Drought avoidance in Katsura by drought-induced leaf abscission and rapid refoliation

The limited use of the katsura tree (Cercidiphyllum japonicum Sieb, & Zucc. ) in the landscape may be due to its reputed, but uncharacterized, intolera nce of drought, We examined the responses of katsura trees subjected to epi sodes of drought. Container-grown trees in a greenhouse were subjected to o ne of three irrigation treatments, each composed of four irrigation phases. Control plants were maintained under well-hydrated conditions in each phas e. Plants in the multiple-drought treatment were subjected to two drought p hases, each followed by a hydration phase. Plants in the single-drought tre atment were exposed to an initial drought phase followed by three hydration phases. Trees avoided drought stress by drought-induced leaf abscission, P lants in the multiple- and single-drought treatments underwent a 63% and 34 % reduction in leaf dry weight and a 60% and 31% reduction in leaf surface area, respectively. After leaf abscission, trees in the single-drought trea tment recovered 112% of the lost leaf dry weight within 24 days. Leaf absci ssion and subsequent refoliation resulted in a temporary reduction in the l eaf surface area : root dry weight ratio. After relief from drought, net as similation rate and relative growth rate were maintained at least at the ra tes associated with plants in the control treatment. We conclude that katsu ra is a drought avoider that abscises leaves to reduce transpirational wate r loss, Although plants are capable of refoliation after water becomes avai lable, to maintain the greatest ornamental value in the landscape, siting o f katsura should be limited to areas not prone to draught.