ALTERATION OF COMPONENTS OF LEAF WATER POTENTIAL AND WATER-CONTENT INVELVETLEAF UNDER THE EFFECTS OF LONG-TERM HUMIDITY DIFFERENCE

Velvetleaf (Abutilon theophrasti Medik.) was grown in growth chambers set at 45 or 85% relative humidity at 30-degrees-C, CO2 350 microliter s per liter and 1000 micromoles per square meter per second of photosy nthetically active radiation. Soil water potential was maintained at - 0.05 megapascal by subirrigation with half strength Hoagland solution. The third, fourth, and fifth leaves from the base of 21- and 25-day-o ld plants were used for pressure-volume measurements. Components of le af water status including water potential (osmotic and potential assoc iated with the apoplast), leaf water content (apoplasmic and symplasmi c water), and elastic modulus of leaf tissue were determined. Results indicate: (a) persistent dry air generated leaves with lower water pot ential at a given relative water content than did humid air; (b) the h igher total leaf water content in plants grown in dry air was related to an increase in apoplasmic water, whereas symplasmic water remained similar in both humidity treatments; (c) difference in leaf water pote ntial between low and high humidity treatments was related to decrease d potential associated with the apoplast but not to a change in cell w all elasticity.