Actually, evaporative cooling does not necessarily bring leaf temperature below ambient temperature. Because the leaf is absorbing light, it may be, say, 10 degrees warmer than the surrounding air. Depending on the details, the evaporative cooling may be able to bring this down only to perhaps 5 degrees WARMER than the surrounding air, or under other circumstances, perhaps 5 degrees COOLER than the air. As a generality, all we can say is that the evaporative cooling makes the leaf cooler than it would be if there were no evaporative cooling.
Martin M. Meiss 2012/4/17 Don Cipollini <[email protected]> > Malia, > > If I am reading your question correctly, any plant that is undergoing > evapotranspiration typically experiences evaporative cooling and will be > below ambient temperatures while this is occurring. Perturbations in this > effect, such as during drought-induced stomatal closure, can lead to heat > build-up and subsequent negative effects on photosynthesis. Whether > galling induces additional cooling effects beyond what is experienced by a > "normal" leaf experiencing evaporative cooling is unknown to me, but would > seemingly require some increase in evapotranspiration in galled leaves. > This might be expected for some gallers, but unexpected for others, > depending on hormonal changes in galled leaves (e.g. whether changes in > hormones like ABA would be expected). It would seemingly be adaptive for > gallers to help "cool" their host leaves, lest they be exposed to high > temperatures, while it might be adaptive for plants to bake their gallers > by locally reducing evaporative cooling in galled leaves. > > Don > > > On 4/17/2012 12:35 PM, R. Malia Fincher wrote: > >> I have been unsuccessfully (but briefly) searching the literature for >> incidences of plants and/or galls on plants cooling themselves >> substantially >> below ambient temperature. I have run across a fungal gall, with an >> associated gall midge larva, that is 6-10 degrees C colder than normal >> leaves and the ambient air temperature. I am aware of the capacity of >> certain plants to warm themselves, but this is the first time that I have >> encountered cooling. Is anyone familiar with such a phenomenon? >> >> Thank you, >> Malia >> >> R. Malia Fincher, Ph.D. >> Assistant Professor >> Samford University >> Department of Biological and Environmental Science >> 800 Lakeshore Drive >> Birmingham, Alabama35229 >> [email protected] >> 205-726-2928 >> Fax 205-726-2479 >> Office 133 Propst Hall >> >> > -- > ************************************* > Don Cipollini, Ph.D. > Professor- Plant Physiology/Chemical Ecology > Director- Environmental Sciences PhD Program > Department of Biological Sciences > Wright State University > 3640 Colonel Glenn Highway > Dayton, Ohio 45435-0001 > (937) 775-3805 > FAX (937) 775-3320 > email: [email protected] > Lab Page: > http://www.wright.edu/~don.**cipollini<http://www.wright.edu/%7Edon.cipollini> > Env Sci PhD Program: > http://www.wright.edu/**academics/envsci/<http://www.wright.edu/academics/envsci/> >
