Abstract
Nocturnal transpiration constitutes a significant yet poorly understood component of the global water cycle. Modeling nocturnal transpiration has been complicated by recent findings showing that stomata respond differently to environmental drivers over day- vs. night-time periods. Here, we propose that nocturnal stomatal conductance depends on antecedent daytime conditions. We tested this hypothesis across six genotypes of Eucalyptus camaldulensis Dehnh. growing under different CO2 concentrations (ambient vs. elevated) and exposed to contrasting temperatures (ambient vs. heat wave) for four days prior to the night of measurements, when all plants experienced ambient temperature conditions. We observed significant effects after the heat wave that led to 36% reductions in nocturnal stomatal conductance. The response was partly driven by changes in daytime stomatal behavior but additional factors may have come into play. We also observed significant differences in response to the heat wave across genotypes, likely driven by local adaptation to their climate of origin, but CO2 played no effect. Stomatal models may need to incorporate the role of antecedent effects to improve projections particularly after drastic changes in the environment such as heat waves.
Highlights
The opening of stomata during dark periods defies established conventions in both hydrology and plant physiology
To address the third question, we used different genotypes because we found genetic control of nocturnal stomatal conductance in this species [17] and, we expected differences based on the climate of origin
The heat wave was imposed in half of the plants after three months of growth, and air temperatures in the glasshouse were increased by 10 ◦ C for four days
Summary
The opening of stomata during dark periods defies established conventions in both hydrology and plant physiology. We sought to disentangle the possible effects of antecedent daytime conditions on nocturnal stomatal conductance by examining the response on the night immediately following a heat-wave event for genotypes of Eucalyptus camaldulensis grown in ambient and elevated CO2 concentrations. To understand how that impact would occur, we wanted to test three mutually compatible hypotheses: (i) stress from the heat wave affects overall stomatal behavior, including nighttime conductance, and day and night conductance would be correlated; (ii) heat-wave-induced changes in photosynthetic carbon assimilation correlate positively with nocturnal stomatal conductance (potentially via carbohydrate feedbacks); (iii) heat-wave-induced changes in daytime whole-plant transpiration correlate positively with nocturnal stomatal conductance (potentially through stem recharge). Previous studies have proposed examining responses across genotypes to increase the reproducibility of the results [18]
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