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Mycorrhizal and non-mycorrhizal tomato plants (Lycopersicon esculentum Mill. cv 'Amalia') were subjected to water stress by withholding irrigation water for 72 hours and then reirrigated for 120 hours. Water stress reduced root mycorrhizal colonization, although the presence of the fungus Glomus clarum stimulated tomato plant growth. During the stress period the effect on the growth was more pronounced in aerial biomass than in the root biomass. The decrease in the soil water potential generated a decrease in leaf water potential (Psi(1)) and leaf turgor potential (Psi(t)), particularly in the non-mycorrhizal plants. Although the absence of osmotic adjustment provoked the loss of turgor in stressed plants, both Psi(1) and Psi(t) recovered after a short reirrigation period. Mycorrhizal infection improved photosynthetic activity (P-n) and stomatal conductance (g(s)) in non-stressed and stressed plants. These increases were accompanied by higher root hydraulic conductivity values, indicating enhanced water uptake in drought conditions. Neither P-n nor g(s) fully recovered after rewatering. The beneficial effect of the mycorrhizal symbiosis on the water status of tomato plants stimulated plant growth.
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