Mycorrhizal colonisation of cotton in soils differing in sodicity

- Root colonisation by arbuscular mycorrhizal fungi was studied at low to intermediate sodicity.
- Exchangable sodium at less than 10% did not reduce mycorrhizal colonisation of cotton.
- Soil pH and soil P content were associated with colonisation extent at exchangeable sodium <10%.
- P, Zn and Mg uptake was positively correlated with colonisation extent.

Despite the reported importance of mycorrhizal symbioses for early growth and nutrient acquisition of cotton, little is known about how sodicity affects this relationship. Changes in mycorrhizal colonisation and nutrient uptake of cotton in a range of naturally non-sodic (exchangeable sodium percentages (ESP) < 6) and low-sodic soils (ESP 6-10), from cotton production areas in southern Queensland and northern New South Wales, with different ESP (ranged between 1.4 and 9.8) was investigated in a glasshouse experiment. The experiment was a complete factorial design with 11 recently-collected soils and two mycorrhizae treatments (either inoculated with fresh “live” mycorrhizal inoculum or without inoculum). Linear mixed model analysis showed minimal effects of sodicity, when ESP was less than 10, on mycorrhizal colonisation, associated plant growth and nutrient uptake. Principle component and regression analysis showed that other sources of variation including soil pH and soil P content, rather than sodicity, might drive cotton colonisation in Vertosols with low to moderate ESP. The colonisation percentage was positively linearly correlated with P, Mg, and Zn uptake of cotton plants. Further investigation into mycorrhizal spore density and species diversity under sodic soil conditions is warranted.