Photosynthetic Traits and Nitrogen Uptake in Crops: Which Is the Role of Arbuscular Mycorrhizal Fungi?

Effects of Trichoderma harzianum and Bacillus subtilis on the root and soil microbiomes of the soybean plant INTACTA RR2 PRO™

Introduction

Soybean is a significant export product for several countries, including the United States and Brazil. There are numerous varieties of soybean. Among them, a genetically modified type known as INTACTA RR2 PRO™ has been designed to demonstrate resistance to glyphosate and to produce toxins that are lethal to several species of caterpillars. Limited information is available on the use of Trichoderma harzianum and Bacillus subtilis to promote plant growth and their impact on the plant microbiome.

Methods

This study aimed to evaluate the effects of these microorganisms on this soybean cultivar by analyzing parameters, such as root and shoot dry matter, nutritional status, and root and soil microbial diversity.

Results

The results indicated that treatments with B. subtilis alone or in combination with T. harzianum as seed or seed and soil applications significantly enhanced plant height and biomass compared to the other treatments and the control. No significant differences in phosphorus and nitrogen concentrations were detected across treatments, although some treatments showed close correlations with these nutrients. Microbial inoculations slightly influenced the soil and root microbiomes, with significant beta diversity differences between soil and root environments, but had a limited overall impact on community composition.

Discussion

The combined application of B. subtilis and T. harzianum particularly enhanced plant growth and promoted plant-associated microbial groups, such as Rhizobiaceae, optimizing plant-microbe interactions. Furthermore, the treatments resulted in a slight reduction in fungal richness and diversity.

Root symbiotic fungi improve nitrogen transfer and morpho-physiological performance in Chenopodium quinoa

Root-associated fungal endophytes may facilitate nitrogen (N) absorption in plants, leading to benefits in photosynthesis and growth. Here, we investigated whether endophytic insect pathogenic fungi (EIPF) are capable of transferring soil N to the crop species Chenopodium quinoa. We evaluated nutrient uptake, carbon allocation, and morpho-physiological performance in C. quinoa in symbiosis with two different EIPF (Beauveria and Metarhizium) under contrasting soil N supply. A controlled experiment was conducted using two plant groups: (1) plants subjected to low N level (5 mM urea) and (2) plants subjected to high N level (15 mM urea). Plants from each group were then inoculated with different EIPF strains, either Beauveria (EIPF1+), Metarhizium (EIPF2+) or without fungus (EIPF-). Differences in N and C content, amino acids, proteins, soluble sugars, starch, glutamine synthetase, glutamate dehydrogenase, and physiological (photosynthesis, stomatal conductance, transpiration), and morphological performance between plant groups under each treatment were examined. We found that both Beauveria and Metarhizium translocated N from the soil to the roots of C. quinoa, with positive effects on photosynthesis and plant growth. These effects, however, were differentially affected by fungal strain as well as by N level. Additionally, an improvement in root C and sugar content was observed in presence of EIPF, suggesting translocation of carbohydrates from leaves to roots. Whereas both strains were equally effective in N transfer to roots, Beauveria seemed to exert less demand in C. quinoa for photosynthesis-derived carbohydrates compared to Metarhizium. Our study revealed positive effects of EIPF on N transfer and morpho-physiological performance in crops, highlighting the potential of these fungi as an alternative to chemical fertilizers in agriculture systems.

Deciphering the impact of nitrogen morphologies distribution on nitrogen and biomass accumulation in tobacco plants

Background and aims

Nitrogen (N) distribution in plants is intricately linked to key physiological functions, including respiration, photosynthesis, structural development, and nitrogen storage. However, the specific effects of different N morphologies on N accumulation and plant growth are poorly understood. Our research specifically focused on determining how different N morphologies affect N absorption and biomass accumulation.

Methods

This study elucidated the impact of different application rates (CK: 0 g N/plant; T1: 4 g N/plant; T2: 8 g N/plant) of N fertilizer on N and biomass accumulation in tobacco cultivars Hongda and K326 at different growth stages.

Results

Our findings emphasize the critical role of N distribution in various plant parts, including leaves, stems, and roots, in determining the complex mechanisms of N and biomass accumulation in tobacco. We found that in relation to total N, a greater ratio of water-soluble N (N w) in leaves facilitated N accumulation in leaves. In contrast, an increased ratio of SDS (detergent)-insoluble N (N in-SDS) in leaves and non-protein N (N np) in roots hindered this increase. Additionally, our results indicate that a greater proportion of N np in leaves has a negative impact on biomass accumulation in leaves. Furthermore, elevated levels of N in-SDS, N w, and N np in roots, and N np in leaves adversely affected biomass accumulation in tobacco leaves. The Hongda cultivar exhibited greater biomass and N accumulation abilities as compared to K326.

Conclusions

Our findings highlight the significant role of distribution of N morphologies on plant growth, as well as N and biomass accumulation in tobacco plants. Understanding N distribution allows farmers to optimize N application, minimizing environmental losses and maximizing yield for specific cultivars. These insights advance sustainable agriculture by promoting efficient resource use and reducing environmental impact.

Arbuscular Mycorrhizal Fungi as Biostimulant and Biocontrol Agents: A Review

Arbuscular mycorrhizal fungi (AMF) are soil microorganisms living in symbiosis with most terrestrial plants. They are known to improve plant tolerance to numerous abiotic and biotic stresses through the systemic induction of resistance mechanisms. With the aim of developing more sustainable agriculture, reducing the use of chemical inputs is becoming a major concern. After providing an overview on AMF history, phylogeny, development cycle and symbiosis benefits, the current review aims to explore the potential of AMF as biostimulants and/or biocontrol agents. Nowadays, AMF inoculums are already increasingly used as biostimulants, improving mineral nutrient plant acquisition. However, their role as a promising tool in the biocontrol market, as an alternative to chemical phytosanitary products, is underexplored and underdiscussed. Thus, in the current review, we will address the mechanisms of mycorrhized plant resistance to biotic stresses induced by AMF, and highlight the various factors in favor of inoculum application, but also the challenges that remain to be overcome.

Effects of Funneliformis mosseae on Growth and Photosynthetic Characteristics of Camellia oleifera under Different Nitrogen Forms

Nitrogen fertilizer increases agricultural yields but increases economic costs and causes a series of environmental problems. Arbuscular mycorrhizal fungi (AMF) have the potential to be used as biological fertilizer. However, the influence of nitrogen form on plant growth responsiveness to AMF inoculation is poorly understood. In this study, we investigated the effects of Funneliformis mosseae on growth, root morphology and photosynthetic characteristics of Camellia oleifera under different nitrogen forms during three harvest periods and clarified the most suitable nitrogen form for C. oleifera-AMF symbiosis. The results showed that urea, ammonium and nitrate nitrogen promoted plant growth and photosynthetic capacity, among which urea treatment had the highest value in all three harvests. No significant difference in plant growth parameters was observed between ammonium and nitrate nitrogen treatments in the first two harvests, while the plant height was significantly lower under ammonium nitrogen treatment than nitrate nitrogen treatment in the third harvest. Inoculation with F. mosseae in the presence of indigenous AMF could promote AMF colonization and plant growth at all three harvest times. Inoculation with F. mosseae significantly increased gas exchange parameters, the maximum photochemical efficiency (Fv/Fm) and the actual photochemical efficiency (ΦPSII). Inoculation with AMF increased the photochemical quenching coefficient (qP) better under urea treatment and improved the non-photochemical quenching coefficient (qN) better under ammonium nitrogen treatment. Principal component analysis showed that urea is the most beneficial nitrogen fertilizer for C. oleifera-AMF symbiosis. The results of this study provide a theoretical basis for the combination use of AMF and nitrogen fertilizer in agroforestry.

A multi-organ maize metabolic model connects temperature stress with energy production and reducing power generation

Climate change has adversely affected maize productivity. Thereby, a holistic understanding of metabolic crosstalk among its organs is important to address this issue. Thus, we reconstructed the first multi-organ maize metabolic model, iZMA6517, and contextualized it with heat and cold stress transcriptomics data using expression distributed reaction flux measurement (EXTREAM) algorithm. Furthermore, implementing metabolic bottleneck analysis on contextualized models revealed differences between these stresses. While both stresses had reducing power bottlenecks, heat stress had additional energy generation bottlenecks. We also performed thermodynamic driving force analysis, revealing thermodynamics-reducing power-energy generation axis dictating the nature of temperature stress responses. Thus, a temperature-tolerant maize ideotype can be engineered by leveraging the proposed thermodynamics-reducing power-energy generation axis. We experimentally inoculated maize root with a beneficial mycorrhizal fungus, Rhizophagus irregularis, and as a proof-of-concept demonstrated its efficacy in alleviating temperature stress. Overall, this study will guide the engineering effort of temperature stress-tolerant maize ideotypes.

Enhancing alfalfa photosynthetic performance through arbuscular mycorrhizal fungi inoculation across varied phosphorus application levels

This study evaluated the effects of arbuscular mycorrhizal fungi inoculation on the growth and photosynthetic performance of alfalfa under different phosphorus application levels. This experiment adopts two-factors completely random design, and sets four levels of fungi application: single inoculation with Funneliformis mosseae (Fm, T1), single inoculation with Glomus etunicatum (Ge, T2) and mixed inoculation with Funneliformis mosseae × Glomus etunicatum (Fm×Ge, T3) and treatment uninfected fungus (CK, T0). Four phosphorus application levels were set under the fungi application level: P2O5 0 (P0), 50 (P1), 100 (P2) and 150 (P3) mg·kg-1. There were 16 treatments for fungus phosphorus interaction. The strain was placed 5 cm below the surface of the flowerpot soil, and the phosphate fertilizer was dissolved in water and applied at one time. The results showed that the intercellular CO2 concentration (Ci) of alfalfa decreased at first and then increased with the increase of phosphorus application, except for light use efficiency (LUE) and leaf instantaneous water use efficiency (WUE), other indicators showed the opposite trend. The effect of mixed inoculation (T3) was significantly better than that of non-inoculation (T0) (p < 0.05). Pearson correlation analysis showed that Ci was significantly negatively correlated with alfalfa leaf transpiration rate (Tr) and WUE (p < 0.05), and was extremely significantly negatively correlated with other indicators (p < 0.01). The other indexes were positively correlated (p < 0.05). This may be mainly because the factors affecting plant photosynthesis are non-stomatal factors. Through the comprehensive analysis of membership function, the indexes of alfalfa under different treatments were comprehensively ranked, and the top three were: T3P2>T3P1>T1P2. Therefore, when the phosphorus treatment was 100 mg·kg-1, the mixed inoculation of Funneliformis mosseae and Glomus etunicatum had the best effect, which was conducive to improving the photosynthetic efficiency of alfalfa, increasing the dry matter yield, and improving the economic benefits of local alfalfa in Xinjiang. In future studies, the anatomical structure and photosynthetic performance of alfalfa leaves and stems should be combined to clarify the synergistic mechanism of the anatomical structure and photosynthetic performance of alfalfa.

Metabolome profiling of arbuscular mycorrhizal fungus treated Ocimum tenuiflorum L. provides insights into deviation in allocation of carbon compounds to secondary metabolism

Arbuscular mycorrhiza (AM) has been reported to influence secondary metabolism of Ocimum tenuiflorum L., thereby improving its therapeutic and commercial importance. To explain changes in the secondary metabolite profile, the study reports effects of AM on leaf metabolome of two high yielding genotypes of O. tenuiflorum inoculated with Rhizophagus intraradices. NMR-based non-targeted metabolic fingerprinting was related to changes at physiological, biochemical, and molecular levels in mycorrhizal (M) plants. AM resulted in higher accumulation of sucrose, which could be related with enhanced photosynthesis by virtue of increased uptake of mineral nutrients. A strong positive correlation between sucrose and net photosynthetic rate and sucrose and mineral nutrients supported that AM-mediated increase in uptake of mineral nutrients is associated with enhanced photosynthetic rate and accumulation of sucrose. Further, higher sucrose synthase activity resulted in increased glucose. Hexokinase activity was also higher in M plants resulting in higher pyruvate accumulation. On the contrary, Krebs cycle was compromised in M plants as evident by lower activities of its enzymes and concentrations of organic and amino acids. Nevertheless, AM increased activities and expressions of enzymes of terpenoid biosynthesis, shikimate, and phenylpropanoid pathways, thereby resulting in augmented production of terpenoids, phenylalanine, and phenols, respectively. Thus, metabolic reprogramming downstream of glycolysis was apparent wherein AMF resulted in more allocation of carbon resources to secondary metabolism as opposed to primary metabolism, which was supported by Pearson's correlation analysis. Higher C:N ratio in M plants explains the provision of more carbon resources to secondary metabolism as against primary metabolism.

Formulation of Zinc oxide/Gum acacia nanocomposite as a novel slow-release fertilizer for enhancing Zn uptake and growth performance of Spinacia oleracea L

Zinc (Zn) deficiency has caused nutritional disorders in 17% of the world's population; thus, producing Zn-enriched plants as a dietary source is necessary. Recently, nanofertilizers have gained much attention as a substitute for conventional fertilizers; however, soil application of polymer-coated Zn-based nanofertilizer has not been explored much. The present study depicts the green synthesis of ZnO nanoparticles using Melia azedarach L. leaf extract, whose phytoconstituents have reducing abilities. The synthesized nanoparticles were combined with gum acacia (GA) to form a ZnOGA nanocomposite. The structural and morphological properties of ZnOGA were studied using XRD, FTIR, FESEM, and EDX. A pot experiment study was carried out with Spinacia oleracea L. at various doses (3, 5, and 10 mg/kg) of the synthesized ZnOGA to evaluate its effectiveness as a slow-release fertilizer and was compared with a commercial Zn fertilizer. The plant growth studies revealed a significant increase in the phyto-morphological traits of the plants fertilized with ZnOGA compared to commercial fertilizer. The plants also displayed significantly higher contents of protein (17-47%), phenols (25-60%), proline (82-94%), total soluble sugar (20-31%), DPPH activity (70-72%), and Zn uptake (91-106%). The doses of ZnOGA played an imperative role in determining the growth and productivity of the plant. Soil column studies showed that ZnOGA reduces Zn leaching by 52% compared to commercial Zn fertilizer. This study signifies the potential of ZnOGA to be applied as an eco-friendly and sustainable substitute for conventional Zn fertilizer minimizing Zn losses and Zn deficiency-related health problems in human populations.

Reduced Arbuscular Mycorrhizal Fungi (AMF) Diversity in Light and Moderate Fire Sites in Taiga Forests, Northeast China

Forest fires are an important disturbance factor in forest ecosystems, and obviously change the soil environment. Arbuscular mycorrhizal fungi, as a medium and bridge between vegetation and soil, play a crucial role in mediating plant nutrient uptake and regulating the productivity, stability, and succession of vegetation-soil systems. To investigate the effects of forest fires on the community structure and diversity of arbuscular mycorrhizal fungi in cold-temperate Larix gmelinii forests, we collected soils from light, moderate, and heavy fire disturbance forests and a natural forest as a control forest in Greater Khingan Larix gmelinii forests, in the northeast of China. The community structure and diversity of arbuscular mycorrhizal fungi was sequenced using Illumina MiSeq technology and we analyzed the correlation with the soil physicochemical characteristics. The results showed that the contents of microbial biomass content (MBC), moisture content (MC), total nitrogen (TN), and available phosphors (AP) increased significantly (p < 0.05) with increasing fire intensity (from Light to heavy fire), but available potassium (AK) decreased significantly (p < 0.05). These changes were not significant. A total of 14,554 valid sequences from all sequences were classified into 66 ASVs that belonged into one phylum, one order, four families, and four genera. The genera included Glomus, Ambispora, Paraglomus, and Acaulospora, and Glomus was the dominant genus (the genera with the five most relative abundances) in the control and heavy-fire forests. Non-metric multidimensional scaling (NMDS) analysis showed that forest fires significantly affected the community structure of arbuscular mycorrhizal fungi (p < 0.01). Redundancy analysis (RDA) showed that MBC, SOC, and AP contents significantly affected the composition structure and diversity of arbuscular mycorrhizal fungi communities. This study indicated that forest fires affected the composition and diversity of soil arbuscular mycorrhizal fungi communities through changing the soil physicochemical parameters (MBC, SOC, and AP) in cold-temperate Larix gmelinii forests. The study of soil physicochemical properties and arbuscular mycorrhizal fungi diversity in cold-temperate Larix gmelinii forests in the Greater Khingan Mountains after forest fires provides a reference basis for the revegetation and reconstruction of fire sites.

Mycorrhizal symbiosis alleviate salinity stress in pistachio plants by altering gene expression and antioxidant pathways

This study investigated how inoculation of salt-stressed Pistacia vera seedlings with Rhizophagus irregularis, an arbuscular mycorrhizal fungus (AMF), affects their biomass, oxidative damage, antioxidant enzyme activity, and gene expression. Pistachio seedlings (N:36) were randomly assigned to AMF inoculation and non-inoculation groups in a pot experiment with 9 replications. Each group was further divided and randomly assigned to two salinity treatments (0 and 300 mM NaCl). At the end of week 4, three pistachio plantlets were randomly selected from each group for Rhizophagus irregularis colonization inspection, physiological and biochemical assays, and biomass measurements. Salinity activated enzymatic and non-enzymatic antioxidant systems in the pistachio plants were studied. The negative effects of salinity included reduced biomass and relative water content (RWC), increased O2 ·-, H2O2, MDA, and electrolytic leakage. Generally, Rhizophagus irregularis was found to mitigate the adverse effects of salinity in pistachio seedlings. AMF inoculation resulted in even further increases in the activities of SODs, POD, CAT, and GR enzymes, upregulating Cu/Zn-SOD, Fe-SOD, Mn-SOD, and GR genes expression in plants under salinity stress. Moreover, AMF significantly increased AsA, α-tocopherol, and carotenoids under both control and salinity conditions. The study concludes with a call for future research into the mechanisms of mycorrhiza-induced tolerance in plants under salinity stress.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-023-01279-8.

Effects of arbuscular mycorrhizal fungi on plant growth and herbivore infestation depend on availability of soil water and nutrients

INTRODUCTION

Fitness of plants is affected by their symbiotic interactions with arbuscular mycorrhizal fungi (AMF), and such effects are highly dependent on the environmental context.

METHODS

In the current study, we inoculated the nursery shrub species Artemisia ordosica with AMF species Funneliformis mosseae under contrasting levels of soil water and nutrients (diammonium phosphate fertilization), to assess their effects on plant growth, physiology and natural infestation by herbivores.

RESULTS

Overall, plant biomass was synergistically enhanced by increasing soil water and soil nutrient levels. However, plant height was surprisingly repressed by AMF inoculation, but only under low water conditions. Similarly, plant biomass was also reduced by AMF but only under low water and nutrient conditions. Furthermore, AMF significantly reduced leaf phosphorus levels, that were strongly enhanced under high nutrient conditions, but had only minor effects on leaf chlorophyll and proline levels. Under low water and nutrient conditions, specific root length was enhanced, but average root diameter was decreased by AMF inoculation. The negative effects of AMF on plant growth at low water and nutrient levels may indicate that under these conditions AMF inoculation does not strongly contribute to nutrient and water acquisition. On the contrary, the AMF might have suppressed the direct pathway of water and nutrient absorption by the plant roots themselves despite low levels of mycorrhizal colonization. AMF inoculation reduced the abundance of the foliar herbivore Chrysolina aeruginosa on plants that had been grown on the low nutrient soil, but not on high nutrient soil. Fertilization enhanced the abundance of this herbivore but only in plants that had received the high water treatment. The lower abundance of the herbivore on AMF plants could be related to their decreased leaf P content. In conclusion, our results indicate that AMF negatively affect the growth of Artemisia ordosica but makes them less attractive to a dominant herbivore.

DISCUSSION

Our study highlights that plant responses to AMF depend not only on the environmental context, but that the direction of the responses can differ for different components of plant performance (growth vs. defense).

Unearthing soil-plant-microbiota crosstalk: Looking back to move forward

The soil is vital for life on Earth and its biodiversity. However, being a non-renewable and threatened resource, preserving soil quality is crucial to maintain a range of ecosystem services critical to ecological balances, food production and human health. In an agricultural context, soil quality is often perceived as the ability to support field production, and thus soil quality and fertility are strictly interconnected. The concept of, as well as the ways to assess, soil fertility has undergone big changes over the years. Crop performance has been historically used as an indicator for soil quality and fertility. Then, analysis of a range of physico-chemical parameters has been used to routinely assess soil quality. Today it is becoming evident that soil quality must be evaluated by combining parameters that refer both to the physico-chemical and the biological levels. However, it can be challenging to find adequate indexes for evaluating soil quality that are both predictive and easy to measure in situ. An ideal soil quality assessment method should be flexible, sensitive enough to detect changes in soil functions, management and climate, and should allow comparability among sites. In this review, we discuss the current status of soil quality indicators and existing databases of harmonized, open-access topsoil data. We also explore the connections between soil biotic and abiotic features and crop performance in an agricultural context. Finally, based on current knowledge and technical advancements, we argue that the use of plant health traits represents a powerful way to assess soil physico-chemical and biological properties. These plant health parameters can serve as proxies for different soil features that characterize soil quality both at the physico-chemical and at the microbiological level, including soil quality, fertility and composition of soil microbial communities.

Impacts of Biogas Slurry Fertilization on Arbuscular Mycorrhizal Fungal Communities in the Rhizospheric Soil of Poplar Plantations

The majority of terrestrial plants are symbiotic with arbuscular mycorrhizal fungi (AMF). Plants supply carbohydrates to microbes, whereas AMF provide plants with water and other necessary nutrients-most typically, phosphorus. Understanding the response of the AMF community structure to biogas slurry (BS) fertilization is of great significance for sustainable forest management. This study aimed to look into the effects of BS fertilization at different concentrations on AMF community structures in rhizospheric soil in poplar plantations. We found that different fertilization concentrations dramatically affected the diversity of AMF in the rhizospheric soil of the poplar plantations, and the treatment with a high BS concentration showed the highest Shannon diversity of AMF and OTU richness (Chao1). Further analyses revealed that Glomerales, as the predominant order, accounted for 36.2-42.7% of the AMF communities, and the relative abundance of Glomerales exhibited negligible changes with different BS fertilization concentrations, whereas the order Paraglomerales increased significantly in both the low- and high-concentration treatments in comparison with the control. Furthermore, the addition of BS drastically enhanced the relative abundance of the dominant genera, Glomus and Paraglomus. The application of BS could also distinguish the AMF community composition in the rhizospheric soil well. An RDA analysis indicated that the dominant genus Glomus was significantly positively correlated with nitrate reductase activity, while Paraglomus showed a significant positive correlation with available P. Overall, the findings suggest that adding BS fertilizer to poplar plantations can elevate the diversity of AMF communities in rhizospheric soil and the relative abundance of some critical genera that affect plant nutrient uptake.

Genotype, mycorrhizae, and herbivory interact to shape strawberry plant functional traits

Arbuscular mycorrhizal fungi (AMF) and herbivores are ubiquitous biotic agents affecting plant fitness. While individual effects of pairwise interactions have been well-studied, less is known about how species interactions above and belowground interact to influence phenotypic plasticity in plant functional traits, especially phytochemicals. We hypothesized that mycorrhizae would mitigate negative herbivore effects by enhancing plant physiology and reproductive traits. Furthermore, we expected genotypic variation would influence functional trait responses to these biotic agents. To test these hypotheses, we conducted a manipulative field-based experiment with three strawberry (Fragaria x ananassa) genotypes to evaluate plant phenotypic plasticity in multiple functional traits. We used a fully-crossed factorial design in which plants from each genotype were exposed to mycorrhizal inoculation, herbivory, and the combined factors to examine effects on plant growth, reproduction, and floral volatile organic compounds (VOCs). Genotype and herbivory were key determinants of phenotypic variation, especially for plant physiology, biomass allocation, and floral volatiles. Mycorrhizal inoculation increased total leaf area, but only in plants that received no herbivory, and also enhanced flower and fruit numbers across genotypes and herbivory treatments. Total fruit biomass increased for one genotype, with up to 30-40% higher overall yield depending on herbivory. Herbivory altered floral volatile profiles and increased total terpenoid emissions. The effects of biotic treatments, however, were less important than the overall influence of genotype on floral volatile composition and emissions. This study demonstrates how genotypic variation affects plant phenotypic plasticity to herbivory and mycorrhizae, playing a key role in shaping physiological and phytochemical traits that directly and indirectly influence productivity.

Molecular and Physiological Mechanisms to Mitigate Abiotic Stress Conditions in Plants

Agriculture production faces many abiotic stresses, mainly drought, salinity, low and high temperature. These abiotic stresses inhibit plants' genetic potential, which is the cause of huge reduction in crop productivity, decrease potent yields for important crop plants by more than 50% and imbalance agriculture's sustainability. They lead to changes in the physio-morphological, molecular, and biochemical nature of the plants and change plants' regular metabolism, which makes them a leading cause of losses in crop productivity. These changes in plant systems also help to mitigate abiotic stress conditions. To initiate the signal during stress conditions, sensor molecules of the plant perceive the stress signal from the outside and commence a signaling cascade to send a message and stimulate nuclear transcription factors to provoke specific gene expression. To mitigate the abiotic stress, plants contain several methods of avoidance, adaption, and acclimation. In addition to these, to manage stress conditions, plants possess several tolerance mechanisms which involve ion transporters, osmoprotectants, proteins, and other factors associated with transcriptional control, and signaling cascades are stimulated to offset abiotic stress-associated biochemical and molecular changes. Plant growth and survival depends on the ability to respond to the stress stimulus, produce the signal, and start suitable biochemical and physiological changes. Various important factors, such as the biochemical, physiological, and molecular mechanisms of plants, including the use of microbiomes and nanotechnology to combat abiotic stresses, are highlighted in this article.

Host plant richness and environment in tropical forest transformation systems shape arbuscular mycorrhizal fungal richness

Transformation of tropical lowland rain forests into rubber tree and oil palm plantations is the cause of massive loss of vegetation diversity. The consequences for associated mycorrhizal fungi are not fully understood. We hypothesized that generalist arbuscular mycorrhizal fungi are resistant to removal of host species richness and that forest conversion to oil palm and rubber leads to loss of arbuscular mycorrhizal fungal (AMF) species with host preferences. Plant identities and AMF species were determined by molecular barcoding of 112 roots collected in three land-use systems (rain forest, rubber tree and oil palm plantation) in two landscapes on Sumatra (Indonesia), a world hotspot of forest transformation. The collected roots were from 43 forest plant species, in addition to rubber trees and oil palms. We detected 28 AMF species of which about 75% were present in forest trees and 25% shared among the land use systems. Only one AMF species present in plantation roots was not detected in the analyzed forest roots. Host specificity of arbuscular mycorrhizal fungi was not detected. Oil palm and rubber tree roots exhibited a strong reduction in AMF richness compared with roots from rainforests and were differentiated by soil resources. On basis of an individual root, oil palm had a lower AMF species richness than forest or rubber tree roots. Our results demonstrate that tropical AMF communities are shaped by two mechanisms: (i) root habitat diversity as the result of plant diversity and (ii) habitat properties as the result of plant traits or environmental conditions and management. Collectively, deterioration of habitat diversity and properties exacerbates impoverishment of AMF assemblages.

The mycorrhiza-specific ammonium transporter ZmAMT3;1 mediates mycorrhiza-dependent nitrogen uptake in maize roots

Most plant species can form symbioses with arbuscular mycorrhizal fungi (AMFs), which may enhance the host plant's acquisition of soil nutrients. In contrast to phosphorus nutrition, the molecular mechanism of mycorrhizal nitrogen (N) uptake remains largely unknown, and its physiological relevance is unclear. Here, we identified a gene encoding an AMF-inducible ammonium transporter, ZmAMT3;1, in maize (Zea mays) roots. ZmAMT3;1 was specifically expressed in arbuscule-containing cortical cells and the encoded protein was localized at the peri-arbuscular membrane. Functional analysis in yeast and Xenopus oocytes indicated that ZmAMT3;1 mediated high-affinity ammonium transport, with the substrate NH4+ being accessed, but likely translocating uncharged NH3. Phosphorylation of ZmAMT3;1 at the C-terminus suppressed transport activity. Using ZmAMT3;1-RNAi transgenic maize lines grown in compartmented pot experiments, we demonstrated that substantial quantities of N were transferred from AMF to plants, and 68%-74% of this capacity was conferred by ZmAMT3;1. Under field conditions, the ZmAMT3;1-dependent mycorrhizal N pathway contributed >30% of postsilking N uptake. Furthermore, AMFs downregulated ZmAMT1;1a and ZmAMT1;3 protein abundance and transport activities expressed in the root epidermis, suggesting a trade-off between mycorrhizal and direct root N-uptake pathways. Taken together, our results provide a comprehensive understanding of mycorrhiza-dependent N uptake in maize and present a promising approach to improve N-acquisition efficiency via plant-microbe interactions.

Recent trends in nitrogen cycle and eco-efficient nitrogen management strategies in aerobic rice system

Rice (Oryza sativa L.) is considered as a staple food for more than half of the global population, and sustaining productivity under a scarcity of resources is challenging to meet the future food demands of the inflating global population. The aerobic rice system can be considered as a transformational replacement for traditional rice, but the widespread adaptation of this innovative approach has been challenged due to higher losses of nitrogen (N) and reduced N-use efficiency (NUE). For normal growth and developmental processes in crop plants, N is required in higher amounts. N is a mineral nutrient and an important constituent of amino acids, nucleic acids, and many photosynthetic metabolites, and hence is essential for normal plant growth and metabolism. Excessive application of N fertilizers improves aerobic rice growth and yield, but compromises economic and environmental sustainability. Irregular and uncontrolled use of N fertilizers have elevated several environmental issues linked to higher N losses in the form of nitrous oxide (N2O), ammonia (NH3), and nitrate (NO3 -), thereby threatening environmental sustainability due to higher warming potential, ozone depletion capacities, and abilities to eutrophicate the water resources. Hence, enhancing NUE in aerobic rice has become an urgent need for the development of a sustainable production system. This article was designed to investigate the major challenge of low NUE and evaluate recent advances in pathways of the N cycle under the aerobic rice system, and thereby suggest the agronomic management approaches to improve NUE. The major objective of this review is about optimizing the application of N inputs while sustaining rice productivity and ensuring environmental safety. This review elaborates that different soil conditions significantly shift the N dynamics via changes in major pathways of the N cycle and comprehensively reviews the facts why N losses are high under the aerobic rice system, which factors hinder in attaining high NUE, and how it can become an eco-efficient production system through agronomic managements. Moreover, it explores the interactive mechanisms of how proper management of N cycle pathways can be accomplished via optimized N fertilizer amendments. Meanwhile, this study suggests several agricultural and agronomic approaches, such as site-specific N management, integrated nutrient management (INM), and incorporation of N fertilizers with enhanced use efficiency that may interactively improve the NUE and thereby plant N uptake in the aerobic rice system. Additionally, resource conservation practices, such as plant residue management, green manuring, improved genetic breeding, and precision farming, are essential to enhance NUE. Deep insights into the recent advances in the pathways of the N cycle under the aerobic rice system necessarily suggest the incorporation of the suggested agronomic adjustments to reduce N losses and enhance NUE while sustaining rice productivity and environmental safety. Future research on N dynamics is encouraged under the aerobic rice system focusing on the interactive evaluation of shifts among activities and diversity in microbial communities, NUE, and plant demands while applying N management measures, which is necessary for its widespread adaptation in face of the projected climate change and scarcity of resources.

Synergism between Streptomyces viridosporus HH1 and Rhizophagus irregularis Effectively Induces Defense Responses to Fusarium Wilt of Pea and Improves Plant Growth and Yield

Fusarium wilt is a detrimental disease of pea crop, resulting in severe damage and a reduction in its yield. Developing synergistically enhanced bioagents for disease management and growth promotion is pivotal for food safety, security, and sustainability. In this study, biocontrol potential of treating pea plants with Streptomycesviridosporus HH1 and/or their colonization with Rhizophagusirregularis against infection with Fusarium wilt was investigated. Impacts on the expression profiles of defense-related genes, biochemical, and ultrastructural levels, as well as the growth and yield of pea plants in response to these treatments, were also investigated. Data obtained indicated the antifungal activity of S. viridosporus HH1 against F. oxysporum f.sp. pisi in vitro. Furthermore, the GC-MS analysis revealed production of different bioactive compounds by S. viridosporus HH1, including 2,3-butanediol, thioglycolic acid, and phthalic acid. The results from the greenhouse experiment exhibited a synergistic biocontrol activity, resulting in a 77% reduction in disease severity in pea plants treated with S. viridosporus HH1 and colonized with R. irregularis. In this regard, this dual treatment overexpressed the responsive factor JERF3 (5.6-fold) and the defense-related genes β-1,3-glucanase (8.2-fold) and the pathogenesis-related protein 1 (14.5-fold), enhanced the total phenolic content (99.5%), induced the antioxidant activity of peroxidase (64.3%) and polyphenol oxidase (31.6%) enzymes in pea plants, reduced the antioxidant stress, and improved their hypersensitivity at the ultrastructural level in response to the Fusarium wilt pathogen. Moreover, a synergistic growth-promoting effect was also recorded in pea plants in response to this dual treatment. In this regard, due to this dual treatment, elevated levels of photosynthetic pigments and improved growth parameters were observed in pea leaves, leading to an increment in the yield (113%). In addition, application of S. viridosporus enhanced the colonization levels with R. irregularis in pea roots. Based on the obtained data, we can conclude that treating pea plants with S. viridosporus HH1 and colonization with R. irregularis have synergistic biocontrol activity and growth-promoting effects on pea plants against Fusarium wilt. Despite its eco-safety and effectiveness, a field evaluation of this treatment before a use recommendation is quite necessary.

Root Reinforcement Improved Performance, Productivity, and Grain Bioactive Quality of Field-Droughted Quinoa (Chenopodium quinoa)

Modern agriculture is facing multiple and complex challenges and has to produce more food and fiber to feed a growing population. Increasingly volatile weather and more extreme events such as droughts can reduce crop productivity. This implies the need for significant increases in production and the adoption of more efficient and sustainable production methods and adaptation to climate change. A new technological and environment-friendly management technique to improve the tolerance of quinoa grown to maturity is proposed using native microbial biostimulants (arbuscular mycorrhizal fungi; AMF) alone, in the consortium, or in combination with compost (Comp) as an organic matter source under two water treatments (normal irrigation and drought stress (DS)). Compared with controls, growth, grain yield, and all physiological traits under DS were significantly decreased while hydrogen peroxide, malondialdehyde, and antioxidative enzymatic functions were significantly increased. Under DS, biofertilizer application reverted physiological activities to normal levels and potentially strengthened quinoa's adaptability to water shortage as compared to untreated plants. The dual combination yielded a 97% improvement in grain dry weight. Moreover, the effectiveness of microbial and compost biostimulants as a biological tool improves grain quality and limits soil degradation under DS. Elemental concentrations, particularly macronutrients, antioxidant potential (1,1-diphenyl-2-picrylhydrazyl radical scavenging activity), and bioactive compounds (phenol and flavonoid content), were accumulated at higher levels in biofertilizer-treated quinoa grain than in untreated controls. The effects of AMF + Comp on post-harvest soil fertility traits were the most positive, with significant increases in total phosphorus (47%) and organic matter (200%) content under drought conditions. Taken together, our data demonstrate that drought stress strongly influences the physiological traits, yield, and quality of quinoa. Microbial and compost biostimulation could be an effective alternative to ensure greater recovery capability, thereby maintaining relatively high levels of grain production. Our study shows that aboveground stress responses in quinoa can be modulated by signals from the microbial/compost-treated root. Further, quinoa grains are generally of higher nutritive quality when amended and inoculated with AMF as compared to non-inoculated and compost-free plants.

Abiotic Stress and Belowground Microbiome: The Potential of Omics Approaches

Nowadays, the worldwide agriculture is experiencing a transition process toward more sustainable production, which requires the reduction of chemical inputs and the preservation of microbiomes’ richness and biodiversity. Plants are no longer considered as standalone entities, and the future of agriculture should be grounded on the study of plant-associated microorganisms and all their potentiality. Moreover, due to the climate change scenario and the resulting rising incidence of abiotic stresses, an innovative and environmentally friendly technique in agroecosystem management is required to support plants in facing hostile environments. Plant-associated microorganisms have shown a great attitude as a promising tool to improve agriculture sustainability and to deal with harsh environments. Several studies were carried out in recent years looking for some beneficial plant-associated microbes and, on the basis of them, it is evident that Actinomycetes and arbuscular mycorrhizal fungi (AMF) have shown a considerable number of positive effects on plants’ fitness and health. Given the potential of these microorganisms and the effects of climate change, this review will be focused on their ability to support the plant during the interaction with abiotic stresses and on multi-omics techniques which can support researchers in unearthing the hidden world of plant–microbiome interactions. These associated microorganisms can increase plants’ endurance of abiotic stresses through several mechanisms, such as growth-promoting traits or priming-mediated stress tolerance. Using a multi-omics approach, it will be possible to deepen these mechanisms and the dynamic of belowground microbiomes, gaining fundamental information to exploit them as staunch allies and innovative weapons against crop abiotic enemies threatening crops in the ongoing global climate change context.

New approaches to improve crop tolerance to biotic and abiotic stresses

During the last years, a great effort has been dedicated at the development and employment of diverse approaches for achieving more stress-tolerant and climate-flexible crops and sustainable yield increases to meet the food and energy demands of the future. The ongoing climate change is in fact leading to more frequent extreme events with a negative impact on food production, such as increased temperatures, drought, and soil salinization as well as invasive arthropod pests and diseases. In this review, diverse "green strategies" (e.g., chemical priming, root-associated microorganisms), and advanced technologies (e.g., genome editing, high-throughput phenotyping) are described on the basis of the most recent research evidence. Particularly, attention has been focused on the potential use in a context of sustainable and climate-smart agriculture (the so called "next agriculture generation") to improve plant tolerance and resilience to abiotic and biotic stresses. In addition, the gap between the results obtained in controlled experiments and those from application of these technologies in real field conditions (lab to field step) is also discussed.

Inoculation with Ericoid Mycorrhizal Associations Alleviates Drought Stress in Lowland and Upland Velvetleaf Blueberry (Vaccinium myrtilloides) Seedlings

Although velvetleaf blueberry (Vaccinium myrtilloides) is usually associated with sandy (upland) areas of the North American boreal forest, lowland populations can be also found in bogs, suggesting possible adaptations to different site conditions. In this study, we examined the role of ericoid mycorrhizal (ERM) fungi in conferring drought resistance to the upland and lowland velvetleaf blueberry seedlings. The seedlings were inoculated with four ERM fungi (Pezicula ericae, Pezoloma ericae, Meliniomyces variabilis, and Oidiodendron maius) isolated from the roots of ericaceous plants and grown under controlled environmental conditions in sterilized soil. The inoculated and non-inoculated (inoculation control) plants were subsequently subjected to three cycles of drought stress by withdrawing watering. Lowland plants appeared to benefit relatively more from mycorrhizal colonization, compared with the upland plants, in terms of plant growth and drought survival. After three weeks of treatments, the dry weights of non-inoculated well-watered upland plants were higher compared to the non-inoculated lowland plants. However, these differences were offset by the inoculation of plants with ERM fungi, some of which also significantly improved drought resistance characteristics of the upland and lowland plants. There were no major differences in the effects of different ERM fungal species on drought responses of upland and lowland plants. Of the examined ericoid mycorrhizal fungi, inoculation with Pezicula ericae was the most effective in conferring drought resistance characteristics to both upland and lowland seedlings and helped maintain higher shoot water potentials, net photosynthetic, and transpiration rates in plants subjected to drought stress.

The Fungal Endophyte Serendipita williamsii Does Not Affect Phosphorus Status but Carbon and Nitrogen Dynamics in Arbuscular Mycorrhizal Tomato Plants

Some members of the root endophytic Serendipitaceae were observed to frequently coexist with arbuscular mycorrhizal fungi (AMF), but their interactions and potential synergistic effects in plants have not yet been well elucidated. Here, we inoculated three-week-old tomato seedlings with Serendipita indica or Serendipita williamsii alone or in combination with the arbuscular mycorrhizal fungus Funneliformis mosseae and cultivated the plants in a greenhouse until the late vegetative stage. Our data show that the simultaneous presence of Serendipita spp. did not affect root colonization by AMF, proving the feasibility of their combination for future agronomic uses. The photosynthetic performance was enhanced in AM tomato plants, although growth remained unresponsive following single or dual inoculation with Serendipita spp. and AMF. With regard to nutrient status under dual inoculation, AMF-induced phosphorus increases remained unaffected, but nitrogen and carbon dynamics were highly altered. Specifically, the application of S. williamsii to mycorrhizal tomato plants significantly enhanced nitrogen concentration in the shoots, but this effect was also compensated with a carbon cost. Our findings indicate that S. williamsii performs differently from S. indica when co-inoculated with AMF, and this suggests an unknown mechanism that needs more detailed investigation.