Response of alfalfa growth to arbuscular mycorrhizal fungi and phosphate-solubilizing bacteria under different phosphorus application levels

Soil phosphorus transformation and plant uptake driven by phosphate-solubilizing microorganisms

Phosphorus (P) is an important nutrient for plants, and a lack of available P greatly limits plant growth and development. Phosphate-solubilizing microorganisms (PSMs) significantly enhance the ability of plants to absorb and utilize P, which is important for improving plant nutrient turnover and yield. This article summarizes and analyzes how PSMs promote the absorption and utilization of P nutrients by plants from four perspectives: the types and functions of PSMs, phosphate-solubilizing mechanisms, main functional genes, and the impact of complex inoculation of PSMs on plant P acquisition. This article reviews the physiological and molecular mechanisms of phosphorus solubilization and growth promotion by PSMs, with a focus on analyzing the impact of PSMs on soil microbial communities and its interaction with root exudates. In order to better understand the ability of PSMs and their role in soil P transformation and to provide prospects for research on PSMs promoting plant P absorption. PSMs mainly activate insoluble P through the secretion of organic acids, phosphatase production, and mycorrhizal symbiosis, mycorrhizal symbiosis indirectly activates P via carbon exchange. PSMs can secrete organic acids and produce phosphatase, which plays a crucial role in soil P cycling, and related genes are involved in regulating the P-solubilization ability. This article reviews the mechanisms by which microorganisms promote plant uptake of soil P, which is of great significance for a deeper understanding of PSM-mediated soil P cycling, plant P uptake and utilization, and for improving the efficiency of P utilization in agriculture.

Isolation and Identification of Acer truncatum Endophytic Fungus Talaromyces verruculosus and Evaluation of Its Effects on Insoluble Phosphorus Absorption Capacity and Growth of Cucumber Seedlings

The symbiosis between endophytic fungi and plants can promote the absorption of potassium, nitrogen, phosphorus, and other nutrients by plants. Phosphorus is one of the indispensable nutrient elements for plant growth and development. However, the content of available phosphorus in soil is very low, which limits the growth of plants. Phosphorus-soluble microorganisms can improve the utilization rate of insoluble phosphorus. In this study, Talaromyces verruculosus (T. verruculosus), a potential phosphorus-soluble fungus, was isolated from Acer truncatum, a plant with strong stress resistance, and its phosphorus-soluble ability in relation to cucumber seedlings under different treatment conditions was determined. In addition, the morphological, physiological, and biochemical indexes of the cucumber seedlings were assessed. The results show that T. verruculosus could solubilize tricalcium phosphate (TCP) and lecithin, and the solubilization effect of lecithin was higher than that of TCP. After the application of T. verruclosus, the leaf photosynthetic index increased significantly. The photosynthetic system damage caused by low phosphorus stress was alleviated, and the root morphological indexes of cucumber seedlings were increased. The plant height, stem diameter, and leaf area of cucumber seedlings treated with T. verruculosus were also significantly higher than those without treatment. Therefore, it was shown that T. verruculosus is a beneficial endophytic fungus that can promote plant growth and improve plant stress resistance. This study will provide a useful reference for further research on endophytic fungi to promote growth and improve plant stress resistance.

Phosphate-Solubilizing Bacteria: Advances in Their Physiology, Molecular Mechanisms and Microbial Community Effects

Phosphorus is an essential nutrient for all life on earth and has a major impact on plant growth and crop yield. The forms of phosphorus that can be directly absorbed and utilized by plants are mainly HPO42- and H2PO4-, which are known as usable phosphorus. At present, the total phosphorus content of soils worldwide is 400-1000 mg/kg, of which only 1.00-2.50% is plant-available, which seriously affects the growth of plants and the development of agriculture, resulting in a high level of total phosphorus in soils and a scarcity of available phosphorus. Traditional methods of applying phosphorus fertilizer cannot address phosphorus deficiency problems; they harm the environment and the ore material is a nonrenewable natural resource. Therefore, it is imperative to find alternative environmentally compatible and economically viable strategies to address phosphorus scarcity. Phosphorus-solubilizing bacteria (PSB) can convert insoluble phosphorus in the soil into usable phosphorus that can be directly absorbed by plants, thus improving the uptake and utilization of phosphorus by plants. However, there is no clear and systematic report on the mechanism of action of PSB. Therefore, this paper summarizes the discovery process, species, and distribution of PSB, focusing on the physiological mechanisms outlining the processes of acidolysis, enzymolysis, chelation and complexation reactions of PSB. The related genes regulating PSB acidolysis and enzymatic action as well as genes related to phosphate transport and the molecular direction mechanism of its pathway are examined. The effects of PSB on the structure and abundance of microbial communities in soil are also described, illustrating the mechanism of how PSB interact with microorganisms in soil and indirectly increase the amount of available phosphorus in soil. And three perspectives are considered in further exploring the PSB mechanism in utilizing a synergistic multi-omics approach, exploring PSB-related regulatory genes in different phosphorus levels and investigating the application of PSB as a microbial fungicide. This paper aims to provide theoretical support for improving the utilization of soil insoluble phosphorus and providing optimal management of elemental phosphorus in the future.

Effect the accumulation of bioactive constituents of a medicinal plant (Salvia Miltiorrhiza Bge.) by arbuscular mycorrhizal fungi community

BACKGROUND

Arbuscular mycorrhizal fungi (AMF) form symbiotic relationships with various terrestrial plants and have attracted considerable interest as biofertilizers for improving the quality and yield of medicinal plants. Despite the widespread distribution of AMFs in Salvia miltiorrhiza Bunge's roots, research on the impact of multiple AMFs on biomass and active ingredient accumulations has not been conducted. In this study, the effects of five native AMFs (Glomus formosanum, Septoglomus constrictum, Rhizophagus manihotis, Acaulospora laevis, and Ambispora gerdemannii) and twenty-six communities on the root biomass and active ingredient concentrations of S. miltiorrhiza were assessed using the total factor design method.

RESULTS

Thirty-one treatment groups formed symbiotic relationships with S. miltiorrhiza based on the pot culture results, and the colonization rate ranged from 54.83% to 89.97%. AMF communities had higher colonization rates and total phenolic acid concentration than single AMF, and communities also appeared to have higher root fresh weight, dry weight, and total phenolic acid concentration than single inoculations. As AMF richness increased, there was a rising trend in root biomass and total tanshinone accumulations (ATTS), while total phenolic acid accumulations (ATP) showed a decreasing trend. This suggests that plant productivity was influenced by the AMF richness, with higher inoculation benefits observed when the communities contained three or four AMFs. Additionally, the affinities of AMF members were also connected to plant productivity. The inoculation effect of closely related AMFs within the same family, such as G. formosanum, S. constrictum, and R. manihotis, consistently yielded lower than that of mono-inoculation when any combinations were applied. The co-inoculation of S. miltiorrhiza with nearby or distant AMFs from two families, such as G. formosanum, R. manihotis, and Ac. laevis or Am. gerdemannii resulted in an increase of ATP and ATTS by more than 50%. AMF communities appear to be more beneficial to the yield of bioactive constituents than the single AMF, but overall community inoculation effects are related to the composition of AMFs and the relationship between members.

CONCLUSION

This study reveals that the AMF community has great potential to improve the productivity and the accumulation of bioactive constituents in S. miltiorrhiza, indicating that it is an effective way to achieve sustainable agricultural development through using the AMF community.

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.

Effects of Interaction between Claroideogolmus etuicatum and Bacillus aryabhattai on the Utilization of Organic Phosphorus in Camellia oleifera Abel

Arbuscular mycorrhizal fungi (AMF) and phosphate solubilizing bacteria (PSB) are involved in phosphorus (P) mobilization and turnover; however, the impact of their interaction on plant P absorption and organic P mineralization in the hyphosphere (rootless soil) are unknown. This study examined the interactive effects of two native microorganisms, namely Claroideogolmus etuicatum and Bacillus aryabhattai, and the effects of co-inoculation of both microorganisms on organic P mineralization and the subsequent transfer to Camellia oleifera, using a three-compartment microcosm with a nylon mesh barrier. The results demonstrated that the co-inoculation treatment (AMF + PSB) significantly increased the plant P content and biomass accumulation in C. oleifera compared to those of the non-inoculated control. Furthermore, co-inoculation boosted soil phosphatase and phytase activities as well as the liable P content. Compared to the non-inoculated control, inoculation of AMF decreased the NaOH-Po content. A correlation analysis showed that AMF colonization and hyphal density was significantly positively correlated with H2O-P and NaHCO3-Pi and negatively correlated with NaOH-Po. It was shown that co-inoculation could increase phosphatase activity, phytase activity, and promote the liable P content, thus increasing the phosphorus content and biomass accumulation of C. oleifera. In conclusion, AMF and PSB interactively enhanced the mineralization of soil organic P, and therefore positively affected P uptake and plant growth.

Effect of Trichoderma viride on insoluble phosphorus absorption ability and growth of Melilotus officinalis

Phosphorus (Pi) deficiency is a major factor of limiting plant growth. Using Phosphate-solubilizing microorganism (PSM) in synergy with plant root system which supply soluble Pi to plants is an environmentally friendly and efficient way to utilize Pi. Trichoderma viride (T. viride) is a biocontrol agent which able to solubilize soil nutrients, but little is known about its Pi solubilizing properties. The study used T. viride to inoculate Melilotus officinalis (M. officinalis) under different Pi levels and in order to investigate the effect on Pi absorption and growth of seedlings. The results found that T. viride could not only solubilizate insoluble inorganic Pi but also mineralize insoluble organic Pi. In addition, the ability of mineralization to insoluble organic Pi is more stronger. Under different Pi levels, inoculation of T. viride showed that promoted the growth of aboveground parts of seedlings and regulated the morphology of roots, thus increasing the dry weight of seedlings. The effect of T. viride on seedling growth was also reflected the increasing of chlorophyll fluorescence parameters and photosynthetic pigment content. Moreover, compared to the uninoculated treatments, inoculation of T. viride also enhanced Pi content in seedlings. Thus, the T. viride was a beneficial fungus for synergistic the plant Pi uptake and growth.

Nutrient availability of roughages in isocaloric and isonitrogenous diets alters the bacterial networks in the whole gastrointestinal tract of Hu sheep

BACKGROUND

The nutrient availability of roughages could affect the dietary utilization efficiency of ruminants even in isocaloric and isonitrogenous diets. Here, we analyzed the bacterial composition and their metabolic pathways in the gastrointestinal tracts (GITs) of Hu sheep fed with wheat straw (WS) instead of alfalfa (AL) in isocaloric and isonitrogenous diets, trying to explore the reasons from the perspective of GITs bacterial network structure changes.

RESULTS

We employed 16S rRNA gene sequencing in combination with the Kruskal-Wallis test, Spearman correlation analysis, and other statistical methods to describe the microbiota composition in the GITs of Hu sheep. The results showed after the roughage was replaced from AL to WS, the most positive response occurred in the rumen microbiota, resulting in a more obvious microbiological and functional redundancy phenomenon. Whereas extended biogeographic studies of the GITs bacterial community found opposite results for the hindgut microbiota and metabolism networks compared to the forestomach. The abundance of fiber-degrading bacteria such as Prevotella, Oscillospiraceae NK4A214 group, and Treponema was significantly increased in GITs, but low-efficiency crude fiber degradation inhibited energy use efficiency, the pentose phosphate pathway, gluconeogenesis, and volatile acid synthesis. In addition, dietary shifting from AL to WS decreased the abundance of beneficial bacteria such as the Lachnospiraceae NK3A20 group and Alistipes, thereby enhancing the underlying inflammatory response.

CONCLUSIONS

These findings suggest that feeding untreated WS affected the structure and function of the bacterial network in the GITs due to limited total digestible nutrients, and in particular increases the complexity of the rumen bacterial network, and limit the abundance of bacteria involved in the crude fiber degradation in the hindgut.

Yield and quality of alfalfa (Medicago sativa L.) in response to fertilizer application in China: A meta-analysis

INTRODUCTION

In China, alfalfa (Medicago sativa L.) often grows in marginal land with poor soil fertility and suboptimal climate conditions. Alfalfa production cannot meet demands both in yield and quality. It is necessary to apply fertilizers to achieve high yields and produce high-quality alfalfa in China. However, there is no understanding on the impact of fertilizer application on alfalfa production and the possible optimal application rates across China.

METHODS

We conducted a meta-analysis to explore the contribution of fertilizer application to the yield and quality of alfalfa based on a dataset from 86 studies published between 2004 and 2022.

RESULTS AND DISCUSSION

The results showed that fertilizer application not only increased alfalfa yield by 19.2% but also improved alfalfa quality by increasing crude protein (CP) by 7.7% and decreasing acid detergent fibre by 2.9% and neutral detergent fibre by 1.8% overall compared to the non-fertilizer control levels. The combined nitrogen (N), phosphorus (P) and potassium (K) and combined NP fertilizer applications achieved the greatest yield and CP concentration increases of 27.0% and 13.5%, respectively. Considering both yield and quality, the optimal rate of fertilizer application ranged from 30 to 60 kg ha^-1 for N, 120 to 150 kg ha^-1 for P and less than 120 kg ha^-1 for K. Meta-analysis further showed that the effect of fertilizer application on yield was greater in low soil organic matter (SOM) soils than in high SOM soils. In conclusion, fertilizer application is an effective strategy to improve the yield and quality of alfalfa in China, especially that grown in low SOM soils. This study is helpful for optimizing fertilization schedules of alfalfa in China.

Enhanced legume growth and adaptation to degraded estuarine soils using Pseudomonas sp. nodule endophytes

The joint estuary of Tinto and Odiel rivers (SW Spain) is one of the most degraded and polluted areas in the world and its recovery is mandatory. Legumes and their associated bacteria are recommended sustainable tools to fight against soils degradation and loss of fertility due to their known positive impacts on soils. The aim of this work was to isolate and characterize plant growth promoting nodule endophytes (PGPNE) from inside nodules of Medicago spp. naturally growing in the estuary of the Tinto and Odiel Rivers and evaluate their ability to promote legume adaptation in degraded soils. The best rhizobia and non-rhizobia among 33 endophytes were selected based on their plant growth promoting properties and bacterial enzymatic activities. These strains, identified as Pseudomonas sp. N4, Pseudomonas sp. N8, Ensifer sp. N10 and Ensifer sp. N12, were used for in vitro studies using Medicago sativa plants. The effects of individual or combined inoculation on seed germination, plant growth and nodulation were studied, both on plates and pots containing nutrient-poor soils and moderately contaminated with metals/loids from the estuary. In general, inoculation with combinations of rhizobia and Pseudomonas increased plant biomass (up to 1.5-fold) and nodules number (up to 2-fold) compared to single inoculation with rhizobia, ameliorating the physiological state of the plants and helping to regulate plant stress mechanisms. The greatest benefits were observed in plants inoculated with the consortium containing the four strains. In addition, combined inoculation with Ensifer and Pseudomonas increased As and metals accumulation in plant roots, without significant differences in shoot metal accumulation. These results suggest that PGPNE are useful biotools to promote legume growth and phytostabilization potential in nutrient-poor and/or metals contaminated estuarine soils.

Arbuscular mycorrhizal Fungi and Changes in Primary and Secondary Metabolites

Medicinal and aromatic plants (MAPs) are able to synthesize a diverse group of secondary metabolites (SMs) such as terpenoids or terpenes, steroids, phenolics, and alkaloids with a broad range of therapeutic and pharmacological potentials. Extensive use of MAPs in various industries makes it important to re-evaluate their research, development, production, and use. In intensive agricultural systems, increasing plant productivity is highly dependent on the application of chemical inputs. Extreme use of chemical or synthetic fertilizers, especially higher doses of N fertilization, decrease the yield of bioactive compounds in MAPs. The plant-soil microbial interaction is an eco-friendly strategy to decrease the demand of chemical fertilizers. Arbuscular mycorrhizal fungi (AMF), belongs to phylum Glomeromycota, can form mutualistic symbiotic associations with more than 80% of plant species. The AMF-plant symbiotic association, in addition to increasing nutrient and water uptake, reprograms the metabolic pathways of plants and changes the concentration of primary and secondary metabolites of medicinal and aromatic plants. The major findings reported that inoculation of AMF with MAPs enhanced secondary metabolites directly by increasing nutrient and water uptake and also improving photosynthesis capacity or indirectly by stimulating SMs' biosynthetic pathways through changes in phytohormonal concentrations and production of signaling molecules. Overall, the AMF-MAPs symbiotic association can be used as new eco-friendly technologies in sustainable agricultural systems for improving the quantity and quality of MAPs.

Role of Nodulation-Enhancing Rhizobacteria in the Promotion of Medicago sativa Development in Nutrient-Poor Soils

Legumes are usually used as cover crops to improve soil quality due to the biological nitrogen fixation that occurs due to the interaction of legumes and rhizobia. This symbiosis can be used to recover degraded soils using legumes as pioneer plants. In this work, we screened for bacteria that improve the legume–rhizobia interaction in nutrient-poor soils. Fourteen phosphate solubilizer-strains were isolated, showing at least three out of the five tested plant growth promoting properties. Furthermore, cellulase, protease, pectinase, and chitinase activities were detected in three of the isolated strains. Pseudomonas sp. L1, Chryseobacterium soli L2, and Priestia megaterium L3 were selected to inoculate seeds and plants of Medicago sativa using a nutrient-poor soil as substrate under greenhouse conditions. The effects of the three bacteria individually and in consortium showed more vigorous plants with increased numbers of nodules and a higher nitrogen content than non-inoculated plants. Moreover, bacterial inoculation increased plants’ antioxidant activities and improved their development in nutrient-poor soils, suggesting an important role in the stress mechanisms of plants. In conclusion, the selected strains are nodulation-enhancing rhizobacteria that improve leguminous plants growth and nodulation in nutrient-poor soils and could be used by sustainable agriculture to promote plants’ development in degraded soils.

Effects of agrochemicals on the beneficial plant rhizobacteria in agricultural systems

Conventional agriculture relies heavily on chemical pesticides and fertilizers to control plant pests and diseases and improve production. Nevertheless, the intensive and prolonged use of agrochemicals may have undesirable consequences on the structure, diversity, and activities of soil microbiomes, including the beneficial plant rhizobacteria in agricultural systems. Although literature continues to mount regarding the effects of these chemicals on the beneficial plant rhizobacteria in agricultural systems, our understanding of them is still limited, and a proper account is required. With the renewed efforts and focus on agricultural and environmental sustainability, understanding the effects of different agrochemicals on the beneficial plant rhizobacteria in agricultural systems is both urgent and important to deduce practical solutions towards agricultural sustainability. This review critically evaluates the effects of various agrochemicals on the structure, diversity, and functions of the beneficial plant rhizobacteria in agricultural systems and propounds on the prospects and general solutions that can be considered to realize sustainable agricultural systems. This can be useful in understanding the anthropogenic effects of common and constantly applied agrochemicals on symbiotic systems in agricultural soils and shed light on the need for more environmentally friendly and sustainable agricultural practices.

Phosphorus Nutrition and Growth of Cotton Plants Inoculated With Growth-Promoting Bacteria Under Low Phosphate Availability

The low availability of phosphorus (P) in the soil drastically limits the world productivity of crops such as cotton. In order to contribute sustainably to the solution of this problem, the current study aimed to evaluate the capacity of phosphate-solubilising bacteria to improve plant growth and its relationship with physiological parameters, as well as the shoot P content in cotton plants in a soil with low P availability amended with rock phosphate. The results showed that, of the six plant growth-promoting bacteria strains evaluated under greenhouse conditions, the Rhizobium strain B02 significantly promoted growth, shoot P content and photosynthetic rate. This strain also improved the transpiration rate and the relative content of chlorophyll but without significant differences. Remarkably, Rhizobium sp. B02 had a more significant effect on plant growth compared to the P nutrition. Furthermore, the effect of its inoculation was more pronounced on the roots' growth compared to the shoot. Finally, application of Rhizobium strain B02 showed the capacity to optimize the use of low-solubility fertilizer as the rock phosphate. These findings could be associated with the metabolic activities of plant growth promotion exhibited by phosphate-solubilising strains, such as phosphate solubilisation, production of indole compounds and siderophores synthesis. In conclusion, this research provides evidence of the biotechnological potential of the Rhizobium genus as phosphate-solubilising bacteria with multiple plant growth-promoting activities capable of improving the plant growth and phosphate nutrition of non-leguminous crops such as cotton in soil with low P availability amended with rock phosphate.

Effect of plant growth promotion fungi on agricultural crops

Pot experiments with seven agricultural crops were carried out in laboratory conditions to study the effect of fungal strains on their growth and development: soybean (Glycine max), barley (Hordeum vulgare), alfalfa (Medicago sativa), rapeseed (Brassica napus), safflower (Carthamus tinctorius), sweet clover (Melilotus officinalis), sainfoin (Onobrychis viciifolia). Five fungal strains with biotechnologically valuable properties were used: P. bilaiae Pb14, P. bilaiae C11, T. pinophilus T14, Aspergillus sp. D1 and B. bassiana T7. Inoculation with fungal strains increased theshoot length of seedlings by 14-33%, the root length by 13-29%, the shoot dry weight by 12-31%, the root dry weight by 15-30% compared to the controls.The application of fungal strains had a stimulating effect on the photosynthetic activity of plants by increasing the content of chlorophyll in the leaves of seedlings. There was an increase in the content of chlorophyll a by 8-16%, chlorophyll b - by 9-17%.