Arbuscular mycorrhizal (AM) symbioses are formed by approximately 80% of vascular plant species in all major terrestrial biomes. In consequence an understanding of their functions is critical in any study of sustainable agricultural or natural ecosystems. Here we discuss the implications of recent results and ideas on AM symbioses that are likely to be of particular significance for plants dealing with abiotic stresses such as nutrient deficiency and especially water stress. In order to ensure balanced coverage, we also include brief consideration of the ways in which AM fungi may influence soil structure, carbon deposition in soil and interactions with the soil microbial and animal populations, as well as plantplant competition. These interlinked outcomes of AM symbioses go well beyond effects in increasing nutrient uptake that are commonly discussed and all require to be taken into consideration in future work designed to understand the complex and multifaceted responses of plants to abiotic and biotic stresses in agricultural and natural environments.

Arsenic (As) contamination of soil and water is a global problem that impacts on many areas of biology. This review firstly covers aspects of soil chemistry and soil-plant interactions relevant to the ways plants take up As (particularly arsenate (As(V)) from aerobic soils, with especial attention to As-phosphorus (P) interactions. It then assesses the extent to which studies of plant As tolerance based on short-term uptake of As(V) from nutrient solutions can be extrapolated to longer-term growth in contaminated soil. Mycorrhizal symbioses are then highlighted, because they are formed by~90% of higher plants, often with increased uptake of phosphate (Pi) compared with non-mycorrhizal (NM) counterparts. It is therefore likely that mycorrhizas influence As(V) uptake. Published work shows that arbuscular mycorrhizal (AM) plants (the most common mycorrhizal type) have higher P/As ratios than NM plants, and this would be expected to affect sensitivity to soil As. We discuss ways in which higher P/As selectivity might result from differential operation of P and As uptake pathways in AM compared with NM plants, taking into account new understanding of P uptake mechanisms. We also give suggestions for future research required to increase understanding of mechanisms of As(V) uptake, and its interactions with plant P.

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