Flooding overshadows phosphorus availability in controlling the intensity of arbuscular mycorrhizal colonization in Sangyod Muang Phatthalung lowland indica rice

Abstract

Phosphorus (P) availability and soil water are two important environmental factors in lowland rice paddies. They limit the ability of rice to form mutualistic associations with arbuscular mycorrhizal fungi (AMF). The dynamics of this symbiotic interaction are intensified by phosphorus deficiency and attenuated by anaerobic conditions. However, the effects of combined phosphorus deficiency and anaerobic conditions on AMF symbiosis in paddy soil were unproven. The main objective of this study is to determine the influence of phosphorus and water availabilities on indigenous AMF colonization and community in Sangyod Muang Phatthalung (SMP) rice. Rice seedlings were grown in pots containing P-deficient organic paddy soil with or without phosphorus fertilization under non-flooded and flooded conditions for 2, 4 and 6 weeks. The application and omission of P soil fertilization influenced phosphate accumulations in rice seedlings, producing conditions of P-sufficiency and P-deficiency, respectively, in the plants. To determine the effects of phosphorus and water availabilities on AMF colonization and community structures, roots were analyzed microscopically and molecularly. Flooding considerably reduced the intensity of indigenous AMF root colonization whereas the nonenrichment of P availability did not. Reduced AMF colonization was concomitant with lower abundances of two major Glomeromycota ASVs in roots under flooding. This result suggested that soil water availability plays the primary role in shaping AMF communities in SMP roots. This study emphasized the primacy of water management when considering the use of AMF in the production of SMP rice in an organic cultivation system.

Acaulospora as the Dominant Arbuscular Mycorrhizal Fungi in Organic Lowland Rice Paddies Improves Phosphorus Availability in Soils

“…Our previous study showed that flooding plays a major role in shaping fungal communities and significantly reduced AMF colonization and AMF abundance in the roots of the SMP landrace rice variety grown in organic rice paddy soil. Only eight amplicon sequence variants of the fungal ITS sequences belonged Glomeraceae, which seems to underestimate the total AMF species in the study site [5]. Moreover, the molecular identification of AMF at the genus or species level by the ITS region is limited.…”

“…Genomic DNA samples of roots of Sangyod Muang Phatthalung (SMP) rice plants grown in non-flooded and flooded conditions for 6 weeks were obtained from our previous study [5]. To identify the 1.5-kb SSU-ITS-LSU sequences of AMF present in the roots, nested PCR was run with Kruger primers [21].…”

“…In a pot 20 cm in height and 24 cm in diameter, the same batch of organic paddy soil used in our previous study [5] was mixed 1:3 (v/v) with sterile sand to be used for a trap culture using maize as the host plant. Acaulospora spores were isolated by the wet sieving and decanting method [27] and used to obtain a monospore culture.…”

“…The flooded condition induces the formation of aerenchyma in the root cortex, reducing the accommodation of AMF and the degree of AMF symbiosis in rice roots [4]. Moreover, flooding displays a stronger impact on the intensity of AMF colonization than soil P availability [2,5].…”

Microbial Contributions for Rice Production: From Conventional Crop Management to the Use of ‘Omics’ Technologies

“…For example, Klinnawee et al [ 42 ] have documented that under water-saturated soil conditions, the symbiotic relationship between mycorrhizal fungi and lowland (flooded) rice plant roots is diminished because, as aerobic microbes, these organisms similar to other fungi are greatly affected by the amount of water in the soil, which determines the availability of oxygen. ITS2 sequencing analysis has shown that keeping rice paddies inundated inhibits the extent of fungal communities in the soil and reduces the abundance of mycorrhizal fungi in rice roots [ 42 ].…”