Mycorrhizal contribution to phosphorus nutrition of cotton in low and highly sodic soils using dual isotope labelling (32P and 33P)

Abstract

Little is known about how the adverse physical and chemical environment in sodic soils affects plant-mycorrhizal relationships. We investigated mycorrhizal colonisation and plant nutrient uptake of cotton plants under highly stressed (Exchangeable Na percentage (ESP) 21) and less stressed (ESP 7) conditions with two rates of applied P. The relative hyphal contribution to P uptake was quantified using dual isotope labelling techniques (32P and 33P). Root colonisation and P uptake of mycorrhizal cotton plants reduced by 16% and 20%, respectively, in highly sodic soil as compared to plants in low sodic soil, however, the relative proportion of P delivered via hyphal pathways (32P from root-free hyphal compartment) was similar. Under high P conditions, the relative increase in the proportion of 33P (root + hyphae compartment) taken up by inoculated plants was greater in the low sodic soil relative to the high sodic soil. Mycorrhization improved early seedling vigour, and nutrient uptake. Reduced colonisation and hyphal exploration of the soil, possibly due to the physical and chemical constraints imposed by highly-sodic soil, rather than poorer mycorrhizal function, may be responsible for limited early P uptake of cotton in highly-sodic soil.