Tiny valves on the surfaces of leaves, called stomates, regulate carbon gain and water loss by plants, and are thus linchpins of the global carbon and water cycles. Amazingly, the same simple model regulates stomates worldwide. This model is backed by enormous empirical data and a 40-year-old evolutionary explanation, and controls carbon gain and water loss in all Earth System models that predict climate. It is one of the most widely accepted paradigms in ecology.
Nonetheless, neither the simple model nor the evolutionary hypothesis explains observed stomatal closure during drought. For this reason, climate modelers have been forced to add functions that close stomates in dry soils, which are unconstrained by data, and have been recently shown to be the dominant source of inter-model uncertainty about the functioning of carbon cycle. Moreover, the 40-year-old evolutionary hypothesis is not consistent with current understanding of plant competition for water, and does not include recent discoveries about damage to plant hydraulic systems during drought.
This seminar describes an alternative hypothesis that includes plant competition and hydraulic damage. The new hypothesis has the same empirical support as the classical hypothesis under non-drought conditions, predicts observed stomatal closure during drought, and closes one of the most important uncertainties in modeling the global carbon cycle.