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Drought is a major climate change concern for the Earth’s rainforests; however little is currently known about how these forests and individual plants will respond to water stress. At the individual level, the ability of plants to regulate their stomatal conductance is an important preservation mechanism that helps to cool leaves, regulate water loss, and uptake carbon dioxide. At the ecosystem level, transpiration in rain forests is a major contributor to the feedback loop that returns moisture to the atmosphere for continued rains. Nearly 60% of atmospheric moisture in the Amazon rain forests has been traced back to origins of transpiration from its plants. Under normal conditions, stomata conductance rates are highly variable across rainforest species; it is unknown to what extent these rates will decrease in response to water stress.
The University of Arizona’s Biosphere 2 (B2) served as the study site for a simulated 4-week long drought because of its ability to mimic the micrometeorology of an Amazonian rainforest. Three species of plants were chosen at various levels in the canopy: Clitoria racemosa, Cissus sicyoides, and Hibiscus elatus. These plants were selected based on their relative abundance in the B2 forest. It was revealed that two out of the three species exhibited decreases in H20 efflux at each elevation, while one species (C. racemosa) proved much more resistant, at each elevation, to H20 loss. These results may be useful in modeling how entire rainforest systems conserve, recycle, and lose water in connection to periods of drought.