WATER-STRESS, TEMPERATURE, AND LIGHT EFFECTS ON THE CAPACITY FOR ISOPRENE EMISSION AND PHOTOSYNTHESIS OF KUDZU LEAVES

Kudzu (Pueraria lobata (Willd) Ohwi.) is a vine which forms large, mon ospecific stands in disturbed areas of the southeastern United States. Kudzu also emits isoprene, a hydrocarbon which can significantly affe ct atmospheric chemistry including reactions leading to tropospheric o zone. We have studied physiological aspects of isoprene emission from kudzu so the ecological consequences of isoprene emission can be bette r understood. We examined: (a) the development of isoprene emission as leaves developed, (b) the interaction between photon flux density and temperature effects on isoprene emission, (c) isoprene emission durin g and after water stress and (d) the induction of isoprene emission fr om leaves grown at low temperature by water stress or elevated tempera ture. Isoprene emission under standard conditions of 1000 mumol photon s . m-2 . s-1 and 30-degrees-C developed only after the leaf had reach ed full expansion, and was not complete until up to two weeks past the point of full expansion of the leaf. The effect of temperature on iso prene emission was much greater than found for other species, with a 1 0-degrees-C increase in temperature causing a eight-fold increase in t he rate of isoprene emission. Isoprene emission from kudzu was stimula ted by increases in photon flux density up to 3000 mumol photons . m-2 . s-1. In contrast, photosynthesis of kudzu was saturated at less tha n 1000 mumol . m-2 . s-1 photon flux density and was reduced at high t emperature, so that up to 20% of the carbon fixed in photosynthesis wa s reemitted as isoprene gas at 1000 mumol photons . m-2 . s-1 and 35-d egrees-C. Withholding water caused photosynthesis to decline nearly to zero after several days but had a much smaller effect on isoprene emi ssion. Following the relief of water stress, photosynthesis recovered to the prestress level but isoprene emission increased to about five t imes the prestress rate. At 1000 mumol photons . m-2 . s-1 and 35-degr ees-C as much as 67% of the carbon fixed in photosynthesis was reemitt ed as isoprene eight days after water stress. Leaves grown at less tha n 20-degrees-C did not make isoprene until an inductive treatment was given. Inductive treatments included growth at 24-degrees-C, leaf temp erature of 30-degrees-C for 5 h, or withholding water from plants. Wit h the new information on temperature and water stress effects on isopr ene emission, we speculate that isoprene emission may help plants cope with stressful conditions.