Arbuscular mycorrhiza: a viable strategy for soil nutrient loss reduction

Wild species rice OsCERK1DY-mediated arbuscular mycorrhiza symbiosis boosts yield and nutrient use efficiency in rice breeding

Meeting the ever-increasing food demands of a growing global population while ensuring resource and environmental sustainability presents significant challenges for agriculture worldwide. Arbuscular mycorrhizal symbiosis (AMS) has emerged as a potential solution by increasing the surface area of a plant's root system and enhancing the absorption of phosphorus, nitrogen nutrients, and water. Consequently, there is a longstanding hypothesis that rice varieties exhibiting more efficient AMS could yield higher outputs at reduced input costs, paving the way for the development of Green Super Rice (GSR). Our prior research study identified a variant, OsCERK1DY, derived from Dongxiang wild-type rice, which notably enhanced AMS efficiency in the rice cultivar "ZZ35." This variant represents a promising gene for enhancing yield and nutrient use efficiency in rice breeding. In this study, we conducted a comparative analysis of biomass, crop growth characteristics, yield attributes, and nutrient absorption at varying soil nitrogen levels in the rice cultivar "ZZ35" and its chromosome single-segment substitution line, "GJDN1." In the field, GJDN1 exhibited a higher AM colonization level in its roots compared with ZZ35. Notably, GJDN1 displayed significantly higher effective panicle numbers and seed-setting rates than ZZ35. Moreover, the yield of GJDN1 with 75% nitrogen was 14.27% greater than the maximum yield achieved using ZZ35. At equivalent nitrogen levels, GJDN1 consistently outperformed ZZ35 in chlorophyll (Chl) content, dry matter accumulation, major nutrient element accumulation, N agronomic efficiency (NAE), N recovery efficiency (NRE), and N partial factor productivity (NPFP). The performance of OsCERK1DY overexpression lines corroborated these findings. These results support a model wherein the heightened level of AMS mediated by OsCERK1DY contributes to increased nitrogen, phosphorus, and potassium accumulation. This enhancement in nutrient utilization promotes higher fertilizer efficiency, dry matter accumulation, and ultimately, rice yield. Consequently, the OsCERK1DY gene emerges as a robust candidate for improving yield, reducing fertilizer usage, and facilitating a transition towards greener, lower-carbon agriculture.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-024-01459-8.

Arbuscular mycorrhizal fungi alleviate erosional soil nitrogen loss by regulating nitrogen cycling genes and enzymes in experimental agro-ecosystems

Nutrient losses from agricultural ecosystems are increasingly threatening global environmental and human health. Although arbuscular mycorrhizal (AM) fungi have the potential to regulate soil nitrogen (N) loss by enhancing plant uptake and soil particle immobilization, the microbial mechanism behind such mycorrhizal effect is unknown. Herein, by conducting a simulated erosion experiment, we compared the effects of exogenous AM fungal inoculation (Funneliformis mosseae) on the gene abundances and enzyme activities of N-cycling processes, and associated such effect to N uptake and loss. The experiment was composed of combinations of two AM fungal treatments (control vs. AM fungal inoculation), two crops (maize vs. soybean) and two slopes of the plots (6° vs. 20°). The experimental plots subjected to natural rainfalls to simulate the erosion events. We showed that the effects of AM fungi were greater in the maize soils than in the soybean soils. In the maize soils, AM fungi increased the abundances of N-fixing (+81.1 %) and nitrifying genes (+200.7 %) and N cycling enzyme activity (+22.3 %). In the soybean soils, AM fungi increased the N-fixing gene abundance (+36.9 %) but decreased the abundance of nitrifying genes (-18.9 %). The abundance of N-fixing gene was positively correlated with N uptake but negatively correlated with N loss. Additionally, AM fungi enhanced the effects of mycorrhizal colonization and moisture but decreased the effects of nutrients on soil microbial metrics related to N-cycling processes. Therefore, AM fungal inoculation enhanced N uptake and reduced N loss by increasing N-fixing gene abundance, and that AM fungi should be preferably used for the low N environments or for the ecosystems highly limited by or competing for N.

Assessing differential land use impacts on soil quality: A method based on log-response ratios and polygonal projections

Soil quality indices (SQI) used for assessing soil degradation are often developed using additive scoring functions. However, these SQI may lack reference values for interpreting their outputs and the capacity to differentiate changes in specific variables. To overcome these limitations, this study introduces SQI using Log Response Ratios (LRR) as measures of size effects caused by land use in physical, chemical, and microbiological soil quality indicators. LRR vectors projected 2D polygons with condensed change measures along their perimeters. This method was tested in andosols within the southeastern region of Antioquia, Colombia. These soils were subjected to contrasting stages of degradation determined by the extent of A-horizon removal due to land use practices. This study shows that mining and agriculture have detrimental effects on soil organic carbon and water contents, and that size effects vary significantly between land uses (p < 0.05). Microbiological features also exhibit distinct size effects, such as populations of culturable mesophilic bacteria and fungi, microbial basal respiration, spore density of arbuscular mycorrhizal fungi (AMF), their diversity, and total glomalin-related soil proteins (p < 0.05). The SQI proposed exhibited a negative correlation with SQI computed from scoring additive functions either considering the entire dataset (R2 = 0.87) or a minimum dataset (R2 = 0.90). This approach underscores the utility of using LRR geometrical analysis to assess global soil quality differences among land uses (p < 0.01), offering a visual, quantifiable representation of the effects of each land use over specific soil quality indicators.

Plant Nutrition-New Methods Based on the Lessons of History: A Review

As with new technologies, plant nutrition has taken a big step forward in the last two decades. The main objective of this review is to briefly summarise the main pathways in modern plant nutrition and attract potential researchers and publishers to this area. First, this review highlights the importance of long-term field experiments, which provide us with valuable information about the effects of different applied strategies. The second part is dedicated to the new analytical technologies (tomography, spectrometry, and chromatography), intensively studied environments (rhizosphere, soil microbial communities, and enzymatic activity), nutrient relationship indexes, and the general importance of proper data evaluation. The third section is dedicated to the strategies of plant nutrition, i.e., (i) plant breeding, (ii) precision farming, (iii) fertiliser placement, (iv) biostimulants, (v) waste materials as a source of nutrients, and (vi) nanotechnologies. Finally, the increasing environmental risks related to plant nutrition, including biotic and abiotic stress, mainly the threat of soil salinity, are mentioned. In the 21st century, fertiliser application trends should be shifted to local application, precise farming, and nanotechnology; amended with ecofriendly organic fertilisers to ensure sustainable agricultural practices; and supported by new, highly effective crop varieties. To optimise agriculture, only the combination of the mentioned modern strategies supported by a proper analysis based on long-term observations seems to be a suitable pathway.

Research progress and prospect of glomalin-related soil protein in the remediation of slightly contaminated soil

Soil pollution caused by organic pollutants and potentially toxic elements poses a serious threat to sustainable agricultural development, global food security and human health. Therefore, strategies for reducing soil pollution are urgently required. Arbuscular mycorrhizal fungi (AMF)-assisted phytoremediation is widely recognized for its ability to remediate slightly-contaminated soil. Glomalin-related soil protein (GRSP) production by AMF is considered a vital mechanism of AMF-assisted phytoremediation. GRSP is widespread in soils and may contribute to the remediation of slightly contaminated soils. GRSP facilitates stabilization of pollutants in soils by interacting with pollutants owing to its abundant functional groups, recalcitrance, and long turnover time. It also enhances soil bioremediation and phytoremediation by stimulating soil microbial activity, improving soil structure, and providing nutrients for plants. However, research on GRSP is still in its early stages, and studies on contaminated soil remediation are limited. The effectiveness of GRSP in situ remediation remains to be proved. This review summarizes current knowledge regarding the GRSP distribution and its contribution to the remediation of slightly contaminated soils. Additionally, we present strategies to increase the GRSP content in contaminated soils, as well as prospects for future studies on the use of GRSP in contaminated soil remediation. This study focuses on recent developments that aim to improve awareness of the role of GRSP in soil remediation and relevant future directions.

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.

Synergistic effects of vegetation and microorganisms on enhancing of biodegradation of landfill gas

The uncontrolled release of landfill gas represents a significant hazard to both human health and ecological well-being. However, the synergistic interactions of vegetation and microorganisms can effectively mitigate this threat by removing pollutants. This study provides a comprehensive review of the current status of controlling landfill gas pollution through the process of revegetation in landfill cover. Our survey has identified several common indicator plants such as Setaria faberi, Sarcandra glabra, and Fraxinus chinensis that grow in covered landfill soil. Local herbaceous plants possess stronger tolerance, making them ideal for the establishment of closed landfills. Moreover, numerous studies have demonstrated that cover plants significantly promote methane oxidation, with an average oxidation capacity twice that of bare soil. Furthermore, we have conducted an analysis of the interrelationships among vegetation, landfill gas, landfill cover soil, and microorganisms, thereby providing a detailed understanding of the potential for vegetation restoration in landfill cover. Additionally, we have summarized studies on the rhizosphere effect and have deduced the mechanisms through which plants biodegrade methane and typical non-methane pollutants. Finally, we have suggested future research directions to better control landfill gas using vegetation and microorganisms.

Arbuscular mycorrhizal fungi influence the uptake of cadmium in industrial hemp (Cannabis sativa L.)

Phytoremediation is currently a more environmentally friendly and economical measure for the remediation of cadmium (Cd) contaminated soil. Heavy metal-resistant plant species, Cannabis sativa L. was inoculated with Rhizophagus irregularis to investigate the mechanisms of mycorrhizal in improving the Cd remediation ability of C. sativa. The results showed that after inoculation with R. irregularis, C. sativa root Cd contents increased significantly, and leaf Cd enrichment decreased significantly. At the transcriptional level, R. irregularis down-regulated the expression of the ABC transporter family but up-regulated differentially expressed genes regulating low molecular weight organic acids. The levels of malic acid, citric acid, and lactic acid were significantly increased in the rhizosphere soil, and they were significantly and strongly related to oxidizable Cd concentrations. Then citric acid levels were considerably and positively connected to exchangeable Cd concentrations. Our findings revealed that through regulating the movement of root molecules, arbuscular mycorrhizal fungus enhanced the heavy metal tolerance of C. sativa even more, meanwhile, they changed the Cd chemical forms by altering the composition of low molecular weight organic acids, which in turn affected soil Cd bioavailability.

The Perspective of Arbuscular Mycorrhizal Symbiosis in Rice Domestication and Breeding

In nature, symbiosis with arbuscular mycorrhizal (AM) fungi contributes to sustainable acquisition of phosphorus and other elements in over 80% of plant species; improving interactions with AM symbionts may mitigate some of the environmental problems associated with fertilizer application in grain crops such as rice. Recent developments of high-throughput genome sequencing projects of thousands of rice cultivars and the discovery of the molecular mechanisms underlying AM symbiosis suggest that interactions with AM fungi might have been an overlooked critical trait in rice domestication and breeding. In this review, we discuss genetic variation in the ability of rice to form AM symbioses and how this might have affected rice domestication. Finally, we discuss potential applications of AM symbiosis in rice breeding for more sustainable agriculture.

Suppression of arbuscular mycorrhizal fungi increased lead uptake in maize leaves and loss via surface runoff and interflow from polluted farmland

Arbuscular mycorrhizal fungi (AMF) are ubiquitous in farmland. But the knowledge on AMF impact on lead (Pb) migration in farmland is limited. A field experiment was conducted in the rainy season (May-October) for two years in a Pb-polluted farmland. Benomyl was used to specifically suppress the native AMF growth in the farmland. The effect of benomyl-induced AMF suppression on the Pb uptake in maize, and Pb loss via surface runoff and interflows (20 cm and 40 cm depth) from the farmland was investigated. The benomyl significantly inhibited the AMF growth, resulting in decreases in the colonization rate, spore number, and contents of total and easily extractable glomalin-related soil protein (GRSP); and promoted the Pb migration into maize shoots and mainly enriched in leaves. The particulate Pb accounted for 83.2%-90.6% of Pb loss via surface runoff, while the proportion of particulate Pb loss via interflow was decreased and the proportion of dissolved Pb loss increased with the increase of soil depth. The AMF suppression led to a decrease in dissolved Pb concentration and loss, but an increase in particulate Pb concentration and loss, and enhanced the total Pb loss via surface runoff and interflows. Moreover, significant or very significant negative correlations were observed between the AMF colonization rate in roots with the Pb uptake in leaves, and the content of easily extractable GRSP with the particulate Pb loss. These results indicated the native AMF contributed to immobilizing Pb in soil and inhibited its migration to crops and the surrounding environment.

Selenium uptake and accumulation in winter wheat as affected by level of phosphate application and arbuscular mycorrhizal fungi

Selenium (Se) is an advantageous element to crops. However, the influence of arbuscular mycorrhizal fungi (AMF), phosphate (P) and selenite in soil on Se uptake by winter wheat remain elusive. Pot trials were carried out including seven levels of P (0, 12.5, 25, 50, 100, 200 or 400 mg kg^-1) and non-mycorrhizal inoculation (NM), inoculation of Funneliformis mosseae (F.m) or Glomus versiforme (G.v). The present results found that grain phosphorus concentration increased with increase of P level from 0 to 100 mg kg^-1 and then tended to plateau, while grain Se concentration decreased with the level of P from 0 to 400 mg kg^-1. Based on mathematical modeling, inoculation of F.m or G.v dramatically improved grain Se concentration by 16.90% or 12.53% under the lower level of P (48.76 mg kg^-1). Furthermore, partial least squares path modeling (PLS-PM) identified that both up-regulated of the expression of AMF-inducible phosphate transporter and improved Se bioavailability in rhizosphere soil contributed to enhancing plant Se concentration under P levels ≤ 100 mg kg^-1. The present study demonstrated that AMF combined with 48.76 mg kg^-1 P applied in soil can not only achieve high grain yield, but also fully exploit the biological potential of Se uptake in wheat.

Arbuscular mycorrhizas increased tomato biomass and nutrition but did not affect local soil P availability or 16S bacterial community in the field

While interest in arbuscular mycorrhizal (AM) fungal effects on soil phosphorus (P) have recently increased, field experiments on this topic are lacking. While microcosm studies provided valuable insights, the lack of field studies represents a knowledge gap. Here, we present a field study in which we grew a mycorrhiza-defective tomato (Solanum lycopersicum L.) genotype (named rmc) and its mycorrhizal wild-type progenitor (named 76R) with and without additional fertiliser, using a drip-irrigation system to examine the impacts of the AM symbiosis on soil P availability and plant growth and nutrition. AM effects on fruit biomass and nutrients, soil nutrient availability, soil moisture and the soil bacterial community were examined. At the time of harvest, the AM tomato plants without fertiliser had the same early season fruit biomass and fruit nutrient concentrations as plants that received fertiliser. The presence of roots reduced the concentration of available soil P, ammonium and soil moisture in the top 10 cm soil layer. Arbuscular mycorrhizas did not significantly affect soil P availability, soil moisture, or 16S bacterial community composition. These findings suggest an indirect role for AM fungi in tomato production but not necessarily a direct role in determining soil physicochemical traits, during the one season that this experiment was conducted. While longer-term field studies may be required in the future, the present study provides new insights into impacts of AM fungi on P availability and uptake in a field soil system.

Arbuscular mycorrhizal fungi mitigate soil nitrogen and phosphorus losses: A meta-analysis

Nutrient loss from terrestrial ecosystems via leaching and gaseous emissions is increasingly threatening global environmental and human health. Although arbuscular mycorrhizal fungi (AMF) have been shown to regulate soil N and P losses, a comprehensive quantitative overview of their influences on the losses of these soil nutrients across global scales is currently lacking. This study used a meta-analysis of 322 observations from 36 studies to assess the effect of AMF inoculum on 11 variables related to the loss of soil N and P. We found that the presence of AMF significantly reduced soil N and P losses, with the most pronounced reduction occurring in soil NO₃^--N (-32%), followed by total P (-21%), available P (-16%) and N₂O (-10%). However, the mitigation effects of AMF on soil N and P loss were dependent on the identity of AMF inoculum, plant type and soil biotic and abiotic factors. Generally, the mitigation effects of AMF increased with increasing AMF root colonization rate, microbial diversity of inoculants, soil organic carbon (SOC) content and experimental duration as well as with decreasing soil sand contents and soil N and P availability. Overall, this meta-analysis highlights the importance of AMF inoculation in mitigating N and P nutrient loss and environmental pollution for terrestrial ecosystem sustainability.

Effect of an arbuscular mycorrhizal fungus on maize growth and cadmium migration in a sand column

The ecological role of arbuscular mycorrhizal fungi (AMF) on altering cadmium (Cd) migration in polluted soil is still unresolved. The present experiment aimed to clarify whether AMF can reduce Cd loss due to leaching at different Cd concentrations (0, 5, 10, and 15 mg L^-1) with maize as a host plant cultured in a sand column. The effects of the arbuscular mycorrhizal fungus Funneliformis mosseae on the root morphology, exudate content, and Cd uptake by maize and Cd loss due to leaching were investigated. The AMF altered the root morphology and exudate content of the maize, resulting in increases in the root length, volume, surface area, tips and branch number and in the contents of soluble sugars, proteins, and amino acids in the root exudates, and the AMF increased maize biomass and Cd uptake by 22.0-31.0%. Moreover, the AMF significantly increased the contents of total and easily extractable glomalin-related soil protein (GRSP), increased Cd adsorption by sand particles and decreased the Cd concentration in the solution at a depth of 20 cm, resulting in a 67.5-97.2% decrease in the Cd loss due to leaching from the sand column. Furthermore, the root exudate content was very significantly positively correlated with Cd adsorption by the sand particles. Root length was significantly positively correlated with Cd uptake by the maize roots, but the average root diameter was very significantly negatively correlated with Cd uptake by maize. Thus, the AMF altered Cd migration by increasing the contents of GRSP and exudates and root morphology, which contributed to reducing the Cd concentration in the solution and Cd loss due to leaching from the sand column. Taken together, these results indicated that AMF serve an ecological function in reducing Cd loss due to leaching from polluted soil.

Seed Priming: A Potential Supplement in Integrated Resource Management Under Fragile Intensive Ecosystems

A majority of agricultural activities are conducted under fragile lands or set-up. The growth and development of crops are negatively affected due to several biotic and abiotic stresses. In the current situation, research efforts have been diverted toward the short-term approaches that can improve crop performance under changing environments. Seed treatment or priming technology is in a transition phase of its popularity among resource-poor farmers. Suitable policy intervention can boost low-cost techniques to implement them on a larger scale in developing countries and to harness the maximum benefits of sustainable food production systems. Primed seeds have high vigor and germination rate that help in seedling growth and successful crop stand establishment under stress conditions. This review is attempted to assess different seed priming techniques in terms of resource use efficiency, crop productivity, cost–benefit balance, and environmental impacts. Moreover, a comprehensive study of the mechanisms (physiological and biochemical) of seed priming is also elaborated. A detailed examination of the applications of priming technology under diverse agroecosystems can improve our understanding of the adaptive management of natural resources.

Mycorrhizal-Bacterial Amelioration of Plant Abiotic and Biotic Stress

Soil microbiota plays an important role in the sustainable production of the different types of agrosystems. Among the members of the plant microbiota, mycorrhizal fungi (MF) and plant growth-promoting bacteria (PGPB) interact in rhizospheric environments leading to additive and/or synergistic effects on plant growth and heath. In this manuscript, the main mechanisms used by MF and PGPB to facilitate plant growth are reviewed, including the improvement of nutrient uptake, and the reduction of ethylene levels or biocontrol of potential pathogens, under both normal and stressful conditions due to abiotic or biotic factors. Finally, it is necessary to expand both research and field use of bioinoculants based on these components and take advantage of their beneficial interactions with plants to alleviate plant stress and improve plant growth and production to satisfy the demand for food for an ever-increasing human population.

Arbuscular mycorrhizal enhancement of phosphorus uptake and yields of maize under high planting density in the black soil region of China

Arbuscular mycorrhizal (AM) symbioses are an attractive means of improving the efficiency of soil phosphorus (P) that difficult to be used by plants and may provide a sustainable way of maintaining high yields while reducing P applications. However, quantifying the contribution of indigenous AM fungi on phosphorus uptake and yields of maize (Zea mays L.) under field conditions is not particularly clear. Mesh-barrier compartments were applied to monitor the distribution of hyphal P uptake throughout the experimental period under different planting densities and soil depths, over two consecutive years. AM symbioses enhanced plant P-acquisition efficiency, especially during the silking stage, and hyphae of AM fungi was assessed to contribution 19.4% at most to total available P content of soil. Moreover, the pattern of AM depletion of soil P generally matched shoot nutrient demand under the high planting density, which resulted in significantly increased yield in 2014. Although the hyphal length density was significantly decreased with soil depth, AM fungi still had high potential for P supply in deeper soil. It demonstrates the great potential of indigenous AM fungi to maize productivity in the high-yield area of China, and it would further provide the possibility of elimination P fertilizer applications to maintain high yields.

An arbuscular mycorrhizal fungus increased the macroaggregate proportion and reduced cadmium leaching from polluted soil

AMF significantly increased the GRSP content and the macroaggregate proportion in soil, which contributed to reducing the Cd concentration in pore water and its leaching loss from soil.

Arbuscular mycorrhizal fungi reduce cadmium leaching from polluted soils under simulated heavy rainfall

Cadmium (Cd)-polluted soils were collected from wasteland, farmland, and slopeland surrounding a lead-zinc mine in Yunnan Province, Southwest China. Maize plants (the host) were inoculated with arbuscular mycorrhizal fungi (AMF) in a dual-compartment cultivation system that included mycorrhizal and hyphal compartments as part of an AMF inoculation treatment and root and soil compartments as part of a the non-inoculation treatment. The effects of AMF on maize biomass and Cd uptake, soil aggregate composition, and Cd concentration in the interflow within two soil layers (0-20 and 20-40 cm) as well as the Cd leaching from these three Cd-polluted soils under simulated heavy rainfall (40 and 80 mm/h) were investigated. The results demonstrated that AMF led to increased maize biomass and Cd uptake. There were greater contents of total glomalin-related soil protein (T-GRSP) and >2.0 mm aggregates and lower Cd concentrations in the interflow and lower dissolved Cd leaching in the mycorrhizal and hyphal compartments than in the soil compartment. A two-way analysis of variance revealed that AMF significantly increased the contents of T-GRSP and >2.0 mm aggregates and reduced both Cd concentrations in the interflow and dissolved Cd leaching. Moreover, AMF interacted extensively with the roots and affected soil aggregate composition and Cd concentrations in the interflow. Under 40 mm/h of rainfall, the contents of T-GRSP and >2.0 mm aggregates were significantly negatively correlated with both Cd concentrations in the interflow and dissolved Cd leaching. In addition, the Cd concentrations in the interflow were significantly positively correlated with the amount of dissolved Cd leaching. Therefore, both AMF-reduced Cd concentrations in the interflow and Cd leaching from Cd-polluted soils were closely related to increased T-GRSP contents and macroaggregate proportion in the soils.

The Interaction of Arbuscular Mycorrhizal Fungi and Phosphorus Inputs on Selenium Uptake by Alfalfa (Medicago sativa L.) and Selenium Fraction Transformation in Soil

Selenium (Se) is a beneficial element to plants and an essential element to humans. Colonization by arbuscular mycorrhizal fungi (AMF) and supply of phosphorus (P) fertilizer may affect the bioavailability of Se in soils and the absorption of Se by plants. To investigate the interaction between AMF and P fertilizer on the transformation of soil Se fractions and the availability of Se in the rhizosphere of alfalfa, we conducted a pot experiment to grow alfalfa in a loessial soil with three P levels (0, 5, and 20 mg kg-1) and two mycorrhizal inoculation treatments (without mycorrhizal inoculation [-AMF] and with mycorrhizal inoculation [+AMF]), and the interaction between the two factors was estimated with two-way ANOVA. The soil in all pots was supplied with Se (Na2SeO3) at 1 mg kg-1. In our results, shoot Se concentration decreased, but plant Se content increased significantly as P level increased and had a significant positive correlation with AMF colonization rate. The amount of total carboxylates in the rhizosphere was strongly affected by AMF. The amounts of rhizosphere carboxylates and alkaline phosphatase activity in the +AMF and 0P treatments were significantly higher than those in other treatments. The concentration of exchangeable-Se in rhizosphere soil had a positive correlation with carboxylates. We speculated that rhizosphere carboxylates promoted the transformation of stable Se (iron oxide-bound Se) into available Se forms, i.e. exchangeable Se and soluble Se. Colonization by AMF and low P availability stimulated alfalfa roots to release more carboxylates and alkaline phosphatase. AMF and P fertilizer affected the transformation of soil Se fractions in the rhizosphere of alfalfa.

Isolation, characterization and inoculation of Cd tolerant rice endophytes and their impacts on rice under Cd contaminated environment

Cadmium (Cd) contamination in paddy soil becomes increasingly prominent in recent years, which endangers the safe production of food crops. Cd-tolerant endophytes are ideal mediators for decreasing Cd content in rice plants, but their effects on the rice endophytic microbial community and gene expression profile have not yet been well elucidated. In this study, 58 endophytic bacteria from rice seeds were isolated and characterized. Five strains of them were selected based on their potential growth-promoting traits and strong Cd tolerance that could grow well under 4 mM Cd²⁺. By 16S ribosomal RNA (rRNA) identification, these five strains were designated as Enterobacter tabaci R2-7, Pantoea agglomerans R3-3, Stenotrophomonas maltophilia R5-5, Sphingomonas sanguinis R7-3 and Enterobacter tabaci R3-2. Pot experiments in relieving Cd stress in rice plants showed that the S. maltophilia R5-5 performed the strongest potential for reducing the Cd content in root and blade by 81.33% and 77.78%, respectively. The endophytic microbial community diversity, richness and composition were significantly altered in S. maltophilia R5-5 inoculated rice plants. Reverse-transcription qPCR (RT-qPCR) showed that the expression of Cd transporters, OsNramp5 and OsHMA2, were down-regulated in S. maltophilia R5-5-innoculated rice roots. The results indicate that the inoculation of endophytic bacteria S. maltophilia R5-5 provides a reference for alleviating the heavy metal contamination in paddy fields and can be a better alternative for guaranteeing the safe production of crops. Changes in the relative abundance of Cd-resistant microorganisms and the expression of Cd transporters might be the intrinsic factors affecting cadmium content in rice.

Natural variation at OsCERK1 regulates arbuscular mycorrhizal symbiosis in rice

The symbiotic interaction between arbuscular mycorrhizal fungi (AMF) and land plants is essential for efficient nutrient acquisition and utilisation. Our understanding of key processes controlling the AMF colonisation in rice is still limited. Dongxiang wild rice (DY) exhibited a stronger colonisation with Rhizophagus irregularis than the rice cultivar Zhongzao 35 (ZZ35). Chromosome segment substitution lines were constructed and the OsCERK1 gene from DY was mapped. Transgenic plants in the japonica rice Zhonghua 11 (ZZ11) were constructed to compare root colonisation by AMF. Chromosome single-segment substitution lines containing OsCERK1^DY showed higher phosphorus content and grain yield relative to ZZ35. Four amino acids substitutions were identified among the OsCERK1 haplotypes of DY, ZZ35 and ZH11 and two of these were in the second lysine-motif domain, which is essential for the differences of AMF colonisation level among rice varieties. Heterologous expression of OsCERK1^DY in ZH11 significantly enhanced AMF colonisation and increased resistance against the pathogenic fungi Magnaporthe oryzae. Notably, the OsCERK1^DY haplotype was absent from 4660 cultivated rice varieties. We conclude that OsCERK1 is a key gene affecting the symbiotic interaction with AMF and OsCERK1^DY has the biotechnological potential to increase rice phosphorus acquisition and utilisation efficiency for sustainable agriculture.