Mycorrhizal Growth Response Research Articles

Enhancing drought resistance in Pinus tabuliformis seedlings through root symbiotic fungi inoculation.

Drought constitutes a major abiotic stress factor adversely affecting plant growth and productivity. Plant-microbe symbiotic associations have evolved regulatory mechanisms to adapt to environmental stress conditions. However, the interactive effects of different fungi on host growth and stress tolerance under drought conditions remain unclear. This study explored the effects of varying polyethylene glycol (PEG-6000) concentrations (0%, 15%, 25%, and 35%) on the growth and physiological responses of two ectomycorrhizal fungi (Suillus granulatus (Sg) and Pisolithus tinctorius (Pt)) and two dark septate endophytes (Pleotrichocladium opacum (Po) and Pseudopyrenochaeta sp. (Ps)) isolated from the root system of Pinus tabuliformis. Specifically, the study aimed to evaluate six inoculation treatments, including no inoculation (CK), single inoculations with Sg, Pt, Po, Ps, and a mixed inoculation (Sg: Pt : Po: Ps = 1:1:1:1), on the growth and physiological characteristics of P. tabuliformis seedlings under different water regimes: well-watered at 70% ± 5%, light drought at 50% ± 5%, and severe drought at 30% ± 5% of the maximum field water holding capacity. All four fungi exhibited the capacity to cope with drought stress by enhancing antioxidant activities and regulating osmotic balance. Upon successful root colonization, they increased plant height, shoot biomass, root biomass, total biomass, and mycorrhizal growth response in P. tabuliformis seedlings. Under drought stress conditions, fungal inoculation improved seedling drought resistance by increasing superoxide dismutase and catalase activities, free proline and soluble protein contents, and promoting nitrogen and phosphorus uptake. Notably, mixed inoculation treatments significantly enhanced antioxidant capacity, osmotic adjustment, and nutrient acquisition abilities, leading to superior growth promotion effects under drought stress compared to single inoculation treatments. All four fungi tolerated PEG-induced drought stress, with increased antioxidant enzyme activities and osmotic adjustment substances and they promoted the growth and enhanced drought resistance of P. tabuliformis seedlings.

Is a combination of arbuscular mycorrhizal fungi more beneficial to enhance drought tolerance than single arbuscular mycorrhizal fungus in Lallemantia species?

Climate change-induced abiotic stress hinders crop growth, providing a challenge to global food security and agricultural sustainability. An effective approach to safeguard crop production from drought stress is to use either a single species or co-inoculating different native arbuscular mycorrhizal fungi (AMF) species. A pot experiment was carried out to examine the impacts of using single and combined AMF (Claroideoglomus etunicatum, Funneliformis mosseae, and Rhizophagus intraradices) on the growth and physiological-biochemical characteristics of Lallemantia species (Lallemantia iberica and L. royleana) under well-watered, moderate drought, and severe drought conditions. Drought stress had a notable negative impact on growth performance, photosynthetic rate, antioxidant enzyme activities, water use efficiency, nutrient uptake, oil and fatty acid levels, and sugar components, which were associated with restricted root development. In contrast, inoculation with mycorrhizal species, especially Mix 4 treatment (C. etunicatum, F. mosseae, and R. intraradices), significantly boosted root AMF colonization, leading to an increase in mycorrhizal growth response, mycorrhizal dependency, water use efficiency, and seed yield. Seeds produced under Mix 4 inoculation showed the highest levels of mucilage, sugar compounds, oil, and fatty acid compositions, compared with individual AMF and other AMF mixtures. Furthermore, the presence of hydrogen peroxide and lipid peroxidation was significantly reduced by applying Mix 4 treatment under drought stress. It suggested that a combination of AMF species can better promote the growth and yield of Lallemantia species during drought stress by preserving the plants' physiological functions than single arbuscular mycorrhizal fungus.

Domestication of rice may have changed its arbuscular mycorrhizal properties by modifying phosphorus nutrition-related traits and decreasing symbiotic compatibility.

Modern cultivated rice (Oryza sativa) typically experiences limited growth benefits from arbuscular mycorrhizal (AM) symbiosis. This could be due to the long-term domestication of rice under favorable phosphorus conditions. However, there is limited understanding of whether and how the rice domestication has modified AM properties. This study compared AM properties between a collection of wild (Oryza rufipogon) and domesticated rice genotypes and investigated the mechanisms underlying their differences by analyzing physiological, genomic, transcriptomic, and metabolomic traits critical for AM symbiosis. The results revealed significantly lower mycorrhizal growth responses and colonization intensity in domesticated rice compared to wild rice, and this change of AM properties may be associated with the domestication modifications of plant phosphorus utilization efficiency at physiological and genomic levels. Domestication also resulted in a decrease in the activity of the mycorrhizal phosphorus acquisition pathway, which may be attributed to reduced mycorrhizal compatibility of rice roots by enhancing defense responses like root lignification and reducing carbon supply to AM fungi. In conclusion, rice domestication may have changed its AM properties by modifying P nutrition-related traits and reducing symbiotic compatibility. This study offers new insights for improving AM properties in future rice breeding programs to enhance sustainable agricultural production.

The negative mycorrhizal growth response of host plants to Acaulospora cf. morrowiae irrespective of soil P availability

Acaulospora is one of the dominant genera of AMF associated with waterlogged vegetation, and its dominance was also revealed in the roots of a lowland rice variety indigenous to Southern Thailand. In a preliminary finding, the isolated Acaulospora showed growth suppression of lowland japonica Nipponbare rice, even in high phosphorus (P) soil. The isolated Acaulospora was identified to species level and assigned as Acaulospora cf. morrowiae Phattalung 1. The mycorrhizal growth response (MGR) of an upland indica rice and maize to A. cf. morrowiae was further tested under low and high P conditions. AMF colonization rates were high, over 70%, in both cases, with perfect arbuscule and vesicle formation; however, growth depression of the host plants was markedly observed. Reduced nutrient accumulation in both shoots and roots of host plants was noted, as depicted by nutrient profiling. To further substantiate the negative MGR to inoculation of A. cf. morrowiae, a standardized in vivo bioassay was performed using maize seedlings in a sand and perlite mixture, ensuring low P with 20 mg kg−1 P in the form of insoluble CaH2PO4. Shoot and root growth of maize seedlings were reduced at 23.7 and 36.1%, respectively, by the inoculation of AMF. The nutrient-parasitic nature of this AMF results from unproportioned drainage of photosynthates, indicating an unbalanced primary/nutrient trade-off system between symbionts. The overall associative merits or demerits of A. cf. morrowiae cannot be ruled out without thorough investigations considering several ecological perspectives and its fitter survival and dominance in waterlogged soils.

Short-term artificial adaptation of Rhizoglomus irregulare to high phosphate levels and its implications for fungal-plant interactions: phenotypic and transcriptomic insights.

Arbuscular mycorrhizal fungi (AMF) play a crucial role in enhancing plant growth, but their use in agriculture is limited due to several constraints. Elevated soil phosphate levels resulting from fertilization practices strongly inhibit fungal development and reduce mycorrhizal growth response. Here, we investigated the possibility of adapting Rhizoglomus irregulare to high phosphate (Pi) levels to improve its tolerance. A fungal inoculum was produced through multiple generations in the presence of elevated Pi and used to inoculate melon plants grown under low and high phosphate conditions. Our results revealed distinct phenotypic and transcriptomic profiles between the adapted and non-adapted Rhizoglomus irregulare. The Pi adapted phenotype led to enhanced root colonization under high Pi conditions, increased vesicle abundance, and higher plant biomass at both phosphate levels. Additionally, the adaptation status influenced the expression of several genes involved in Pi uptake, Pi signaling, and mitochondrial respiration in both symbiotic partners. While the underlying mechanisms of the adaptation process require further investigation, our study raises intriguing questions. Do naturally occurring phosphate-tolerant AMF already exist? How might the production and use of artificially produced inocula bias our understanding? Our findings shed light on the adaptive capacities of Glomeromycota and challenge previous models suggesting that plants control mycorrhizal fungal growth. Moreover, our work pave the way for the development of innovative biotechnological tools to enhance the efficacy of mycorrhizal inoculum products under practical conditions with high phosphate fertilization.

Shifts of arbuscular mycorrhizal fungal functioning along a simulated nitrogen deposition gradient

AbstractThe deposition of atmospheric nitrogen can significantly boost the amount of nitrogen available in various ecosystems, potentially altering the mutualistic association between arbuscular mycorrhizal fungi (AMF) and their host plants. Nevertheless, the precise mechanisms and the degree to which externally induced nitrogen‐related changes in AMF functionality might impact Sorghum bicolor (L.) Moench, a plant known for its high mycorrhizal colonization, remains unclear. In this study, the mycorrhizal response affected by environmental N enrichment was addressed by conducting a glasshouse experiment, and four fertilization treatments (N1, N2, N3, and N4, 0, 15, 30, and 60 kg N hm−1 a−1, respectively) were used to simulate N deposition differences over the mycorrhizal response. The changes in mycorrhizal colonization and plant variables during different AMF and N fertilizer applications were investigated. When the gradient's nitrogen levels increased, the mycorrhizal growth response and mycorrhizal nitrogen response showed a pattern of first dropping and then increasing. N‐induced changes in the mycorrhizal response were associated with vesicular colonization, arbuscular colonization, and root‐length colonization. The variation in the mycorrhizal response over the N concentration gradient highlights the critical role of AMF in agroecosystems.

The Effects of Rhizophagus irregularis Inoculation on Transcriptome of Medicago lupulina Leaves at Early Vegetative and Flowering Stages of Plant Development.

The study is aimed at revealing the effects of Rhizophagus irregularis inoculation on the transcriptome of Medicago lupulina leaves at the early (second leaf formation) and later (flowering) stages of plant development. A pot experiment was conducted under conditions of low phosphorus (P) level in the substrate. M. lupulina plants were characterized by high mycorrhizal growth response and mycorrhization parameters. Library sequencing was performed on the Illumina HiseqXTen platform. Significant changes in the expression of 4863 (padj < 0.01) genes from 34049 functionally annotated genes were shown by Massive Analysis of cDNA Ends (MACE-Seq). GO enrichment analysis using the Kolmogorov-Smirnov test was performed, and 244 functional GO groups were identified, including genes contributing to the development of effective AM symbiosis. The Mercator online tool was used to assign functional classes of differentially expressed genes (DEGs). The early stage was characterized by the presence of six functional classes that included only upregulated GO groups, such as genes of carbohydrate metabolism, cellular respiration, nutrient uptake, photosynthesis, protein biosynthesis, and solute transport. At the later stage (flowering), the number of stimulated GO groups was reduced to photosynthesis and protein biosynthesis. All DEGs of the GO:0016036 group were downregulated because AM plants had higher resistance to phosphate starvation. For the first time, the upregulation of genes encoding thioredoxin in AM plant leaves was shown. It was supposed to reduce ROS level and thus, consequently, enhance the mechanisms of antioxidant protection in M. lupulina plants under conditions of low phosphorus level. Taken together, the obtained results indicate genes that are the most important for the effective symbiosis with M. lupulina and might be engaged in other plant species.

Arbuscular mycorrhiza fungi Rhizophagus irregularis regulate iron and zinc homeostasis in tobacco by mediating the expression of Yellow Stripe-Like 7

Arbuscular mycorrhizal (AM) participate in fungi-plant symbiotic relationships and mediate the acquisition of soil-borne nutrients by host plants. However, little is known about how AM colonization affects the homeostasis of iron (Fe) and zinc (Zn) in the host plant. Here, we assessed the performance of mycorrhizal growth, oxidative defense, nutrient accumulation, and key gene responses in AM-colonized tobacco (Nicotiana tabacum L.) under different nutrient stress. The total mycorrhizal frequency of AM fungi on tobacco roots reached 86 % and 75 % under low and high phosphorus (P) treatments, respectively. Under Fe/Zn stress, AM alleviated the inhibition of tobacco biomass accumulation, decreased the content of lipid peroxides, and upregulated enzymatic antioxidant capability. In AM-colonized tobacco, Fe/Zn accumulation was increased under deficient conditions and decreased under surplus conditions. Tobacco uptake of P, Fe, and Zn was impaired by excess nutrient concentrations and improved at low concentrations, and this phenomenon was supported by AM colonization. Fe/Zn deficiency upregulated genes related to Fe/Zn uptake, and Fe/Zn excess upregulated genes related to heavy metal efflux, with AM colonization further promoting these upregulations. Notely, we found a possible crosstalk node, Yellow Stripe-Like 7 (NtYSL7), in the AM and Fe/Zn homeostasis regulatory network. NtYSL7 has a plasma membrane-localized oligopeptide transporter domain. NtYSL7 is strongly induced by AM colonization, deficiency of Fe, and surplus Zn, and interacts with many Fe/Zn transporters. AM assists host plants in maintaining Fe/Zn homeostasis by improving nutrient accumulation, redox homeostasis, and transport mechanisms, and NtYSL7 is likely important within the crosstalk network of AM, Fe, and Zn nutrient homeostasis.

Combined Phosphorus and Water stress Conditions Induce Negative Mycorrhizal Response in Maize (Zea mays L.)

Arbuscular mycorrhizal fungi (AMF) confer both positive and negative effects on the plant symbionts, depending on the prevailing growth condition. We investigated the effect of concurrent variations in phosphorus and soil moisture on percentage root colonization (%RC), mycorrhizal growth response (MGR) and drought response index (DRI) of SAMMAZ-16 maize variety in timescale. The experimental factors were AMF inoculation (addition or no addition), P2O5 applications (30, 60 or 90 kg ha-1) and water regimes (100% and 50% of the soil’s field capacity introduced after 4WAS). The result shows that the overall %RC was 62.22% at 8 weeks after sowing (WAS) and 71.33% at 12 WAS. With 30 and 60 kg P2O5 ha-1 application a rate, %RC was significantly higher at 12 WAS than that of similar application rates at 8 WAS. However, %RC was not different between 8 WAS and 12 WAS in 90 kg P2O5 ha-1 application. AMF inoculation tended to equilibrate the shoot growth of the inoculated plants to that of non- inoculated plants that received 50% higher doses of P2O5 under amply watered conditions. Increasing phosphorus application progressively alleviated the negative mycorrhizal response of the plants at the early stage of growth (week 4) and in 50% FC category at the other sampling times. Higher doses of P2O5 application improved the DRI of the maize in both samplings but the trend was more consistent in AMF-inoculated plants. We conclude that AMF inoculation would be detrimental to the growth of SAMMAZ-16 when there is combined phosphorus and water stress factors

Contrasting mycorrhizal growth responses in native and invasive woody species are associated with distinct root trait syndromes

Abstract Invasive plant species often express resource‐acquisitive leaf traits that support rapid growth, but associated fine root traits and the role of microbial mutualists in invader whole‐plant functioning remain poorly understood. We performed an experiment of 12 phylogenetically grouped native and non‐native, invasive woody species, grown with or without a common inoculum of arbuscular mycorrhizal fungi (AMF) across two nutrient levels. We measured 10 fine root traits associated with nutrient uptake and suitability of AMF colonization. The presence of AMF increased the growth rate of all species, but native species were significantly more dependent on AMF than invaders. Furthermore, invaders expressed a distinct syndrome of first‐order root traits, including longer, thinner roots of high specific root length, greater branching intensity and lower tissue density, which are traits associated with rapid nutrient uptake and low AMF association. This syndrome was independent of phylogeny, AMF inoculation and soil fertility. An acquisitive fine root trait syndrome for invaders supports high photosynthetic and growth rates, linking above‐ and below‐ground functioning. The occurrence of this syndrome across phylogenetic groups indicates that lineages of woody invaders typically associated with arbuscular mycorrhizas may be generally less dependent on AMF than native species. Read the free Plain Language Summary for this article on the Journal blog.

Micropropagated walnut dependency on phosphate fertilization and arbuscular mycorrhiza for growth, nutrition and quality differ between rootstocks both after acclimatization and post-acclimatization

The English walnut (Juglans regia L.) is the main species cultivated for the production of edible nuts. In vitro micropropagation of walnut explants, necessary for mass propagation of high-quality walnut rootstocks, needs an ex vitro acclimatization phase followed by a post-acclimatization growth in greenhouse when plantlets become photoautotrophic. However, poor survival and slow growth rates are common difficulties encountered in nurseries when establishing micropropagated walnut saplings. Walnut exhibits dependency on symbiotic soil-borne arbuscular mycorrhizal fungi for better soil nutrient acquisition and development due to a coarse root architecture that limits soil inorganic phosphate (Pi) uptake. In the context of rootstock production, the objective of this study was to investigate for the first time the effect of the arbuscular mycorrhizal fungus Rhizophagus irregularis on the growth, quality, and Pi nutrition of seven in vitro grown walnut rootstocks of economic interest (RG2, RG6, R17, RX1, VLACH, VX211, and WIP3). For this purpose, inoculation was performed before both acclimatization and post-acclimatization of rootstocks under two contrasting Pi fertilization regimes. Two months after inoculation, we analysed mycorrhizal growth, phosphate and quality responses in the four conditions tested by measuring plant height, root length, root surface, branch number, collar, biomass dry weight, Pi content, and quality (Dickson's index). The results indicated that Pi fertilization impacted root colonization parameters only in a few cases. Irrespective of root colonization parameters and developmental stages, mycorrhizal growth depression after inoculation with R. irregularis was generally observed with increasing Pi availability in the substrate. Principal component analysis showed that mycorrhizal dependency, growth and quality responses were positively correlated to each other under the lowest Pi fertilization regime tested, both at the acclimatization and post-acclimatization stages. We also found that mycorrhizal benefits in terms of growth, quality and Pi nutrition, were rootstock-dependent, indicating that walnut dependency for Pi nutrition varies between cultivars.

Arbuscular mycorrhiza alters the nutritional requirements in Salvia miltiorrhiza and low nitrogen enhances the mycorrhizal efficiency

Salvia miltiorrhiza Bunge (danshen in Chinese) is one of the most important medicinal cash crops in China. Previously, we showed that arbuscular mycorrhizal fungi (AMF) can promote S. miltiorrhiza growth and the accumulation of bioactive compounds. Fertilization may affect mycorrhizal efficiency, and appropriate doses of phosphate (P) and nitrogen (N) fertilizers are key factors for obtaining mycorrhizal benefits. However, the optimal fertilization amount for mycorrhizal S. miltiorrhiza remains unclear. In this study, we studied the effects of AMF on the growth and bioactive compounds of S. miltiorrhiza under different doses (low, medium, and high) of P and N fertilizer. The results showed that the mycorrhizal growth response (MGR) and mycorrhizal response of bioactive compounds (MBC) decreased gradually with increasing P addition. Application of a low (N25) dose of N fertilizer significantly increased the MGR of mycorrhizal S. miltiorrhiza, and a medium (N50) dose of N fertilizer significantly increased the MBC of phenolic acids, but decreased the MBC of tanshinones. Our results also showed that the existence of arbuscular mycorrhiza changes nutrient requirement pattern of S. miltiorrhiza. P is the limiting nutrient of non-mycorrhizal plants whereas N is the limiting nutrient of mycorrhizal plants.

Growth and nutrient uptake of haloxylon and atriplex as affected by mycorrhizal symbiosis under combined drought and salinity stresses

This study was conducted to determine the effect of arbuscular mycorrhizal fungi (AMF) symbiosis on plant growth and nutrient uptake under combined drought and salinity stresses. A pot experiment was carried out with a factorial arrangement of treatments in a completely randomized design with three replications. Experimental treatments included two plant types ( Atriplex canescens and Haloxylon ammodendron) with three levels of inoculation of fungal species ( Funneliformis geosporus, Funneliformis mosseae, and control), two levels of soil salinity stress (7 and 14 dS m–1), and two levels of drought stress (50% and 80% of management allowable depletion). Vegetative parameters, as well as root N, P, and K concentrations and uptakes, mycorrhizal growth response, mycorrhizal nitrogen response, mycorrhizal phosphorus response, mycorrhizal potassium response, and root colonization were measured. The results showed that the application of AMF increased the plant growth variables such as stem diameter, root length, shoot dry weights, and shoot to root ratio as well as nitrogen and phosphorus uptakes. The application of both AMF types was effective as compared to the control. However, F. mosseae indicated better performance especially, in terms of the effect on plant growth variables. Also, F. mosseae was more effective to relieve stress (i.e., salinity and drought) than F. geosporus. There was a significant difference between plant types and H. ammodendron had better efficiency than A. canescens under drought and salinity stresses. Based on the results, planting of H. ammodendron inoculated with F. mosseae might be recommended for soil conservation in the arid environments.

The Role of Medicago lupulina Interaction with Rhizophagus irregularis in the Determination of Root Metabolome at Early Stages of AM Symbiosis.

The nature of plant–fungi interaction at early stages of arbuscular mycorrhiza (AM) development is still a puzzling problem. To investigate the processes behind this interaction, we used the Medicago lupulina MlS-1 line that forms high-efficient AM symbiosis with Rhizophagus irregularis. AM fungus actively colonizes the root system of the host plant and contributes to the formation of effective AM as characterized by a high mycorrhizal growth response (MGR) in the host plant. The present study is aimed at distinguishing the alterations in the M. lupulina root metabolic profile as an indicative marker of effective symbiosis. We examined the root metabolome at the 14th and 24th day after sowing and inoculation (DAS) with low substrate phosphorus levels. A GS-MS analysis detected 316 metabolites. Results indicated that profiles of M. lupulina root metabolites differed from those in leaves previously detected. The roots contained fewer sugars and organic acids. Hence, compounds supporting the growth of mycorrhizal fungus (especially amino acids, specific lipids, and carbohydrates) accumulated, and their presence coincided with intensive development of AM structures. Mycorrhization determined the root metabolite profile to a greater extent than host plant development. The obtained data highlight the importance of active plant–fungi metabolic interaction at early stages of host plant development for the determination of symbiotic efficiency.

Impacts of aphid herbivory on mycorrhizal growth responses across three cultivars of wheat

Societal Impact StatementThe Earth's population is projected to rise to 9.7 billion by 2050 resulting in mounting pressure to increase agricultural yields in a sustainable manner. Arbuscular mycorrhizal (AM) fungi may be important players in this agricultural transition given their capacity to improve soil and plant health. Benefits gained by crops hosting AM fungi can be cultivar‐specific and also affected by insect herbivory, although the combined effect of these factors remains unclear. Here, we show that, in an economically and socially significant tri‐partite system, there is interplay between crop cultivar, AM colonisation and aphid herbivory on plant growth and nutritional status.Summary Arbuscular mycorrhizal (AM) fungi are critical components of the rhizosphere across nearly all terrestrial biomes. AM fungi associate with most plants, including major crops, usually increasing plant access to soil nutrients and enhancing defence against pests and pathogens in return for photosynthetic carbon (C). However, plant growth responses to AM fungi vary according to species and genotype, an issue pertinent in agro‐ecosystems where crop cultivar can play an important role in AM function. Evidence suggests other biotic interactions, including with sap‐feeding aphids, impact the function of AM symbioses in plants. Nonetheless, whether these biotic factors alter genotype (or cultivar)‐specific plant growth and nutritional responses to colonisation by AM fungi remains unclear. Here, we investigated whether mycorrhizal responsiveness of three cultivars of wheat (Triticum eastivum L.) to colonisation by a ubiquitously occurring AM fungus (Rhizophagus irregularis) differ in the presence or absence of bird cherry‐oat aphids (Rhopalosiphum padi), a major pest of cereals. Our findings show that although AM fungal colonisation and AM‐mediated plant growth responses were not affected by aphid feeding, there was variation between cultivars in the benefits gained by host plants in terms of nutrient acquisition and root growth, while aphid abundances also differed between wheat varieties. Understanding what causes cultivar‐specific outcomes and how they ultimately impact plant growth promotion, crop yields and food production represent key future research goals in agroecology.

Variation in mycorrhizal growth response among a spring wheat mapping population shows potential to breed for symbiotic benefit.

All cereal crops engage in arbuscular mycorrhizal symbioses which can have profound, but sometimes deleterious, effects on plant nutrient acquisition and growth. The mechanisms underlying variable mycorrhizal responsiveness in cereals are not well characterised or understood. Adapting crops to realise mycorrhizal benefits could reduce fertiliser requirements and improve crop nutrition where fertiliser is unavailable. We conducted a phenotype screen in wheat (Triticum aestivum L.), using 99 lines of an Avalon × Cadenza doubled‐haploid mapping population. Plants were grown with or without a mixed inoculum containing 5 species of arbuscular mycorrhizal fungi. Plant growth, nutrition and mycorrhizal colonisation were quantified. Plant growth response to inoculation was remarkably varied among lines, ranging from more than 30% decrease to 80% increase in shoot biomass. Mycorrhizal plants did not suffer decreasing shoot phosphorus concentration with increasing biomass as observed in their non‐mycorrhizal counterparts. The extent to which mycorrhizal inoculation was beneficial for individual lines was negatively correlated with shoot biomass in the non‐mycorrhizal state but was not correlated with the extent of mycorrhizal colonisation of roots. Highly variable mycorrhizal responsiveness among closely related wheat lines and the identification of several QTL for these traits suggests the potential to breed for improved crop‐mycorrhizal symbiosis.

A meta-analysis of the effects of climate change on the mutualism between plants and arbuscular mycorrhizal fungi.

Climate change and other anthropogenic activities have the potential to alter the dynamics of resource exchange in the mutualistic symbiosis between plants and mycorrhizal fungi, potentially altering its stability. Arbuscular mycorrhizal (AM) fungi, which interact with most plant species, are less cold‐tolerant than other groups of fungi; warming might therefore lead to increased fungal‐mediated nutrient transfers to plants, which could strengthen the mutualism. By stimulating photosynthesis, rising CO2 could reduce the carbon cost of supporting AM fungi, which may also strengthen the mutualism. Furthermore, rising temperature and CO2 could have stronger effects on the mutualism in wild plants than in domesticated plants because the process of domestication can reduce the dependence of plants on mycorrhizal fungi. We conducted a multi‐level random effects meta‐analysis of experiments that quantified the strength of the mutualism as plant growth response to AM fungal inoculation (i.e., mycorrhizal growth response) under contrasting temperature and CO2 treatments that spanned the Last Glacial Maximum (LGM) to those expected with future climate change. We tested predictions using a three‐level mixed effects meta‐regression model with temperature or CO2, domestication status and their interaction as moderators. Increases from subambient to ambient temperature stimulated mycorrhizal growth response only for wild, but not for domesticated plant species. An increase from ambient to superambient temperature stimulated mycorrhizal growth response in both wild and domesticated plants, but the overall temperature effect was not statistically significant. By contrast, increased CO2 concentration, either from subambient to ambient or ambient to super ambient levels, did not affect mycorrhizal growth response in wild or domesticated plants. These results suggest the mutualism between wild plants and AM fungi was likely strengthened as temperature rose from the past to the present and that forecasted warming due to climate change may have modest positive effects on the mutualistic responses of plants to AM fungi. Mutualistic benefits obtained by plants from AM fungi may not have been altered by atmospheric CO2 increases from the past to the present, nor are they likely to be affected by a forecasted CO2 increase. This meta‐analysis also identified gaps in the literature. In particular, (i) a large majority of studies that examined temperature effects on the mutualism focus on domesticated species (>80% of all trials) and (ii) very few studies examine how rising temperature and CO2, or other anthropogenic effects, interact to influence the mutualism. Therefore, to predict the stability of the mycorrhizal mutualism in the Anthropocene, future work should prioritize wild plant species as study subjects and focus on identifying how climate change factors and other human activities interact to affect plant responses to AM fungi.

Mycorrhizal and rhizobial interactions influence model grassland plant community structure and productivity.

Arbuscular mycorrhizal (AM) fungi and rhizobium are likely important drivers of plant coexistence and grassland productivity due to complementary roles in supplying limiting nutrients. However, the interactive effects of mycorrhizal and rhizobial associations on plant community productivity and competitive dynamics remain unclear. To address this, we conducted a greenhouse experiment to determine the influences of these key microbial functional groups on communities comprising three plant species by comparing plant communities grown with or without each symbiont. We also utilized N-fertilization and clipping treatments to explore potential shifts in mycorrhizal and rhizobial benefits across abiotic and biotic conditions. Our research suggests AM fungi and rhizobium co-inoculation was strongly facilitative for plant community productivity and legume (Medicago sativa) growth and nodulation. Plant competitiveness shifted in the presence of AM fungi and rhizobium, favoring M. sativa over a neighboring C4 grass (Andropogon gerardii) and C3 forb (Ratibida pinnata). This may be due to rhizobial symbiosis as well as the relatively greater mycorrhizal growth response of M. sativa, compared to the other model plants. Clipping and N-fertilization altered relative costs and benefits of both symbioses, presumably by altering host-plant nitrogen and carbon dynamics, leading to a relative decrease in mycorrhizal responsiveness and proportional biomass of M. sativa relative to the total biomass of the entire plant community, with a concomitant relative increase in A. gerardii and R. pinnata proportional biomass. Our results demonstrate a strong influence of both microbial symbioses on host-plant competitiveness and community dynamics across clipping and N-fertilization treatments, suggesting the symbiotic rhizosphere community is critical for legume establishment in grasslands.

The mycorrhizal-induced growth promotion and insect resistance reduction in Populus alba × P. berolinensis seedlings: a multi-omics study.

Arbuscular mycorrhizal (AM) fungi are an alternative to chemical insecticides or fertilizers, and there is an urgent need to extend the application of AM fungi to woody plants. This study aims to investigate the growth and resistance against the gypsy moth larvae (Lymantria dispar) in Glomus intraradices-colonized Populus alba × P. berolinensis seedlings, and to unravel the transcriptome and metabolome phenotypes recruited by AM fungus colonization that affect plant growth and insect resistance. Our results showed a positive mycorrhizal growth response, i.e., growth and biomass of mycorrhizal seedlings were enhanced. However, AM fungus inoculation reduced the resistance of poplar to gypsy moth larvae, as evidenced by the decreased carbon/nitrogen ratio in leaves, as well as the increased larval growth and shortened larval developmental duration. Transcriptome analysis revealed that in both auxin and gibberellin signaling transductions, all nodes were responsive to AM symbiosis and most differentially expressed genes belonging to effectors were up-regulated in mycorrhizal seedlings. Furthermore, the two key enzymes (4-coumarate-CoA ligase and trans-cinnamate 4-monooxygenase) involved in the synthesis of p-Coumaroyl-CoA, an initial metabolite in flavonoid biosynthesis and the first rate-limiting enzyme (chalcone synthase) in flavonoid biosynthesis, were down-regulated at the transcriptional level. Consistent with the transcriptome results, metabolome analysis found that the amounts of all differentially accumulated flavonoid compounds (e.g., catechin and quercetin) identified in mycorrhizal seedlings were decreased. Taken together, these findings highlight the diverse outcomes of AM fungi-host plant-insect interaction and reveal the regulatory network of the positive mycorrhizal growth response and mycorrhizal-induced reduction of insect resistance in poplar.

Growth responses of Sorghum bicolor (L.) Moench to arbuscular mycorrhizal fungi under simulated nitrogen deposition

Anthropogenic nitrogen (N) deposition leads to a dramatically increase in biologically available N in many ecosystems, which can change the symbiotic relationship between AMF and host plants. However, how and to what extent exogenous N-induced AMF could affect plants remains poorly understood. In this work, mycorrhizal growth responses of Sorghum bicolor to AMF under simulated N deposition were conducted in a glasshouse experiment. Results demonstrated that AMF elevated the growth performance and nutrient uptake (N, P) of S. bicolor at almost all treatments, although mycorrhizal colonization decreased with N addition. In addition, mycorrhizal response (MR) showed identical trend of first fall and then increase, and the lowest value was at the N1 treatment. The present study provided the first pot-based evidence that AMF can alleviate the mischief induced by high N addition, implying that AMF has a considerable significance in the farmland ecosystem under anthropogenic N deposition. Bangladesh J. Bot. 50(3): 933-938, 2021 (September) Special