitation and distinguished it from codispersion. Yet, the pairwise method provided higher facilitation estimates than the random one. At each site, there were strong differences between beneficiary species in their spatial association with nurse species, and associations became more positive with increasing stress in Spain. Most importantly, there were no differences in results yielded by the two methods at any of the different stress levels at the Spanish and Japanese sites. At the Italian site, although micro‐environmental heterogeneity was low, we found weakly significant differences between methods that were unlikely due to habitat‐sharing effects. Thus, the paired sampling method can provide significant insights into net and long‐term effects of plant interactions in spatially conspicuous environments.

BRUTUS-LIKE (BTSL) E3 ligase-mediated fine-tuning of Fe regulation negatively affects Zn tolerance of Arabidopsis.

The mineral micronutrients zinc (Zn) and iron (Fe) are essential for plant growth and human nutrition, but interactions between the homeostatic networks of these two elements are not fully understood. Here we show that loss of function of BTSL1 and BTSL2, which encode partially redundant E3 ubiquitin ligases that negatively regulate Fe uptake, confers tolerance to Zn excess in Arabidopsis thaliana. Double btsl1 btsl2 mutant seedlings grown on high Zn medium accumulated similar amounts of Zn in roots and shoots to the wild type, but suppressed the accumulation of excess Fe in roots. RNA-sequencing analysis showed that roots of mutant seedlings had relatively higher expression of genes involved in Fe uptake (IRT1, FRO2, and NAS) and in Zn storage (MTP3 and ZIF1). Surprisingly, mutant shoots did not show the transcriptional Fe deficiency response which is normally induced by Zn excess. Split-root experiments suggested that within roots the BTSL proteins act locally and downstream of systemic Fe deficiency signals. Together, our data show that constitutive low-level induction of the Fe deficiency response protects btsl1 btsl2 mutants from Zn toxicity. We propose that BTSL protein function is disadvantageous in situations of external Zn and Fe imbalances, and formulate a general model for Zn-Fe interactions in plants.

Arbuscular mycorrhiza changes plant facilitation patterns and increases resource use efficiency in intercropped annual plants

Arbuscular mycorrhizal fungi (AMF) play a vital role in mediating rhizosphere interactions and plant growth, especially in resource-constrained soils. However, few studies have documented the effects of AMF on plant–plant interaction patterns and resource use efficiency along stress gradients. In this study, a growth environment-controlled experiment was carried out to evaluate the effects of AMF inoculation on maize-grass pea intercropping along three phosphorus (P) and two water gradients. The data indicated that soil water and P availability determined the plant interspecific interaction pattern, and that interaction was strongly mediated by AMF inoculation. Grass pea and maize were mutually facilitated under low P and water conditions and transitioned to a new pattern, i.e., that maize was facilitated but grass pea was neutral role or facilitator with increasing resource availability. The facilitative effect was particularly significant under P- and water-deficient conditions. Moreover, the transition of the plant–plant interaction pattern was mechanically driven by improving rhizospheric phosphatase activities by 5.08–20.02 %, rhizospheric acidification and enhanced microbial activities under resource deficit conditions. Critically, AMF inoculation was observed to significantly improve rhizospheric soil P availability and microbial biomass (p < 0.05); however, it enhanced the complementary utilization of P and water and weakened interspecific competition under high-resource conditions. Therefore, AMF inoculation positively transformed the plant–plant interaction pattern along resource gradients for higher P, nitrogen and water use efficiency. This study validates the context-dependent interspecific interaction and the role of AMF in optimizing resource use in a nutrient-impoverished intercropping system.

Fine‐scale variation in the effect of the cushion plantAzorella selagoon vascular plants, mosses, hepatics and lichens in the sub‐Antarctic

AbstractQuestionPlant–plant interactions can strongly influence community structure and composition. The outcome of these interactions can vary considerably across space and is often linked to environmental conditions, with, for example, a higher prevalence of facilitative interactions typically being observed under greater environmental severity. To date, most studies have documented shifts from competitive to facilitative (or neutral) plant–plant and plant–lichen interactions along gradients of increasing environmental severity from pairwise interspecific interactions. However, few studies have examined if the outcome of these interactions for different taxonomic groups is dependent on environmental conditions across multiple environmental stress gradients.LocationSub‐Antarctic Marion Island.MethodsWe examine community‐level variation in the response of four taxa (i.e., vascular plants, hepatics, mosses, and lichens) to an interaction with a long‐lived cushion plant species (Azorella selago) that ameliorates microenvironmental conditions, testing how the effect of the cushion plant on the taxa varies along multiple stress gradients at the scale of a landform.ResultsContrary to expectations, even when considering multiple proximate predictor variables, fine‐scale spatial variation in the effect ofA. selagoon the taxa could not be explained. However, the outcome of the interaction withA. selagodiffered between taxonomic groups, with vascular plants benefitting and the non‐vascular taxa experiencing neutral or negative impacts.ConclusionsThis study highlights that the impacts of biotic interactions cannot always be generalized across plant groups, and that it is necessary to consider taxon‐specific responses when predicting community‐level impacts of biotic interactions. More generally, we demonstrate how complex spatial variation in environmental stressors can be explicitly considered when modelling variation in the outcome of plant–plant interactions.

Small‐scale heterogeneity shapes grassland diversity in low‐to‐intermediate resource environments

AbstractQuestionsSoil resource heterogeneity influences the outcome of plant–plant interactions and, consequently, species co‐existence and diversity patterns. The magnitude and direction of heterogeneity effects vary widely, and the processes underlying such variations are not fully understood. In this study, we explored how and under what resource conditions small‐scale heterogeneity modulates grassland plant diversity.LocationOderhänge Mallnow, Potsdam, Brandenburg, Germany.MethodsWe expanded the individual‐based plant community model (IBC‐grass) to incorporate dynamic below‐ground resource maps, simulating spatial heterogeneity of resource availability. Empirical centimeter‐scale data of soil C/N ratio were integrated into the model, accounting for both configurational and compositional heterogeneity. We then analyzed the interplay between small‐scale heterogeneity and resource availability on the interaction and co‐existence of plant species and overall diversity.ResultsOur results showed significant differences between the low‐ and high‐resource scenarios, with both configurational and compositional heterogeneity having a positive effect on species richness and Simpson's diversity, but only under low‐resource conditions. As compositional heterogeneity in the fine‐scale C/N ratio increased, we observed a positive shift in Simpson's diversity and species richness, with the highest effects at the highest level of variability tested. We observed little to no effect in nutrient‐rich scenarios, and a shift to negative effects at the intermediate resource level. The study demonstrates that site‐specific resource levels underpin how fine‐scale heterogeneity influences plant diversity and species co‐existence, and partly explains the divergent effects recorded in different empirical studies.ConclusionsThis study provides mechanistic insights into the complex relationship between resource heterogeneity and diversity patterns. It highlights the context‐dependent effects of small‐scale heterogeneity, which can be positive under low‐resource, neutral under high‐resource, and negative under intermediate‐resource conditions. These findings provide a foundation for future investigations into small‐scale heterogeneity–diversity relationships, contributing to a deeper understanding of the processes that promote species co‐existence in plant communities.

Biotic and abiotic factors shaping bat activity in Maryland soybean fields

AbstractBats are important pest control agents in agriculture. Yet, the underlying fine‐scale biotic and abiotic mechanisms that drive their foraging behaviors and responses to insect outbreaks are unclear. Herbivore‐induced plant volatiles (HIPVs) can attract both invertebrate and vertebrate natural enemies that use the chemical plant cues to locate insect prey. The ability of HIPVs to attract multiple species raises the question of whether they may also be a biotic factor influencing insectivorous bat activity. Additionally, abiotic factors, such as weather conditions, can affect bat activity in agricultural settings, but little is known about how bats respond to shifting environmental conditions on short timescales in this landscape context. Using a model crop system, soybean (Glycine max), our study asked three questions: (1) Which bat species are active in eastern Maryland soybean fields? (2) Is insectivorous bat activity affected by naturally occurring soybean HIPVs and/or synthetic soybean HIPVs (indole or farnesene)? (3) How is insectivorous bat activity affected by hourly weather conditions in this landscape? In soybean fields in eastern Maryland, we created paired treatment plots: HIPV plots (damaged plants or synthetic HIPV dispensers) and control plots (undamaged plants or empty dispensers). We measured bat activity using ultrasonic recorders, summarizing hourly and nightly activity, and detected 10 total species. The most abundant species were big brown/silver‐haired bats (Eptesicus fuscus/Lasionycteris noctivagans). Bat activity did not significantly differ between control and HIPV plots in any of the three experiments. Thus, our results do not support our expectation that bats in eastern Maryland use soybean HIPVs to locate insect prey. However, bat activity did increase with increasing average hourly temperature and wind speed. This initial study of bats and HIPVs, as well as the fine‐scale examination of weather conditions on bat activity, may serve as a guide for future research on bat–plant interactions that can support the development of new strategies for sustainable pest management.

Isolation and identification of endophytic actinobacteria from Iris persica and Echium amoenum plants and investigation of their effects on germination and growth of wheat plant.

Plant biotechnology helps to develop different types of new products with increased resistance to disease, greater tolerance to drought and salt stress, and better nutritional value. The interaction of plants and microorganisms will play a significant role to achieve this purpose. The aims of this study were to isolate endophyte Actinobacteria strains of some medicinal plants and the investigation of their bioactive potential. 15 Actinobacteria strains were selectively isolated from Persian iris and Echium amoenum plants, and then their belonging to Actinobacteria phylum was confirmed using an Actinobacteria-specific primer pair. The antioxidant activity of the crude extract obtained from the isolated strains was investigated based on DPPH method. Investigating the antioxidant activity of the crude extract showed that at a concentration of 100 μg/mL, the two strains EG1 and EG2 had 71% and 78% antioxidant activity, respectively. According to the phylogeny studies, it was determined that two strains belonged to the Streptomyces genus. The effect of supernatant achieved from selected endophytic strain on 35-day wheat plants showed that the supernatant considerably promotes root and shoot growth and chlorophyll content under salinity stress (150 mM NaCl). In general, it can be concluded strains that live symbiotically with medicinal plants are rich sources of bioactive compounds. Therefore, identification of the bioactive compounds in the extract of isolated Actinobacteria from medicinal plants and further studies on their metabolism are suggested.

On the Negative Impact of Mycorrhiza Application on Maize Plants (Zea mays) Amended with Mineral and Organic Fertilizer.

Many studies describe the positive effect of mycorrhiza, but few report on negative effects. Furthermore, there is a research gap on the mechanisms under which conditions the symbiotic mycorrhizal plant interaction or a parasitic one predominates. The study was conducted as a field experiment over three years to investigate the effect of mycorrhiza (Rhizoglomus intraradices) and soil bacteria applications on fertile soil. A standard fertilizer (diammonium phosphate) and two microgranular fertilizers (mineral and organomineral) were applied alone or in combination with the biostimulants mycorrhiza and/or soil bacteria (Bacillus velezensis). The application of the mycorrhiza as the only biostimulant resulted in lower yields compared to all fertilizer variants without the mycorrhiza or with mycorrhiza in combination with soil bacteria in the dry years 2015 (p = 0.0241) and 2016 (p = 0.0003). The usage of soil bacteria alone, or soil bacteria with fertilizer, resulted in few occasional significant differences. The combination with soil bacteria raised the yield of mycorrhiza-treated fertilizer variants to a significant extent in 2015 (p = 0.0007) and 2016 (p = 0.0019). The negative effects of mycorrhiza application in this study were alleviated by the simultaneous use of soil bacteria. Treatments with organomineral microgranular fertilizer, which were expected to promote the naturally occurring soil microbiome more than the mineral fertilizer variants, were most negatively affected by the mycorrhiza. We hypothesize that the naturally occurring microbiome of the study site was already optimal for maize plants, and thus the successful introduction of other microorganisms through the application of the mycorrhiza and soil bacteria tended not to be beneficial. The present study is the first report on the negative influence of arbuscular mycorrhiza on maize yields gained with a standard fertilizer (diammonium phosphate) and two microgranular fertilizer, and the alleviation of that impact by combined application of soil bacteria. We conclude that the application of the used biostimulants may have negative impacts on maize yield if the soil is already rich in nutrients and water is the limiting factor.

Expression of EPL1 from Trichoderma atroviride in Arabidopsis Confers Resistance to Bacterial and Fungal Pathogens.

During plant interaction with beneficial microorganisms, fungi secrete a battery of elicitors that trigger plant defenses against pathogenic microorganisms. Among the elicitor molecules secreted by Trichoderma are cerato-platanin proteins, such as EPL1, from Trichoderma atroviride. In this study, Arabidopsis thaliana plants that express the TaEPL1 gene were challenged with phytopathogens to evaluate whether expression of EPL1 confers increased resistance to the bacterial pathogen Pseudomonas syringae and the necrotrophic fungus Botrytis cinerea. Infection assays showed that Arabidopsis EPL1-2, EPL1-3, EPL1-4 expressing lines were more resistant to both pathogens in comparison to WT plants. After Pseudomonas syringae infection, there were reduced disease symptoms (e.g., small chlorotic spots) and low bacterial titers in the three 35S::TaEPL1 expression lines. Similarly; 35S::TaEPL1 expression lines were more resistant to Botrytis cinerea infection, showing smaller lesion size in comparison to WT. Interestingly, an increase in ROS levels was detected in 35S::TaEPL1 expression lines when compared to WT. A higher expression of SA- and JA-response genes occurred in the 35S::TaEPL1 lines, which could explain the resistance of these EPL1 expression lines to both pathogens. We propose that EPL1 is an excellent elicitor, which can be used to generate crops with improved resistance to broad-spectrum diseases.

Brassinosteroid coordinates cell layer interactions in plants via cell wall and tissue mechanics.

Growth coordination between cell layers is essential for development of most multicellular organisms. Coordination may be mediated by molecular signaling and/or mechanical connectivity between cells, but how genes modify mechanical interactions between layers is unknown. Here we show that genes driving brassinosteroid synthesis promote growth of internal tissue, at least in part, by reducing mechanical epidermal constraint. We identified a brassinosteroid-deficient dwarf mutant in the aquatic plant Utricularia gibba with twisted internal tissue, likely caused by mechanical constraint from a slow-growing epidermis. We tested this hypothesis by showing that a brassinosteroid mutant in Arabidopsis enhances epidermal crack formation, indicative of increased tissue stress. We propose that by remodeling cell walls, brassinosteroids reduce epidermal constraint, showing how genes can control growth coordination between layers by means of mechanics.

Plant community stability is associated with a decoupling of prokaryote and fungal soil networks

Soil microbial networks play a crucial role in plant community stability. However, we lack knowledge on the network topologies associated with stability and the pathways shaping these networks. In a 13-year mesocosm experiment, we determined links between plant community stability and soil microbial networks. We found that plant communities on soil abandoned from agricultural practices 60 years prior to the experiment promoted destabilising properties and were associated with coupled prokaryote and fungal soil networks. This coupling was mediated by strong interactions of plants and microbiota with soil resource cycling. Conversely, plant communities on natural grassland soil exhibited a high stability, which was associated with decoupled prokaryote and fungal soil networks. This decoupling was mediated by a large variety of past plant community pathways shaping especially fungal networks. We conclude that plant community stability is associated with a decoupling of prokaryote and fungal soil networks and mediated by plant-soil interactions.

Diamondback moth egg susceptibility to rainfall: effects of leaf surface properties on the direct and indirect impact of simulated rain

AbstractDiamondback moth (DBM), Plutella xylostella L. (Lepidoptera: Plutellidae), eggs are vulnerable to rainfall, but the impact is dependent on host plant properties and the nature of oviposition sites. The effects of host plants, common cabbage (Brassica oleracea L. var. capitata) and Chinese cabbage (Brassica rapa L. var. pekinensis) (Brassicaceae), and oviposition sites on the fate of eggs subjected to simulated raindrops were investigated in laboratory experiments. In oviposition studies, DBM deposited more eggs on leaf veins than on leaf laminas on both host plants. In common cabbage plants, eggs laid on lower leaves (leaf 2) were less susceptible to dislodgment by rainfall than eggs laid on upper leaves (leaf 6). Eggs laid on the veins on the abaxial surfaces of leaves 2 and 6 of common cabbage plants were less susceptible to dislodgment by raindrops than eggs laid at other sites on this host plant. In Chinese cabbage plants, eggs laid on the veins were less susceptible to dislodgment by raindrops than eggs laid on leaf laminas. When DBM laid eggs in clusters, eggs were less susceptible to dislodgment by raindrops. The presence of waxes on leaf surfaces and concave veins affected egg placement and the retention of eggs at oviposition sites when subjected to raindrops. Eggs were more resistant to raindrops on the concave veined and less waxy leaves of Chinese cabbage plants than on waxy surfaces of smooth common cabbage leaves. When epicuticular wax crystals were removed from common cabbage leaves before oviposition, eggs were more resistant to dislodgment by raindrops. Leaf orientation or angle (horizontal plane vs. an angle of 45°) did not affect the susceptibility of eggs to raindrops. However, eggs were affected indirectly, and vibrations caused by the impact of raindrops resulted in egg removal from both adaxial and abaxial surfaces. Overall, eggs were less likely to be dislodged by raindrops when laid on concave veins and less waxy leaf surfaces. In oviposition tests, DBM laid fewer eggs on plant parts from which they were most easily removed by raindrops, and when they did lay eggs at these sites, they often deposited them in clusters which were more resistant than single eggs to removal by raindrops. The study reiterates the species‐specific nature of DBM‐host plant interactions and shows that female DBM can modify their behaviour to improve the probability of egg survival when substrates available for oviposition are sub‐optimal.

Biotechnological Tools to Elucidate the Mechanism of Plant and Nematode Interactions.

Plant-parasitic nematodes (PPNs) pose a threat to global food security in both the developed and developing worlds. PPNs cause crop losses worth a total of more than USD 150 billion worldwide. The sedentary root-knot nematodes (RKNs) also cause severe damage to various agricultural crops and establish compatible relationships with a broad range of host plants. This review aims to provide a broad overview of the strategies used to identify the morpho-physiological and molecular events that occur during RKN parasitism. It describes the most current developments in the transcriptomic, proteomic, and metabolomic strategies of nematodes, which are important for understanding compatible interactions of plants and nematodes, and several strategies for enhancing plant resistance against RKNs. We will highlight recent rapid advances in molecular strategies, such as gene-silencing technologies, RNA interference (RNAi), and small interfering RNA (siRNA) effector proteins, that are leading to considerable progress in understanding the mechanism of plant-nematode interactions. We also take into account genetic engineering strategies, such as targeted genome editing techniques, the clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR associated protein 9 (Cas9) (CRISPR/Cas-9) system, and quantitative trait loci (QTL), to enhance the resistance of plants against nematodes.

Back to the 'roots' of research: a hypothesis-driven approach provides predictive understanding of plant-herbivore-microbe interactions.

This article is a Commentary on Böttner et al. (2023), 239: 1475–1489.

Covariate-Informed Latent Interaction Models: Addressing Geographic & Taxonomic Bias in Predicting Bird–Plant Interactions

Reductions in natural habitats urge that we better understand species’ interconnection and how biological communities respond to environmental changes. However, ecological studies of species’ interactions are limited by their geographic and taxonomic focus which can distort our understanding of interaction dynamics. We focus on bird–plant interactions that refer to situations of potential fruit consumption and seed dispersal. We develop an approach for predicting species’ interactions that accounts for errors in the recorded interaction networks, addresses the geographic and taxonomic biases of existing studies, is based on latent factors to increase flexibility and borrow information across species, incorporates covariates in a flexible manner to inform the latent factors, and uses a meta-analysis dataset from 85 individual studies. We focus on interactions among 232 birds and 511 plants in the Atlantic Forest, and identify 5% of pairs of species with an unrecorded interaction, but posterior probability that the interaction is possible over 80%. Finally, we develop a permutation-based variable importance procedure for latent factor network models and identify that a bird’s body mass and a plant’s fruit diameter are important in driving the presence of species interactions, with a multiplicative relationship that exhibits both a thresholding and a matching behavior. Supplementary materials for this article are available online.

Pseudomonas syringae Type III Secretion Protein HrpP Manipulates Plant Immunity To Promote Infection.

The bacterial plant pathogen Pseudomonas syringae deploys a type III secretion system (T3SS) to deliver effector proteins into plant cells to facilitate infection, for which many effectors have been characterized for their interactions. However, few T3SS Hrp (hypersensitive response and pathogenicity) proteins from the T3SS secretion apparatus have been studied for their direct interactions with plants. Here, we show that the P. syringae pv. tomato DC3000 T3SS protein HrpP induces host cell death, suppresses pattern-triggered immunity (PTI), and restores the effector translocation ability of the hrpP mutant. The hrpP-transgenic Arabidopsis lines exhibited decreased PTI responses to flg22 and elf18 and enhanced disease susceptibility to P. syringae pv. tomato DC3000. Transcriptome analysis reveals that HrpP sensing activates salicylic acid (SA) signaling while suppressing jasmonic acid (JA) signaling, which correlates with increased SA accumulation and decreased JA biosynthesis. Both yeast two-hybrid and bimolecular fluorescence complementation assays show that HrpP interacts with mitogen-activated protein kinase kinase 2 (MKK2) on the plant membrane and in the nucleus. The HrpP truncation HrpP1-119, rather than HrpP1-101, retains the ability to interact with MKK2 and suppress PTI in plants. In contrast, HrpP1-101 continues to cause cell death and electrolyte leakage. MKK2 silencing compromises SA signaling but has no effect on cell death caused by HrpP. Overall, our work highlights that the P. syringae T3SS protein HrpP facilitates effector translocation and manipulates plant immunity to facilitate bacterial infection. IMPORTANCE The T3SS is required for the virulence of many Gram-negative bacterial pathogens of plants and animals. This study focuses on the sensing and function of the T3SS protein HrpP during plant interactions. Our findings show that HrpP and its N-terminal truncation HrpP1-119 can interact with MKK2, promote effector translocation, and manipulate plant immunity to facilitate bacterial infection, highlighting the P. syringae T3SS component involved in the fine-tuning of plant immunity.

Effects of Pesticides on the Arbuscular Mycorrhizal Symbiosis

Substantial amounts of pesticides, used in agricultural production to control pests, diseases, and weeds, and thereby attain high product quantities and quality, can severely affect the ecosystem and human health. The amounts of pesticides used depend on the specifics of the current production system but also exhibit large effects of past practices. Pesticides do not act only on the target organisms but also on organisms for which the chemicals were not specifically formulated, constituting hazardous molecules for humans and the environment. Pesticides, therefore, also influence soil microbial communities including organisms that engage in mutualistic plant symbioses that play a crucial role in its mineral nutrition, such as arbuscular mycorrhizal fungi. In this review, we summarize the current knowledge on the effects of synthetic and natural (‘green’) pesticides (fungicides, herbicides, and insecticides) on arbuscular mycorrhizal symbiosis. We deal with both the direct effects (spore germination and extraradical and intraradical growth of the mycelium) and indirect effects on the agroecosystem level. Such indirect effects include effects through the spread of herbicide-resistant crops and weeds to neighboring ecosystems, thereby modifying the mycorrhizal inoculum potential and altering the plant–plant interactions. We also briefly discuss the possibility that mycorrhizal plants can be used to enhance the phytoremediation of organic pesticides.

Belowground facilitation of plant mixtures on rhizosphere soil of Commelina communis grown on extremely Cu- and Cd-contaminated mine: From soil quality to bacterial community

Plant–plant interactions exert positive effects under stress conditions, but their impact on heavy metal-contaminated rhizosphere soil quality and bacterial community remains unclear. In this work, the rhizospheric soil of Cu-accumulator Commelina communis and neighboring plants grown in a heavily contaminated copper mine was analyzed to elucidate such belowground facilitation. Physicochemical properties and microbial characteristics of rhizospheric soil of control C. communis (far from neighboring plants), facilitated C. communis (near neighboring plants), and neighboring plants were compared. The average values of total organic carbon, NH4+-N, NO2−-N, NO3−-N, available phosphorus, urease, and phosphatase in the C. communis rhizosphere increased by 0.82-, 0.64-, 0.44-, 0.06-, 0.10-, 0.36-, and 0.30-fold in the presence of surrounding plants, respectively. The relative abundance of oligotrophic bacteria (Chloroflexi) decreased, whereas copiotrophic bacteria (Proteobacteria) increased in plant species mixtures. Venn graph and partial least squares discriminant analysis indicated that the composition of the bacterial community in the facilitated C. communis rhizosphere showed higher similarity to neighboring plants than to control C. communis. Among 49 predicted functional groups analyzed by FAPROTAX analysis, chemoheterotrophy (36.04 %) involved in carbon cycles had the highest relative abundance and increased in the facilitated C. communis rhizosphere due to the positive response of 193 OTUs (mainly belonging to Proteobacteria and Actinobacteriota) under plant–plant interactions. The increased relative abundance of Methylocella and Bradyrhizobium resulted in improved nitrogen fixation in the C. communis rhizosphere, whereas nitrate reduction with its main performer Rubrobacter was inhibited. The ecological function of rhizobiomes of the facilitated C. communis and neighbors also showed higher similarity compared with that of the control C. communis. These results show the role of neighboring plants in modulating soil quality and rhizobiomes of plant remediators under stress and more indoor garden experiments need to be conducted to verify such belowground facilitation.