Plant and Soil

The root anatomical phenotype root cortical aerenchyma (RCA) decreases the metabolic cost of soil exploration and improves plant growth under drought and low soil fertility. RCA may also change the microenvironment of rhizosphere microorganisms by increasing oxygen availability or by reducing carbon rhizodeposition. We tested the hypothesis that plants with contrasting expression of RCA have different rhizosphere prokaryotic communities. Maize inbreds were grown in two field sites, Limpopo Province, South Africa and Pennsylvania, USA, and their rhizosphere soil sampled at flowering. High- and low-nitrogen fertilization was imposed as separate treatments in the experiment in South Africa. The rhizosphere microbial composition of plants with contrasting RCA was characterized by metabarcoding of the 16S rRNA genes. Geographic location was the most important factor related to the composition of rhizosphere microbial communities. In the site in South Africa, RCA explained greater percent of variance (9%) in the composition of microbial communities than genotype (7%). Although other root anatomical and architectural phenotypes were studied as possible cofactors affecting the microbial composition, RCA was among the best significant explanatory variables for the South African site although it was neutral in the Pennsylvania site. High-RCA rhizospheres significantly enriched OTUs of the families Burkholderiaceae (in South Africa) and Bacillaceae (in USA), compared to low-RCA plants, and OTUs of the families Beijerinckiaceae and Sphingomonadaceae were enriched at the two nitrogen levels in high RCA plants in South Africa. Our results are consistent with the hypothesis that RCA is an important factor for rhizosphere microbial communities, especially under suboptimal nitrogen conditions.

Similar to the human gut microbiome, diverse microbes colonize the plant rhizosphere, and an imbalance of this microbial community, known as dysbiosis, may negatively impact plant health. This study aimed to investigate the influence of rhizosphere dysbiosis on above-ground plant health using tomato plants (Solanum lycopersicum L.) and the foliar bacterial spot pathogen Xanthomonas perforans as model organisms. Four-week-old tomato plants rhizospheres were treated with streptomycin (0.6 g x L-1), or water (negative control) and spray-inoculated with X. perforans (105 cells x mL-1) after 24 h. Half of the plants treated with streptomycin and X. perforans received soil microbiome transplants (SMT) from uninfected plant donors 48 h after streptomycin application. Streptomycin-treated plants showed a 26% increase in disease severity compared to plants that received no antibiotic, while plants that received the SMT had an intermediate level of disease severity. Antibiotic-treated plants showed a reduced abundance of rhizobacterial taxa like Cyanobacteria from the genus Cylindrospermum as well as down-regulation of genes related to plant primary and secondary metabolism and up-regulation of plant defense genes associated with induced systemic resistance (ISR). This study highlights the crucial role of beneficial rhizosphere microbes in disease resistance, even to foliar pathogens.

Growing evidence suggests that soil microbes can improve plant fitness under drought. However, in potato, the worlds most important non-cereal crop, the role of the rhizosphere microbiome under drought has been poorly studied. Using a cultivation independent metabarcoding approach, we examined the rhizosphere microbiome of two potato cultivars with different drought tolerance as a function of water regime (continuous versus reduced watering) and manipulation of soil microbial diversity (i.e., natural (NSM), vs. disturbed (DSM) soil microbiome). Water regime and soil pre-treatment showed a significant interaction with bacterial community composition of the drought-sensitive (HERBST) but not the drought-resistant cultivar (MONI). Depending on the cultivar, different taxa responded to reduced watering. Under NSM conditions, these were mostly rhizobiales order representative in MONI, and Streptomyces, Glycomyces, Marmoricola, Aeromicrobium, Mycobacterium, amongst Actinobacteriota, and the root endophytic fungus Falciphora in HERBST. Under DSM conditions and reduced watering, Bradyrhizobium, Ammoniphilus, Symbiobacterium and unclassified Hydrogenedensaceae responded in the rhizosphere of MONI compared to the continuous, while in HERBST, fewer taxa of Actinobacteriota and no fungi responded to reduced vs. continuous watering. Overall, our results indicate a strong cultivar specific relationship between potato and their associated rhizosphere microbiomes under reduced soil moisture.

The leaf microbiome plays an important role in plant health and defense. Despite its importance, how the assembly of the leaf microbial community is modified by environmental conditions such as nutrient availability remains relatively uninvestigated. Soil nutrient availability may shift the outcome of microbial interactions within a host individual or influence the pool of microbes across the plant community. We hypothesized that leaf microbial diversity would increase across the season as leaves collect additional taxa, and that this seasonal assembly would be sensitive to nutrient addition. To assess this, we tracked the assembly of the fungal phyllosphere microbiome of the grass tall fescue (Lolium arundinaceum) in old-field vegetation over the growing season and experimentally tested whether the seasonality of the microbiome was modified by experimental addition of soil nutrients. Fungal diversity (Shannon diversity index, richness, and evenness) increased early in the season, with most metrics saturating before the end of the season. Community composition as measured by Bray-Curtis dissimilarity also shifted over the early and mid-growing season. Phylogeny-based machine-learning identified fungal lineages that were abundant in different seasons, linking seasonal community shifts to their evolutionary context. Nutrient addition was less important than time of season, but still significantly altered community composition and interacted with time to influence richness, with lowest richness in the low nutrient addition plots early in the season. The clear seasonality of the microbiome provides support for a dynamic phyllosphere microbiome, suggesting further studies manipulating fungal recruitment over the season. Furthermore, it highlights the robustness of seasonal assembly to variation in nutrient availability.

Premise: Endophytic plant-microbe interactions range from mutualistic relationships that confer important ecological and agricultural traits to neutral or quasi-parasitic relationships. In contrast to root-associated endophytes, the role of environmental and host-related factors for acquiring leaf endophyte communities remains relatively unexplored. Here we assess leaf endophyte diversity to test the hypothesis that membership of these microbial communities is driven primarily by abiotic environment and host phylogeny. Methods: We used a broad geographic coverage of North America in the genus, Heuchera (Saxifragaceae). Bacterial and fungal communities were characterized with 16S and ITS amplicon sequencing, using QIIME2 to call operational taxonomic units and calculate species richness, Shannon diversity, and phylogenetic diversity. We assembled environmental predictors for microbial diversity at collection sites including latitude, elevation, temperature, precipitation, and soil parameters. Results: We find differing assembly patterns for bacterial and fungal endophytes; we found that only host phylogeny is significantly associated with bacteria, while geographic distance alone was the best predictor of fungal community composition. Species richness and phylogenetic diversity are very similar across sites and species, with only fungi showing a response to aridity and precipitation for some metrics. Unlike what has been observed with root-associated microbial communities, in this system microbes show no relationship with pH or other soil factors. Conclusions: Host phylogeny and geographic distance independently influence different microbial communities, while aridity and precipitation determine fungal diversity within leaves of Heuchera. Our results indicate the importance of detailed clade-based investigation of microbiomes and the complexity of microbiome assembly within specific plant organs.

AbstractEnhanced weathering (EW) of silicate minerals has emerged as a promising carbon dioxide removal (CDR) strategy, with potential benefits for soil fertility and crop performance. However, the soil processes that determine these co-benefits remain poorly constrained. In particular, interactions between basalt amendments and soil biota such as arbuscular mycorrhizal fungi (AMF) may influence nutrient mobilization and plant uptake, but these effects have rarely been quantified. In a 113-day mesocosm experiment with Zea mays using a Belgian, sandy loam soil, we investigated the effect of basalt and AMF inoculation on soil properties, nutrient and heavy metal availability, and crop yield and quality. We also assessed potential AMF-driven bio-weathering via cation mass balance and pore water dissolved inorganic carbon (DIC), pH, and alkalinity measurements. Basalt application, but not AMF, improved soil pH, cation exchange capacity, base saturation, and generally increased exchangeable Ca and Mg, whereas most other nutrients in the pore water remained unaffected. Crop yield and quality were largely unaltered by basalt or AMF, except for an increase in plant Mg with basalt application. Moreover, heavy metal availability and plant uptake were also generally unaffected, with the notable exception of soil pore water and corn Ni, which increased with basalt. These results suggest that risk for heavy metal contamination is not generic but may arise under specific environmental conditions. Finally, despite a synergistic effect of basalt and AMF on pore water DIC, we found no indication that AMF enhanced basalt weathering rates. Overall, AMF had limited influence on soil fertility indicators and crop performance. Basalt application improved key soil chemical indicators and increased the exchangeable fractions of Ca and Mg, demonstrating its role as a soil improver. Unlike several studies conducted in more acidic soils, these chemical enhancements did not increase maize growth here, indicating that the agronomic benefits of basalt are context-dependent.

O_LIAccounting for intraspecific variation may improve our understanding of species coexistence. However, our knowledge of what factors maintain intraspecific variation is limited. We predicted that 1) a plant grows larger when with non-kin (i.e. different genotypes) than kin (i.e. same genotype) neighbors, 2) abiotic stress alters the outcome of kin vs. non-kin interactions, 3) genetic identity of plants affects composition of soil microbiome. C_LIO_LIWe set up mini-communities of Medicago truncatula, where focal genotypes were grown together with two kin or two non-kin neighbors from different origins. We analyzed how origin, identity of interacting genotypes and abiotic stress affected growth and fruit production. We also analyzed the composition of soil microbial communities. C_LIO_LIFocal plants grew larger in non-kin than in kin mini-communities. This pattern was stronger in low level of abiotic stress and when interacting genotypes were from similar origins. However, genotypic variation in growth and response to competition had a stronger effect on growth than mini-community type. Plant genotype identity did not affect soil microbiome. C_LIO_LIWe find that intraspecific variation is affected by genotype-specific traits and abiotic stress. Geographic, rather than genetic, distance among interacting genotypes affects the outcome of intraspecific interactions. C_LI

O_LIDomestication has profoundly shaped the genetic makeup of numerous plant and animal species. While the effects of plant domestication at the genetic and phenotypic levels are well-documented, its impact on plant microbiome remains less understood. C_LIO_LITwo primary hypotheses have been proposed: 1) the reduction in microbial diversity resulting from the domestication process, and 2) the diminished ability of host plants to control their microbiomes. C_LIO_LIWe conducted a meta-analysis of multiple crops, comparing the root microbiomes of domesticated plants and their wild relatives. Our results indicate that the effects of domestication are species-specific and context-dependent, with most domesticated plants exhibiting increased microbial diversity and more structured communities. C_LIO_LIOverall, this study provides evidence that plant domestication does not lead to a uniform reduction in microbial diversity or a consistently diminished ability of plants to influence their microbiomes. C_LIO_LIBased on these findings, we discuss new perspectives and the need for future studies incorporating native soils and host genetic variation in such experiments, analyzing diversity and microbiome function, and considering how root morphology might affect microbiome recruitment. C_LI

O_LIPlants modulate their surrounding microbiome via root exudates and such conditioned soil microbiomes feed back on the performance of the next generation of plants. How plants perceive altered soil microbiomes and modulate their performance in response to such microbiome feedbacks however remains largely unknown. C_LIO_LIAs tool to condition contrasting microbiomes in soil, we made use of two maize lines, which differ in their ability to exude benzoxazinoids. Based on these differentially conditioned soil microbiomes we have established a model system with Arabidopsis thaliana (Arabidopsis) to investigate the mechanisms of microbiome feedbacks. C_LIO_LIArabidopsis plants responding to the benzoxazinoid-conditioned soil microbiome grew better and were developmentally more advanced. Further, these plants harboured differential root bacterial communities, showed enhanced defence signatures in transcriptomes of their shoots and they were more resistant to the fungal pathogen Botrytis cinerea. C_LIO_LIIntriguingly, Arabidopsis responded with both improved growth and enhanced defence to the benzoxazinoid-conditioned soil microbiome, and we found that this simultaneous increase of growth and defence was mediated by priming of the defences. Further advancing our basic understanding how plants respond to soil microbiomes and mediate their feedbacks is particularly important for the goal to improve crops so they can benefit from their soil microbiome. C_LI

O_LIMicrobial-based approaches have been proposed as a solution to decrease the use of chemical fertilizers in agriculture. Among these, the most promising candidates are arbuscular mycorrhizal fungi (AMF), with their ability to extend the root surface and absorb phosphate, and phosphate solubilizing bacteria (PSB), but their effectiveness has been shown to depend on plant genetic diversity. C_LIO_LIWith the aim of identifying genetic markers explaining plant differential responses to soil-beneficial microbes, we monitored a panel of 128 fully sequenced varieties of Lactuca sativa in a controlled condition of P starvation, treated with AMF and PSB. C_LIO_LIResults showed a strong effect of the lettuce genetic variation on the plant physiological and morphological response to the inoculum. Through genome-wide association studies (GWAS), we identified specific genetic regions associated with variations in leaf phosphate and shoot biomass in response to the treatment. Beyond genetic factors, root-associated microbes played a crucial role in shaping key plant nutritional parameters, with a change in fungal {beta}-diversity and an increase in bacterial -diversity associated with progressively higher leaf phosphate and shoot biomass response. C_LIO_LIIn conclusion, we highlighted key genetic and physiological mechanisms that could play a crucial role in enhancing microbial treatments for optimizing plant phosphate management. C_LI

BackgroundMicrobial communities in the rhizosphere are key drivers of plant immunity, mediating plant responses to stress. Under specific stresses plants are capable of recruiting beneficial microorganisms into their rhizosphere with the potential to alleviate these stresses. Among these stresses, herbivorous pests remain a major agricultural challenge. Despite this, the impact of leaf herbivory on root-associated microbiomes, and how this impact can shape plant defense phenotypes are still understudied. In this study, our main objective was to determine the extent to which leaf herbivory affects the rhizosphere microbiome, and whether and how these herbivory-induced changes modulate plant defense phenotypes through plant-soil feedback. To that end, we designed a two-phase assay in which we challenged sunflower (Helianthus annuus L.) with Spodoptera exigua and later tested the effect of the microbial legacy after infestation on sunflower defense phenotype, considering resistance and tolerance as major drivers. ResultsWe found that herbivory triggered significant changes in the bacteriome structure and dynamics, and microbiome functional profile, while effects on mycobiome were comparatively less pronounced. Under herbivory, several bacterial taxa and functional groups were enriched, the bacterial co-occurrence network was more complex and assembly processes were slightly more stochastic. Furthermore, after evaluating the plant-soil feedbacks of herbivory-induced microbiomes we observed no effect on plant resistance proxies such as herbivore growth and survival, and leaf phenolic and flavonoid content. We did observe differences on tolerance proxies, while plants grown on herbivore-challenged microbiome were overall smaller, the biomass loss to herbivory was significantly lower while the elemental nutrient content and photosynthetic pigments content was enhanced. ConclusionsOur study demonstrates that insect herbivory by S.exigua reshapes sunflower rhizosphere microbiome and generates a soil legacy that promotes herbivory tolerance on subsequent plant generations. This highlights the broader potential of microbiome-mediated plant-soil feedbacks in shaping plant adaptation to herbivory.

O_LIThere is growing interest in managing arbuscular mycorrhizal (AM) fungi in agriculture to support plant production. These fungi can support crop growth and nutrient uptake but also affect plant-herbivore interactions. Our knowledge of how native AM fungal diversity and community composition influence these interactions is limited, while our understanding of this in relation to root-herbivory is lacking altogether. C_LIO_LITo begin to address these knowledge gaps, plants were grown with no AM fungi or were inoculated with native fungal communities sourced from either a crop field (field community), a sclerophyll forest (forest community), or a crop field in fallow (fallow community). We then explored how the composition and structure (species richness and relative abundance) of root-colonising AM fungal communities was associated with the growth and belowground nutrient responses of a major crop (Sorghum bicolor) to attack from a root-feeding insect (Dermolepida albohirtum). C_LIO_LIDNA metabarcoding revealed plants associated with three distinct root-colonising AM fungal communities. Fungal taxon richness in roots was highest in the field community and lowest in the fallow community. Both the field and fallow communities were dominated by the putatively ruderal genera Glomus and Claroideoglomus, while the forest-derived community contained greater proportions of Paraglomus and Ambispora. C_LIO_LIIn response to root herbivory, plants without AM fungi and plants colonised by the forest community exhibited root biomass losses of 61% and 44%, respectively. Similarly, these two groups also had reductions of 59% and 65% in their root phosphorus content, respectively, when subjected to the root herbivore. In contrast, plants associating with communities harbouring greater proportions of Glomus and Claroideoglomus (the field and fallow communities) did not exhibit reductions in root biomass or nutrient content. C_LIO_LIOur results show that plant responses to root-herbivory vary with root-colonising AM fungal community composition and structure. In a community context, our findings suggest that stronger associations with the genera Claroideoglomus and Glomus may potentially support crop tolerance-associated responses belowground. There is an urgent need for more exploration of how natural assemblages of AM fungi differentially mediate plant-herbivore interactions if we are to effectively manage soil fungi in sustainable agricultural systems. C_LI

BackgroundThe assembly of tree microbiota is a dynamic process that varies across space and time, influenced by both biotic and abiotic factors. Plants have developed defence strategies, mediated by phytohormones such as ethylene, to manage its interactions with pathogens and, in certain non-perennials, interactions with the commensal microbiota. However, whether and how ethylene regulation affects the assembly of tree microbiota is unknown. ResultsWe investigated the assembly of fungal and bacterial communities in poplars (P. tremula x. P. tremuloides T89), altered either in ethylene biosynthesis (ACO1), or in ethylene perception (etr1.1), by combining high-throughput amplicon sequencing with confocal microscopy. In parallel, we characterised root exudates, as well as root and shoot metabolomes of the different poplar lines grown on sterile soil and in the presence of microbiota using GC-MS. Alteration of ethylene levels had little impact on the metabolome of sterile poplars, but led to differential primary and secondary metabolic responses in the root and shoots of poplars colonised by microorganisms. These metabolomic changes were associated with a decrease in fungal colonisation of shoots, particularly by saprophytes in the early stages, whereas reduced ethylene stimulated root colonisation by fungi. Conversely, arbuscular mycorrhizal fungal and bacterial communities, as well as root exudation, were little affected by changes in ethylene production. ConclusionThe findings of this study suggest a potential dual role for ethylene in poplar, whereby its levels may either promote or inhibit microbial growth and activity, depending on the concentration, microbial trophic guild, and poplar organ.

Plant-associated microbiomes play significant roles in determining their hosts responses to stress, which is increasingly common in a rapidly changing world. For example, foliar endophytes can increase tolerance to drought and decrease herbivory. Global atmospheric changes, such as increased atmospheric carbon dioxide concentration ([CO2]), have the potential to directly and indirectly alter microbiome community structure in ways that affect host plants underscoring our need to understand how microbial communities in planta will change under global change. Here, we used a metabarcoding approach to assess community composition and network structure of bacterial and fungal phyllosphere microbiomes within soybean (Glycine max) exposed to ambient and elevated [CO2] in the field. We found that fungal community composition differed between soybean grown in elevated and ambient [CO2], while bacterial communities did not. Additionally, co-occurrence networks for both fungi and bacteria in elevated [CO2] exhibited marked changes compared to the ambient networks including the composition of hub taxa. Overall, our findings suggest that anthropogenic change, such as elevated [CO2], can cause profound shifts in community assembly of microbes within their plant hosts. Our findings may aid those developing agro-ecological strategies using microbes to improve crop traits, which necessitates understanding the drivers of microbiome community structure. HighlightLeaf-associated microbes benefit plants, but how climate change affects these communities remains unclear. We found that elevated CO2 shifted fungal and bacterial community composition and network structure within soybean leaves.

O_LIMany agroecosystems face nitrogen (N), phosphorus (P) or potassium (K) deficiencies due to imbalanced or insufficient nutrient replenishment after plant biomass harvest. How this affects the symbiosis between plants and arbuscular mycorrhizal fungi (AMF), and the abundance of exploration-based AMF guilds (i.e., rhizophilic, edaphophilic, ancestral) remains largely unknown. C_LIO_LIWe studied a 70-year nutrient-deficiency experiment in a managed grassland in central Austria, where aboveground biomass was harvested three times annually. N, P and K were fully, partially, or not replenished, causing long-term nutrient deficiencies and imbalances. We analysed AMF communities in soil and roots by DNA/RNA amplicon sequencing and fatty-acid biomarkers, alongside soil and plant community properties. C_LIO_LISoil AMF communities were affected by N and P deficiencies, while root AMF communities were most susceptible to K deficiency, showing a 50% biomass reduction. We observed distinct guild- and family-specific responses: The edaphophilic guild declined with N deficiency, while the rhizophilic guild decreased with P and K deficiencies. Families within each guild, particularly in the ancestral guild, showed differential responses, indicating complementary nutrient specializations at the family level. C_LIO_LIOur findings underscore the previously unrecognized role of K deficiency in AMF symbiosis and suggest the existence of nutrient-related functional subgroups within exploration-based AMF guilds. C_LI

Background and aimsSoil microbiomes, critical for plant productivity and ecosystem functioning, mediate essential functions such as pathogenesis, mutualism, and decomposition through different fungal functional groups. Yet, our understanding of the dynamics of co-existing soil fungal functional groups in the plant rhizosphere remains limited. MethodsBy leveraging a natural experiment in urban farming with fields of different ages and multiple plant genotypes, we tracked the relative abundance, richness, and microbial networks of plant pathogens, mycorrhizal fungi, and saprotrophic fungi across fields over two years. ResultsWe observed an increase in the relative abundance of plant pathogens in older fields relative to younger fields, supporting the prediction of pathogen accumulation over time. In contrast, there was a decrease in the relative abundance of mycorrhizal fungi in older fields. Unlike plant pathogens and mycorrhizal fungi, the relative abundance of saprotrophic fungi remained similar among fields. While the richness of plant pathogens and saprotrophic fungi were similar across fields, the community structure of both groups differed between younger and older fields. For mycorrhizal fungi, the richness declined in older fields and over the two years. These dynamics led to distinct microbial networks, with decreased network links for mycorrhizal fungi and increased links for saprotrophic fungi in older fields, whereas the links for plant pathogens remained similar across fields. ConclusionOur study reveals contrasting dynamics of essential soil fungal functional groups in the plant rhizosphere, and provides a predictive insight into the potential shifts in soil function and their impact on plant productivity.

Arbuscular mycorrhizal fungi (AMF) have the potential to increase crop yields and all globally important crops form the mycorrhizal symbiosis. Only a few studies have investigated the impact of introduced AMF on local AMF communities and most studies have only investigated effects of one isolate. We studied the impact on AMF community structure of inoculating roots of the globally important crop cassava with highly genetically-related clonal siblings of two genetically different Rhizophagus irregularis isolates. We hypothesized that inoculation with R. irregularis siblings differentially influences the structure and the diversity of the pre-existing AMF community colonizing cassava. Alpha and beta taxonomic and phylogenetic AMF diversity were strongly and significantly altered differentially following inoculation with sibling AMF progeny. In most cases, the effects were also cassava-genotype specific. Although biomass production and AMF colonization were also both differentially affected by inoculation with sibling R. irregularis progeny these variables were not correlated with changes in the AMF community structure. The results highlight that investigations on the impact of an introduced AMF species, that use only one isolate, are unlikely to be representative of the overall effects of that AMF species and that the genetic identity of the host must be considered. The amount of inoculum added was very small and effects were observed 12 months following inoculation. That such a small amount of almost genetically identical fungal inoculum can strongly differentially influence AMF community structure 12 months following inoculation, indicates that AMF communities in tropical soils are not very resistant to perturbation.

Soil-dwelling bacteria and fungi play a crucial role in plant health and productivity by engaging in complex interactions that shape and are shaped by soil physico-chemical properties. In this study, we employed a multi-omics approach to investigate how variations in soil composition affect the grapevine holobiont. Grape plantlets were grown in three distinct soil types, namely sand, peat, and peat-manure. To further assess how variation in soil and root conditions affects the holobionts response, we included treatments involving soil autoclaving and root surface sterilisation across all soil types. We found that soil type significantly influences leaf multielement composition and concentration, while also shaping the bacterial and fungal communities associated with the plant rhizosphere. This shift led to changes in taxa involved in nitrogen fixation, biocontrol, and pathogenicity. Autoclaving soils consistently reduced bacterial diversity across all soil types, whereas fungal communities were less affected. In contrast, thermal treatment of roots had only a minor impact on microbial community composition but did induce transcriptional changes in the root and altered leaf macronutrient concentrations. Our findings indicate that differences in soil composition reshape the entire root-soil continuum, ultimately affecting plant physiology at multiple levels--from root function to leaf nutrient status. This highlights that the soil is not a passive growth medium but a key determinant of grape holobiont structure and function. These results reinforce the view that plant health and adaptation arise from integrated, dynamic interactions among the host, its associated microbiome, and the surrounding soil matrix.

Mucoromycotina fine root endophyte (M-FRE), although commonly present in cultivated crops, represent a largely overlooked symbiosis, and their diversity and ecological functions under natural field conditions remain poorly understood. The co-occurrence of M-FRE and Glomeromycotina arbuscular mycorrhizal fungi (G-AMF) was assessed in field-grown durum wheat (Triticum turgidum subsp. durum (Desf.) Husn.), testing the effects of combined water and nitrogen limitation on root colonization and fungal community diversity in roots, rhizosphere, and extra-radical hyphae. The M-FRE colonization was reduced under combined water and nitrogen stress but was unaffected by wheat genotype. In contrast, G-AMF colonization varied among genotypes and was insensitive to this combined stress. While G-AMF colonization correlated with root traits, M-FRE abundance was rather determined by soil properties and the applied stress. Remarkably, under stress, M-FRE but not G-AMF colonization correlated with nitrogen and phosphorus uptake in plant shoots. Partial 18S metabarcoding detected 74 G-AMF taxa and 12 M-FRE taxa, some shared across compartments, revealing active growth of M-FRE extra-radical hyphae. Stress had contrasting effects on diversity: G-AMF alpha diversity remained stable, whereas M-FRE diversity declined, with stress driving distinct community structures for both groups. These results indicate that M-FRE and G-AMF are shaped by divergent drivers, highlighting functional differences between these morphologically similar symbioses.

Across diverse ecosystems, bacteria and their host organisms engage in complex relationships having negative, neutral, or positive interactions. However, the specific effects of leaf- associated bacterial community functions on plant growth are poorly understood. To address this gap, we explored the relationships between bacterial community function and host plant growth in the purple pitcher plant (Sarracenia purpurea). The main aim of our research was to investigate how different bacterial community functions affect the growth and nutrient content in the plant. Previous research had suggested that microbial communities may aid in prey decomposition and subsequent nutrient acquisition in carnivorous plants, including S. purpurea. However, the specific functional roles of these bacterial communities in plant growth and nutrient uptake are not well known. In this study, sterile, freshly opened leaves (pitchers) were inoculated with three functionally distinct, pre-assembled bacterial communities and effects examined over 8 weeks. Bacterial community composition and function were measured using physiological assays, metagenomics, and metatranscriptomics. Distinct bacterial functions affected plant traits; a bacterial community enriched in decomposition and secondary metabolite production traits was associated with larger leaves with almost double the biomass of control pitchers. Physiological differences in bacterial communities were supported by metatranscriptomic analysis; for example, the bacterial community with the highest chitinase activity had greater expression of transcripts associated with chitinase enzymes. The relationship between bacterial community function and plant growth observed here indicates potential mechanisms for host-associated bacterial functions to support plant health and growth. ImportanceThis study addresses a gap in understanding the relationships between bacterial community function and plant growth. We inoculated sterile, freshly opened pitcher plant leaves with three functionally distinct bacterial communities to uncover potential mechanisms through which bacterial functions support plant health and growth. Our findings demonstrate that distinct bacterial functions significantly influence plant traits, with some bacterial communities supporting more growth than in control pitchers. These results highlight the ecological roles of microbial communities in plants and thus ecosystems, and suggest potential pathways in which microbes support host plant health. This research provides valuable insights into plant-microbe interactions and effects of diverse microbial community functions.