Observed and modelled stomatal responses to dynamic light environments in the shade plant <i>Alocasia macrorrhiza</i>

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<jats:p><jats:bold>Abstract.</jats:bold> Dynamic responses of stomatal conductance to lightflecks (15 s to 5 min) were observed in the tropical understory plant <jats:italic>Alocasia macrorrhiza.</jats:italic> Brief observations were also made on step changes in light, flashing light and short low‐light periods (darkflecks) after stomata had reached steady state conductances in high light. Stomata opened substantially even in response to very short lightflecks, with maximal opening being reached about 20 min after the end of the lightfleck. These responses are compared to those of a semi‐mechanistic stomatal model consisting of three steps in series: a biochemical signal which responds directly to light, producing osmotic changes within the guard cells which, in turn, drive the movement of water into the guard cells. The rate of change of each component was assumed to be given by the difference between the current state of that component and the state of the previous component in the series divided by a characteristic time constant for each step. This model allowed excellent description of observed responses to lightflecks, including the fleck‐length dependence of stomatal opening, the lag between the end of the lightfleck and the time of maximal stomatal conductance and the response to multiple flecks. However, agreement with predicted responses to flashing light and darkflecks was poor. Good agreement could be restored by using different time constants for the initial biochemical step, suggesting that the speed of the initial biochemical response is not constant but dependent on the current physiological state of the stomata. For leaves experiencing predominantly low light, punctuated by relatively short and infrequent periods of high light, this model allows good description of the dynamic changes in stomatal conductance.</jats:p>

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