PARENT SESSION
Poster Session 2: Forest Ecology
Monday, August 8, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal

Effects of water stress on photosynthesis and water use efficiency in American chestnut.

Bauerle, William^*,1, Wang, G. Geoff¹, Bowden, Joseph¹, Hong, Christina², ¹ Clemson University, Clemson, SC, USA² Governors School of Math and Science, Hartsville, SC, USA

ABSTRACT- With the anticipated reintroduction of blight resistant American chestnut (Castanea dentata [Marsh.] Borkh.), it is important to decipher physiological responses of the species to climate conditions that are expected to prevail in upcoming decades. We tested the hypothesis that water use efficiency of American chestnut seedlings is increased by water stress. Seedlings were exposed to water deficits and their physiological responses were investigated under glasshouse and field conditions. Gas exchange, leaf optical properties, and growth were measured on well-watered and drought stressed seedlings. Under well-watered conditions, field grown seedlings had consistently higher A_net and g_s values than glasshouse seedlings. Under conditions of low soil water availability, both field and glasshouse grown seedlings responded with a general increase in instantaneous water use efficiency (WUI_i). The results suggest that American chestnut can overcome precipitation shortfalls that may become more prevalent in the future. Compared to well-watered conditions, drought stress significantly reduced the amount of light absorption regardless of growth environment. Under well-watered conditions, both field and glasshouse grown seedlings had different but similar maximum net photosynthesis rate (A_max) and maximum rate of ribulose 1,5 bisphosphate regeneration (J_max); however, maximum carboxylation (Vc_max), CO₂ compensation point (), carboxylation efficiency (CE), and dark respiration (R) were substantially higher in the field grown seedlings. We conclude that American chestnut has a preadaptation to water stress that might be a key survival determinant for its reintroduction into an environment where water stress may become more prominent.

Key words: leaf conductance, net photosynthesis, water-use efficiency