Foliar dehydration tolerance of mycorrhizal cowpea, soybean and bush bean

Foliar dehydration tolerance of three mycorrhizal and nonmycorrhizal legume s is presented here. Leaf water potential, osmotic adjustment and soil matric potential at the e nd of a lethal drying episode were compared in soybean, cowpea and bush bea n colonized or uncolonized by Glomus intraradices. Lethal leaf water potential were similar among treatments except in soybean , for which nonmycorrhizal plants given low phosphorus fertilization had va lues 0.3-0.4 MPa lower than mycorrhizal plants or nonmycorrhizal plants giv en higher phosphorus fertilization. Mycorrhizal symbiosis did not affect os motic adjustment or lethal soil matric potential. Nonmycorrhizal cowpeas gi ven low phosphorus showed more osmotic adjustment than nonmycorrhizal cowpe as given higher phosphorus. Foliage of host species typically classified as drought avoiders, cowpea and bush bean, survived to lower soil matric pote ntials than soybean, although soybean foliage was more tolerant of dehydrat ion. Our findings support the idea that when arbuscular mycorrhizal plants fare better than nonmycorrhizal plants during drought, it is probably due to enh anced drought avoidance capabilities conferred by the symbiosis rather than to changes in ability of foliage to withstand dehydration.