PARENT SESSION
Poster Session #28: Gas Exchange.
Tuesday, August 6. Presentation from 5:00 PM to 6:30 PM. Exhibit Hall B & C, TCC

Drought constraints on leaf gas exchange by Miconia ciliata (Melastomataceae) in the understory of an eastern Amazonian regrowth forest.

Fortini, Lucas^*,1, Mulkey, Stephen¹, Zarin, Daniel¹, Vasconcelos, Steel², Carvalho, Claudio³, ¹ University of Florida, Gainesville, FL² Faculdade de Ciências Agrárias do Pará, Belém, PA, Brazil³ Embrapa Amazonia Oriental, Belém, PA, Brazil

ABSTRACT- We assessed the impact of drought on an abundant understory species (M. ciliata, Melastomataceae) by measuring leaf gas exchange and leaf water potential in irrigated and control plots in an eastern Amazonian regrowth forest during the 2001 dry-season. At the height of a dry spell, mean±se A_max values for the irrigation plots were substantially and significantly higher than A_max values for the control plots (4.33±0.304 v. 1.71±0.401 mol CO₂ m^-2 s^-1, p<0.0001). Stomatal conductance was similarly enhanced by irrigation (0.0602 v. 0.0158 mol H₂O m^-2 s^-1, p<0.001). Light response curves reinforced these results but failed to show clear differences in quantum yield efficiency and inflection points. Preliminary analysis of induction curves also suggests slower induction for drought-stressed control plants, which may hamper their utilization of short lasting sun flecks. Monthly leaf water potential measurements in irrigation and control plots indicate treatment differences in leaf gas exchange were strongly tied to moisture availability. Additionally, there was a major increase in leaf-level gas exchange exclusively in the control plots immediately following a dry season rain event (Amax = 1.72±0.172 mol CO₂ m^-2 s^-1, p<0.002). Our data indicate that in the absence of irrigation, A_max and conductance decline during the dry season limiting leaf carbon gain.

KEY WORDS: A_max, stomatal conductance, irrigation, dry season drought stress