Document: COL-3-34-55

Stomatal response to elevated CO₂ changes with seasonal water availability in pinyon pine and juniper.

EDGAR, C.W.* and G.W.KOCH

Northern Arizona University, Flagstaff, AZ, U.S.A. ¹

Abstract:
Elevated carbon dioxide (CO₂) levels are reported to reduce stomatal conductance (g_s) in many plants, potentially decreasing water stress. Despite its significant role in determining future ecosystem water and carbon balance, data on the conductance response of woody species is relatively scarce. Water-use strategies often vary among dominant woody species; therefore, physiological differences may result in differential impacts on water use under elevated CO₂. This study examined two cooccurring tree species, Pinus edulis and Juniperus monosperma, which differ in drought tolerance and transpirational patterns. In contrast to J. monosperma, P. edulis has been shown to be less drought tolerant and exhibits higher water use efficiency (WUE). We measured the leaf-level g_s response of each species to one-hour increases (1.5times ambient) in CO₂ during the growing season. This short-term CO₂ increase was designed to measure the initial stomatal response in the field. During late June and July, prior to summer rain events, high CO₂ resulted in g_s reductions of 8.6% and 24.7% in P. edulis and J. monosperma, respectively. However, in September, after heavy rains, changes in g_s under high CO₂ were attenuated; +0.31% in P. edulis and -6.0% in J. monosperma. Because stomatal closure under high CO₂ was enhanced during periods of lower soil moisture, we suggest that reduction in g_s may best benefit WUE under drier conditions. Perhaps P. edulis shows less overall stomatal response to high CO₂ due to its inherently greater WUE.

Keywords: water use efficiency, elevated carbon dioxide, Pinus edulis, Juniperus monosperma

This abstract is being presented at: 4:30 PM in session:
Oral Session #30: Effects of Elevated Carbon Dioxide.