Mycorrhizal colonization status of lowland rice (Oryza sativa L.) in the southeastern region of China

Ecology and diversity of arbuscular mycorrhizal fungi (AMF) in rice (Oryza sativa L.) in South India: an ecological analysis of factors influencing AMF in rice fields

AIMS

This study examined the diversity of arbuscular mycorrhizal fungi (AMF), mean spore density (MSD), and root colonization in relation to factors such as agroclimatic zones, rice varieties and soil types in paddy fields of South India. The aim was to understand how these factors influence AMF association in rice, facilitating their effective use as a biological tool in paddy cultivation.

METHODS AND RESULTS

AMF were identified through light microscopy of spores, while MSD and percentage-root-length colonization (PRLC) were measured using standard methods. Correlation and principal component analyses were performed to explore the interrelationships between AMF characteristics and various environmental, soil, and plant variables. Sixteen AMF species were identified across 29 rice varieties from three agroclimatic zones, 6 soil orders, and 18 soil series over 2 seasons. Notably, 70% of chemicalized rice fields lacked AMF spores, and only 50% exhibited root colonization. This study offers new insights into the role of AMF in rice cultivation.

CONCLUSION

The AMF diversity and root colonization in relation to environmental variables underscore their significant impact on AMF in particular crop fields.

Effects of Antimony on Rice Growth and Its Existing Forms in Rice Under Arbuscular Mycorrhizal Fungi Environment

Arbuscular mycorrhizal fungi (AMF) can form symbiotic relationships with most terrestrial plants and regulate the uptake and distribution of antimony (Sb) in rice. The effect of AMF on the uptake and transport of Sb in rice was observed using pot experiments in the greenhouse. The results showed that AMF inoculation increased the contact area between roots and metals by forming mycelium, and changed the pH and Eh of the root soil, leading to more Sb entering various parts of the rice, especially at an Sb concentration of 1,200 mg/kg. The increase in metal toxicity further led to a decrease in the rice chlorophyll content, which directly resulted in a 22.7% decrease in aboveground biomass, 21.7% in underground biomass, and 11.3% in grain biomass. In addition, the antioxidant enzyme results showed that inoculation of AMF decreased 22.3% in superoxide dismutase, 9.9% in catalase, and 20.7% in peroxidase compared to the non-inoculation groups, further verifying the negative synergistic effect of AMF inoculation on the uptake of Sb in rice. The present study demonstrated the effect of AMF on the uptake and transport of Sb in the soil–rice system, facilitating future research on the related mechanism in the soil–rice system under Sb stress.

Potential use of arbuscular mycorrhizal fungi for simultaneous mitigation of arsenic and cadmium accumulation in rice

Rice polluted by metal(loid)s, especially arsenic (As) and cadmium (Cd), imposes serious health risks. Numerous studies have demonstrated that the obligate plant symbionts arbuscular mycorrhizal fungi (AMF) can reduce As and Cd concentrations in rice. The behaviours of metal(loid)s in the soil-rice-AMF system are of significant interest for scientists in the fields of plant biology, microbiology, agriculture, and environmental science. We review the mechanisms of As and Cd accumulation in rice with and without the involvement of AMF. In the context of the soil-rice-AMF system, we assess and discuss the role of AMF in affecting soil ion mobility, chemical forms, transport pathways (including the symplast and apoplast), and genotype variation. A potential strategy for AMF application in rice fields is considered, followed by future research directions to improve theoretical understanding and encourage field application.

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

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

Symbiosis of isoetid plant species with arbuscular mycorrhizal fungi under aquatic versus terrestrial conditions

Arbuscular mycorrhizal fungi (AMF) colonize the roots of numerous aquatic and wetland plants, but the establishment and functioning of mycorrhizal symbiosis in submerged habitats have received only little attention. Three pot experiments were conducted to study the interaction of isoetid plants with native AMF. In the first experiment, arbuscular mycorrhizal (AM) symbiosis did not establish in roots of Isoëtes echinospora and I. lacustris, while Littorella uniflora roots were highly colonized. Shoot and root biomass of L. uniflora were, however, not affected by AMF inoculation, and only one of nine AMF isolates significantly increased shoot P concentration. In the second experiment, we compared colonization by three Glomus tetrastratosum isolates of different cultivation history and origin (aquatic versus terrestrial) and their effects on L. uniflora growth and phosphorus nutrition under submerged versus terrestrial conditions. The submerged cultivation considerably slowed, but did not inhibit mycorrhizal root colonization, regardless of isolate identity. Inoculation with any AMF isolate improved plant growth and P uptake under terrestrial, but not submerged conditions. In the final experiment, we compared the communities of AMF established in two cultivation regimes of trap cultures with lake sediments, either submerged on L. uniflora or terrestrial on Zea mays. After 2-year cultivation, we did not detect a significant effect of cultivation regime on AMF community composition. In summary, although submerged conditions do not preclude the development of functional AM symbiosis, the contribution of these symbiotic fungi to the fitness of their hosts seems to be considerably less than under terrestrial conditions.

Variation in arbuscular mycorrhizal fungal communities associated with lowland rice (Oryza sativa) along a gradient of soil salinity and arsenic contamination in Bangladesh

Rice is an essential food crop that nourishes >50% of the world population. In many regions of Bangladesh rice production is constrained by high soil salinity and heavy metal contamination due to irrigation practices. Plants may naturally overcome such stress through mutualistic interactions with arbuscular mycorrhizal fungi (AMF). Yet, little is known regarding the diversity and composition of AMF communities in rice fields with high saline and arsenic concentration. Here we used high throughput Illumina sequencing to characterize AMF communities in rice roots from 45 Bangladeshi rice fields, along a large geographical gradient of soil salinity and arsenic contamination. We obtained 77 operational taxonomic units (OTUs, based on a sequence similarity threshold of 97%) from eight AMF families, and showed that high soil salinity and arsenic concentration are significantly associated with low AMF diversity in rice roots. Soil salinity and arsenic concentration also explained a large part of the variation in AMF community composition, but also soil pH, moisture, organic matter content and plant available soil phosphorus played an important role. Overall, our study showed that even at very high salinity and arsenic levels, some AMF OTUs are present in rice roots. Their potential role in mediating a reduction of rice stress and arsenic uptake remains to be investigated.