Mycorrhizal Response Research Articles

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.

Arbuscular mycorrhizal fungi improve nutrient status of Commiphora myrrha seedlings under drought

In dryland ecosystems, tree and shrub seedling establishment, growth and survival are limited by access to water and nutrients. Arbuscular mycorrhizal fungi (AMF) increase seedling establishment and survival by enhancing nutrient and water acquisition. We executed a fully-factorial greenhouse experiment to determine the interactive effect of AMF (with and without), water deficit (four levels), and soil layer (topsoil and subsoil) on the biomass, growth, nutrient concentrations, and mycorrhizal root colonization of seedlings of Commiphora myrrha, a tree species that dominates large areas of dry forest and woodland in the Horn of Africa. Mycorrhizal seedlings had higher root and shoot biomass than non-mycorrhizal seedlings. They also had higher nutrient concentrations in root and shoot. Plant biomass was higher when plants were grown in topsoil at lower soil moisture levels. Mycorrhizal responsiveness was highest at lower soil moisture. The drought response index was higher for mycorrhizal than for non-mycorrhizal plants, indicating enhanced mycorrhizal benefits at lower water supply. Seedlings grew better in topsoil than in subsoil. Mycorrhizal colonization of roots of C. myrrha seedlings was higher with lower moisture and higher in topsoil than in subsoil. The increased performance of mycorrhizal C. myrrha indicates that mycorrhization is a major component of the adaptive strategy of seedlings of this species, similar to other species in these dryland deciduous ecosystems. We conclude that for restoration purposes with this species, nursery seedlings should be mycorrhized because of their enhanced growth performance.

Mycorrhizal responsiveness of modern hexaploid wheat and ancestral species under different soil fertility conditions

Mycorrhizal responsiveness of modern hexaploid wheat and ancestral species under different soil fertility conditions

The combined use of silicon and arbuscular mycorrhizas to mitigate salinity and drought stress in rice

Rice (Oryza sativa L.), being a high silicon (Si)-accumulator, is a major global food crop for more than half of the world's population. However, both salinity and drought, two of the most challenging abiotic stresses in rice-growing areas globally, threaten world food security. Both symbiosis with arbuscular mycorrhizal fungi (AMF) and supplementing paddy soils with Si have been shown to improve rice growth during drought and salinity-stress. However, their combined impact is poorly understood. AMF may absorb Si through their spores and hyphae and thus help accumulate root Si. In turn, Si can affect mycorrhizal responsiveness but the underlying mechanisms remain largely unknown. This review explores (i) how Si and AMF act to mitigate salinity and drought stress in rice plants and (ii) how they can be applied together. We also identify areas for future study and discuss how the combined presence of arbuscular mycorrhizas (AMs) and Si in paddy soils can generate more sustainable rice productivity.

The pivotal role of cultivar affinity to arbuscular mycorrhizal fungi in determining mycorrhizal responsiveness to water deficit

Arbuscular mycorrhizal fungi (AMF) have gained remarkable importance, having been proved to alleviate drought stress-induced damage in wheat due to their ability to ameliorate plant water use efficiency and antioxidant enzyme activity. However, despite the current relevance of the topic, the molecular and physiological processes at the base of this symbiosis never consider the single cultivar affinity to mycorrhization as an influencing factor for the metabolic response in the AMF-colonized plant. In the present study, the mycorrhizal affinity of two durum wheat species (T. turgidum subsp. durum (Desf.)) varieties, Iride and Ramirez, were investigated. Successively, an untargeted metabolomics approach has been used to study the fungal contribution to mitigating water deficit in both varieties. Iride and Ramirez exhibited a high and low level of mycorrhizal symbiosis, respectively; resulting in a more remarkable alteration of metabolic pathways in the most colonised variety under water deficit conditions. However, the analysis highlighted the contribution of AMF to mitigating water deficiency in both varieties, resulting in the up- and down-regulation of many amino acids, alkaloids, phenylpropanoids, lipids, and hormones.

Mycorrhizal fungi reduce fitness differences, but coexistence is determined by differences in intrinsic plant mycorrhizal responsiveness

AbstractPlant–arbuscular mycorrhizal fungal (AMF) associations can mediate soil resources among competing plants to influence plant resource capture and fitness, making AMF a potential agent of plant coexistence. We assessed plant coexistence, via niche and fitness differences, using six plant species varying in their mycorrhizal status. We grew the species in 15 competitive pairs with or without AMF. Effects of AMF on coexistence were determined by parametrizing pair-wise Lotka–Volterra plant competition models. Responses of the six plant species to AMF were determined by comparing the shoot biomass of single plants grown in the absence of any competition with AMF to the shoot biomass without AMF. The inoculation with AMF reduced the fitness differences between competitors, but the degree of AMF-mediated coexistence depended on the identity of the competing plant species. A greater AMF response difference between competing plant species reduced niche overlap and increased coexistence. These results show that while AMF generally reduce fitness differences, the equalizing effect of AMF is not always strong enough to overcome a competitive imbalance due to niche overlap and thus does not always lead to coexistence. Instead, it is the intrinsic growth response of different plant species to AMF, which can predict reduced niche overlap that in turn leads to coexistence. This implies that mycorrhizal dependence is a plant strategy to reduce niche overlap with competitors, thus allowing for greater coexistence.

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.

Evidence for the evolution of native plant response to mycorrhizal fungi in post-agricultural grasslands.

Plant–microbe interactions play an important role in structuring plant communities. Arbuscular mycorrhizal fungi (AMF) are particularly important. Nonetheless, increasing anthropogenic disturbance will lead to novel plant–AMF interactions, altering longstanding co‐evolutionary trajectories between plants and their associated AMF. Although emerging work shows that plant–AMF response can evolve over relatively short time scales due to anthropogenic change, little work has evaluated how plant AMF response specificity may evolve due to novel plant–mycorrhizal interactions. Here, we examine changes in plant–AMF interactions in novel grassland systems by comparing the mycorrhizal response of plant populations from unplowed native prairies with populations from post‐agricultural grasslands to inoculation with both native prairie AMF and non‐native novel AMF. Across four plant species, we find support for evolution of differential responses to mycorrhizal inocula types, that is, mycorrhizal response specificity, consistent with expectations of local adaptation, with plants from native populations responding most to native AMF and plants from post‐agricultural populations responding most to non‐native AMF. We also find evidence of evolution of mycorrhizal response in two of the four plant species, as overall responsiveness to AMF changed from native to post‐agricultural populations. Finally, across all four plant species, roots from native prairie populations had lower levels of mycorrhizal colonization than those of post‐agricultural populations. Our results report on one of the first multispecies assessment of local adaptation to AMF. The consistency of the responses in our experiment among four species provides evidence that anthropogenic disturbance may have unintended impacts on native plant species' association with AMF, causing evolutionary change in the benefit native plant species gain from native symbioses.

Specific Plant Mycorrhizal Responses Are Linked to Mycorrhizal Fungal Species Interactions.

Effects of arbuscular mycorrhizal fungi (AMF) on plants span the continuum from mutualism to parasitism due to the plant–AMF specificity, which obscures the utilization of AMF in the restoration of degraded lands. Caragana korshinskii, Hedysarum laeve, Caragana microphylla, and Poa annua are the most frequently used plants for revegetation in Kubuqi Desert, China, and the influence of AMF on their re-establishment remains to be explored further. Herein, using a greenhouse experiment, we tested the plant–AMF feedbacks between the four plant species and their conspecific or heterospecific AMF, retrieved from their rhizosphere in the Kubuqi Desert. AMF showed beneficial effects on plant growth for all these plant-AMF pairs. Generally, AMF increased the biomass of C. korshinskii, H. laeve, C. microphylla, and P. annua by 97.6, 50.6, 46.5, and 381.1%, respectively, relative to control. In addition, the AMF-plant specificity was detected. P. annua grew best, but C. microphylla grew worst with conspecific AMF communities. AMF community from P. annua showed the largest beneficial effect on all the plants (with biomass increased by 63.9–734.4%), while the AMF community from C. microphylla showed the least beneficial effect on all the plants (with biomass increased by 9.9–59.1%), except for P. annua (a 292.4% increase in biomass). The magnitude of AMF effects on plant growth was negatively correlated with the complexity of the corresponding AMF co-occurrence networks. Overall, this study suggests that AMF effects on plant growth vary due to plant-AMF specificity. We also observed the broad-spectrum benefits of the native AMF from P. annua, which indicates its potential utilization in the restoration of the desert vegetation.

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.

Microbial mediators of plant community response to long-term N and P fertilization: Evidence of a role of plant responsiveness to mycorrhizal fungi.

Climate changes and anthropogenic nutrient enrichment widely threaten plant diversity and ecosystem functions. Understanding the mechanisms governing plant species turnover across nutrient gradients is crucial to developing successful management and restoration strategies. We tested whether and how soil microbes, particularly arbuscular mycorrhizal fungi (AMF), could mediate plant community response to a 15years long-term N (0, 4, 8, and 16g N m-2 year-1 ) and P (0 and 8g N m-2 year-1 ) enrichment in a grassland system. We found N and P enrichment resulted in plant community diversity decrease and composition change, in which perennial C4 graminoids were dramatically reduced while annuals and perennial forbs increased. Metabarcoding analysis of soil fungal community showed that N and P changed fungal diversity and composition, of which only a cluster of AMF identified by the co-occurrence networks analysis was highly sensitive to P treatments and was negatively correlated with shifts in percentage cover of perennial C4 graminoids. Moreover, by estimating the mycorrhizal responsiveness (MR) of 41 plant species in the field experiment from 264 independent tests, we found that the community weighted mean MR of the plant community was substantially reduced with nutrient enrichment and was positively correlated with C4 graminoids percentage cover. Both analyses of covariance and structural equation modeling indicated that the shift in MR rather than AMF composition change was the primary predictor of the decline in perennial C4 graminoids, suggesting that the energy cost invested by C4 plants on those sensitive AMF might drive the inferior competitive abilities compared with other groups. Our results suggest that shifts in the competitive ability of mycorrhizal responsive plants can drive plant community change to anthropogenic eutrophication, suggesting a functional benefit of mycorrhizal mutualism in ecological restoration following climatic or anthropogenic degradation of soil communities.

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.

Breeding Practice Improves the Mycorrhizal Responsiveness of Cotton (Gossypium spp. L.).

Maximizing the function of indigenous arbuscular mycorrhizal (AM) fungi by choosing specific crop genotypes offers one of the few untapped opportunities to improve the sustainability of agriculture. In this study, the differences in mycorrhizal responsiveness (MR) in plant growth and shoot phosphorus (P) content among cotton (Gossypium spp. L.) genotypes from different release dates were compared and then the relationships between MR and P uptake-related traits were determined. The experimental design in a greenhouse included 24 genotypes released from 1950 to present in Xinjiang Province, inoculation with or without AM fungi, and P levels (15 and 150 mg P kg–1 added as KH2PO4). Results showed that the modern cotton genotypes exhibited a higher degree of mycorrhizal colonization, the hyphal length density (HLD), and mycorrhizae-induced changes in shoot growth than the old genotypes when inoculated with indigenous AM fungi at both the P levels. Moreover, MR was highly correlated with the HLD at low P levels and the HLD may provide useful insights for future cotton breeding aimed at delivering crop genotypes that can benefit more from AM fungi.

Arbuscular mycorrhizal fungal response to fire and urbanization in the Great Smoky Mountains National Park

Wildfires are increasing in frequency and intensity as drier and warmer climates increase plant detrital fuel loads. At the same time, increases in urbanization position 9% of fire-prone land within the United States at the wildland–urban interface. While rarely studied, the compounded effects of urbanization and wildfires may have unknown synergistically negative effects on ecosystems. Previous studies at the wildland–urban interface often focus on aboveground plant communities, but belowground ecosystems may also be affected by this double disturbance. In particular, it is unclear how much fire and urbanization independently or interactively affect nutritional symbioses such as those between arbuscular mycorrhizal (AM) fungi and the majority of terrestrial plants. In November 2016, extreme drought conditions and long-term fire suppression combined to create a wildfire within the Great Smoky Mountains National Park and the neighboring exurban city of Gatlinburg, TN. To understand how the double disturbance of urbanization and fire affected AM fungal communities, we collected fine roots from the 5 dominant understory species in September 2018 at each of 18 sites spanning 3 burn severities in both exurban and natural sites. Despite large variation in burn severity, plant species identity had the largest influence on AM fungi. AM fungal colonization, richness, and composition all varied most among plant species. Fire and urbanization did influence some AM fungal metrics; colonization was lower in burned sites and composition was more variable among exurban locations. There were no interactions among burn severity and urbanization on AM fungi. Our results point to the large influence of plant species identity structuring this obligate nutritional symbiosis regardless of disturbance regime. Therefore, the majority of AM fungal taxa may be buffered from fire-induced ecosystem changes if plant community composition largely remains intact, plant species life history traits allow for AM fungal persistence after fire disturbance, and/or nearby undisturbed habitat can act as an inoculum source for recolonization following fires. Thus, it is critical to maintain natural, undisturbed habitats interspersed within the wildland–urban interface.

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

Effects of Arbuscular Mycorrhizal Fungi on Rice Growth Under Different Flooding and Shading Regimes.

Arbuscular mycorrhizal fungi (AMF) are present in paddy fields, where they suffer from periodic soil flooding and sometimes shading stress, but their interaction with rice plants in these environments is not yet fully explained. Based on two greenhouse experiments, we examined rice-growth response to AMF under different flooding and/or shading regimes to survey the regulatory effects of flooding on the mycorrhizal responses of rice plants under different light conditions. AMF had positive or neutral effects on the growth and yields of both tested rice varieties under non-flooding conditions but suppressed them under all flooding and/or shading regimes, emphasizing the high importance of flooding and shading conditions in determining the mycorrhizal effects. Further analyses indicated that flooding and shading both reduced the AMF colonization and extraradical hyphal density (EHD), implying a possible reduction of carbon investment from rice to AMF. The expression profiles of mycorrhizal P pathway marker genes (GintPT and OsPT11) suggested the P delivery from AMF to rice roots under all flooding and shading conditions. Nevertheless, flooding and shading both decreased the mycorrhizal P benefit of rice plants, as indicated by the significant decrease of mycorrhizal P responses (MPRs), contributing to the negative mycorrhizal effects on rice production. The expression profiles of rice defense marker genes OsPR1 and OsPBZ1 suggested that regardless of mycorrhizal growth responses (MGRs), AMF colonization triggered the basal defense response, especially under shading conditions, implying the multifaceted functions of AMF symbiosis and their effects on rice performance. In conclusion, this study found that flooding and shading both modulated the outcome of AMF symbiosis for rice plants, partially by influencing the mycorrhizal P benefit. This finding has important implications for AMF application in rice production.

Mycorrhizal growth and phosphorus responses of tropical soybean (Glycine max L.) cultivars differ with arbuscular mycorrhizal fungi isolates and phosphorus application rates in a derived-savanna zone of Nigeria

Arbuscular mycorrhizal fungi (AMF) form symbiosis with most crops and provide a sustainable approach to promote crop productivity in phosphorus (P) deficient soils. There is scarcity of information on mycorrhizal growth and P responses in relation to different AMF isolates, P rates and soybean cultivars in Nigeria. Thus, field experiments were conducted for two consecutive years (2017 − 2018) to explore the impacts of different AMF isolates (Funneliformis mosseae, Rhizophagus intraradices and Claroideoglomus etunicatum) and P application rates (0, 20 and 40 kg P2O5 ha−1) on plant growth, mycorrhizal responses, nodulation, P nutrition and grain yield of two soybean cultivars (TGx 1448-2E and TGX 1440-1E). The results showed that mycorrhizal inoculation significantly enhanced root colonization, shoot biomass, nodulation, P uptake, P use efficiency and grain yield of the soybean cultivars compared to control. Inoculation of R. intraradices and F. mosseae consistently favored mycorrhizal responses compared to C. etunicatum. Application of high P rate (40 kg ha−1) negatively affected root colonization, mycorrhizal growth and P responses in inoculated plants. Both cultivars showed similar mycorrhizal responses. Mycorrhizal growth and P responses were significantly enhanced with inoculation of R. intraradices or F. mosseae and P rate of 20 kg ha−1, which resulted in increased P uptake, shoot biomass and grain yield in both cropping years . The findings indicated that inoculation of R. intraradices or F. mosseae with moderate P rate (20 kg ha−1) is optimal to promote plant growth, P nutrition and grain yield of tropical soybean for sustainable cultivation in Nigeria.

Native arbuscular mycorrhizal fungi respond to rehabilitation in iron ore mining areas from the Eastern Brazilian Amazon

Rehabilitation of mining areas is a relevant and current subject, in which the response of microbial communities is an important evaluation tool regarding their progress. In this context, our study had the objective of evaluating the effect of rehabilitation on the community composition and activity of arbuscular mycorrhizal fungi, and their relation with main soil properties, in three iron ore mining sites from Serra Norte of Carajás in the Eastern Brazilian Amazon. For that, non-rehabilitated, rehabilitated, and reference areas within each site were evaluated for spore density and diversity, mycorrhizal colonization, glomalin contents, as well as soil chemical and physical attributes. In general, all mycorrhizal variables responded positively to the rehabilitation processes in the three mining sites. Over time, an increase of similarity of the mycorrhizal communities between rehabilitated and reference areas from each site was observed, as well as, a decrease of the easily extractable glomalin/total extractable glomalin ratio. High ratios of easily extractable glomalin/total extractable glomalin indicated high degree of disturbance and/or disequilibrium of ecosystems, whereas low ratios indicated their equilibrium and/or recovery. This relation can be an interesting parameter, easy to interpret and compare for assessing the degree of disturbance, equilibrium and/or recovery of environments, regardless of absolute values of these variables. Main soil properties related to mycorrhizal response were pH, texture, organic matter content, and cation exchange capacity. Briefly, our results showed the resilience of native mycorrhizal communities and the success of the rehabilitation actions carried out in this Amazonian region.

Mycorrhizal growth and phosphorus responses of tomato differ with source but not application rate of phosphorus fertilisers

Phosphorus (P) can be added to the soil from various sources (e.g., chemical fertilisers and organic materials), and P fertilisation affects mycorrhizal colonisation and function in plants. While arbuscular mycorrhizal symbiosis is an integral part of most crop plants, there is a gap in understanding mycorrhizal growth and nutrition responses in relation to different sources of P at similar and variable application rates. Here we explore the impacts of different P sources (solely inorganic, mixed, or solely P-rich organic material), applied at three P application rates, on plant growth, nutrition and mycorrhizal responses. Tomato plants (arbuscular mycorrhizal and non-mycorrhizal plants) were grown in a soil amended with 10, 20 and 40 mg P kg−1. We found that the solely inorganic P source affected mycorrhizal and non-mycorrhizal plants differently to the solely P-rich organic source, as did the combination of the two, even with P application rates matched between different sources. The solely inorganic P source consistently favoured mycorrhizal plants, whereas mycorrhizal plants performed less successfully than non-mycorrhizal plants in the solely P-rich organic source. However, mycorrhizal and non-mycorrhizal plants responded equally in the soil where the mixed P source was added. The results indicated that blending inorganic and organic P sources could be used to mitigate negative effects of AMF on plant growth and P nutrition compared to using solely P-rich organic material.

Shading mediates the response of mycorrhizal maize (Zea mays L.) seedlings under varying levels of phosphorus

Arbuscular mycorrhizal fungi (AMF) form a beneficial symbiosis with most plant roots for the provision of phosphorus in exchange for plant carbohydrates, and the carbon-phosphorus relationship between AMF and host plant plays a key role in understanding the AM symbiosis. In agroecosystems, shading significantly affects the crop growth, however, it remains unclear how shading mediates the mycorrhizal response to phosphorus (P) supply. For this, a greenhouse experiment was conducted, and maize seedlings were subjected to shading and non-shading by means of leaves coverage under three P fertilization treatments, i.e., P15: 15 mg kg−1, P40: 40 mg kg−1, and P100: 100 mg kg−1. We used two AMF inocula for maize inoculation, i.e., Rhizophagus intraradices (R. intraradices) and Funneliformis mosseae (F. mosseae). We found that shading significantly decreased the soluble sugar concentration in phloem of mycorrhizal maize but not in the non-mycorrhizal ones. Root biomass and the root-shoot ratio of mycorrhizal maize decreased significantly under the shading treatment at P15, P40, and P100. The gene expression of ZmPht1;6 significantly decreased as the P supply level increased. Generally, shading and AM fungal species had no significant effect on the gene expression of ZmPht1;6. Mycorrhizal P response (MPR) decreased gradually as the P supply level increased. Sugar concentration in the phloem saps of inoculated maize was negatively correlated with the expression of ZmPht1;6 genes. Shading significantly increased the gene expression level of ZmPht1;6 inoculated with R. intraradices but had no effects with F. mosseae inoculation. However, the shoot and root MPR inoculated with F. mosseae were significantly higher than that inoculated with R. intraradices. Our findings demonstrate that shading mediates the carbon allocation of mycorrhizal maize seedlings, and the response is associated with P uptake systems, suggesting that tight linkages between aboveground carbon supply and P resource could play a role in maintaining mycorrhizal functioning in the agroecosystems.