Colonisation with the arbuscular mycorrhizal fungus Glomus mosseae (Nicol. & Gerd.) enhanced phosphorus uptake from dry soil in Sorghum bicolor (L.)

The aim of the present study was to quantify the contribution of AMF to phosphorus (P) nutrition of the host plant when the P availability in the soil was limited by drought. To investigate the potential of AMF hyphae in taking up P from dry soil, mycorrhizal [+M] and nonmycorrhizal [-M]Sorghum bicolor L. plants were grown in a vertical split root system that consisted of two compartments placed upon one the other. The upper compartment was filled with well fertilised soil and the plant roots were allowed to grow into the lower compartment through a perforated bottom. The lower compartment was filled with an expanded clay substrate and nutrient solution, to supply the plants with water and all nutrients except P. The soil in the upper compartments was either dried [-W] or kept moist [+W] during a period of four weeks before harvest. The total plant P content did not differ significantly between the [-M] and the [+M] plants within the [+W] treatment. In contrast, the P content of the [+M] plants was almost twice as high as the [-M] plants when the soil in the upper compartment was dried. The concentrations of all elements except P in plant shoot tissue were sufficient for adequate plant growth. Phosphorus concentrations in the shoots of [-M/-W] plants indicated P deficiency, and these plants also had significantly lower dry matter and transpiration compared to the plants in all other treatments. From the results of the present experiment it can be concluded that mycorrhizal colonisation seems to be particularly benefical to P uptake from dry soil.