Drought resistance of mycorrhizal pepper plants independent of leaf P concentration response in gas exchange and water relations.

by F.T. Davies, Jr, J.R. Potter and R.G. Linderman

Pepper (Capsicum annuum L.) plants with and without VA-mycorrhiza (formed by the fungus Glomus deserticola Trappe, Bloss & Menge), VAM, and NVAM, respectively, were drought acclimated (DA) by four drought cycles or kept well watered (NDA). All plants were the subjected to additional drought cycle, followed by a 3-day irrigation recovery period. Measurements of water relations gas exchange and carbohydrates were made at selected intervals throughout the drought cycles and recovery. To equalize growth and avoid higher P in VAM plants, NVAM plants received higher P fertilization. Consequently, similar transpirational surface and shoot mass were achieved in all treatments, but NVAM had a higher tissue P concentration than VAM plants. Plants that were either VAM or DA, but especially the VAM-DA plants, tended to be high in net photosynthetic flux (A), A per unit of tissue P concentration (A/P), stomatal conductance (g) or leaf turgor ( ) during high environmental stress or recovery from stress. During this time, NVAM-NDA plants had low A, A/P and leaf chlorophyll, but high soluble carbohydrate concentrations in their leaves. All VAM and DA plants had some osmotic adjustment compared to the NVAM-NDA plants, but VAM0DA had the most. Osmotic adjustment was not due to accumulation of soluble carbohydrate. The high turgor, A and g in the VAM-DA plants during and following environmental stress indicated superior drought recovery and cannot account for the observed drought resistance during environmental stress. Drought resistance of VAM-DA plants was not attributable to high leaf P concentration or confounded by differences in plant traspirational surface.

Physiologia plantarum 87: 45-53. Copenhagen 1993