Combined effects of phosphorus and magnesium on mycorrhizal symbiosis through altering metabolism and transport of photosynthates in soybean.

Arbuscular mycorrhizal (AM) symbiosis plays crucial roles in plant nutrient uptake. However, little is known about the combined effects of phosphorus (P) and magnesium (Mg) on mycorrhizal symbiosis. In the present study, a pot experiment was carried out using two soybean genotypes in the presence or absence of Rhizophagus irregularis inoculation under different P and Mg conditions. The results showed that plant growth promotion by mycorrhizal symbiosis was associated with P-starved nutrition status, high Mg supply augmented the efficiency of AM symbiosis in low P, and high Mg relieved the inhibitory effect of high P availability on AM symbiosis. The P-efficient genotype HN89 was more responsive to Mg application than the P-inefficient genotype HN112 when inoculated with Rhizophagus irregularis. The results from a comparative RNA sequencing analysis of the root transcriptomes showed that several carbon metabolism pathways were enriched in mycorrhizal roots in low P plus high Mg. Accordingly, the expression levels of the key genes related to carbon metabolism and transport were also upregulated in mycorrhizal roots. Conversely, the Mg-deficient mycorrhizal plants showed increased sucrose, glucose, and fructose accumulations in shoots. Overall, the results herein demonstrate that P and Mg interactively affect mycorrhizal responses in plants, and high Mg supply has a profound effect on P-starved mycorrhizal plant growth through promotion of photosynthate metabolism and transport in soybean.

Arbuscular mycorrhizal fungi-induced mitigation of heavy metal phytotoxicity in metal contaminated soils: A critical review.

The heavy metal pollution is a worldwide problem and has received a serious concern for the ecosystem and human health. In the last decade, remediation of the agricultural polluted soil has attracted great attention. Phytoremediation is one of the technologies that effectively alleviate heavy metal toxicity, however, this technique is limited to many factors contributing to low plant growth rate and nature of metal toxicities. Arbuscular mycorrhizal fungi (AMF) assisted alleviation of heavy metal phytotoxicity is a cost-effective and environment-friendly strategy. AMF have a symbiotic relationship with the host plant. The bidirectional exchange of resources is a hallmark and also a functional necessity in mycorrhizal symbiosis. During the last few years, a significant progress in both physiological and molecular mechanisms regarding roles of AMF in the alleviation of heavy metals (HMs) toxicities in plants, acquisition of nutrients, and improving plant performance under toxic conditions of HMs has been well studied. This review summarized the current knowledge regarding AMF assisted remediation of heavy metals and some of the strategies used by mycorrhizal fungi to cope with stressful environments. Moreover, this review provides the information of both molecular and physiological responses of mycorrhizal plants as well as AMF to heavy metal stress which could be helpful for exploring new insight into the mechanisms of HMs remediation by utilizing AMF.