Abstract Detail

Physiology

Ochoa, Marissa E [1], Sack, Lawren [2], Buckley, Thomas N [3], Henry, Christian [4], Medeiros, Camila [4], Pan, Ruihua [5], John, GRACE PATRICIA [6].

How does stomatal anatomy influence leaf conductance from minimum to maximum? Causal relationships and meta-analysis.

For well-watered plants, photosynthetic and transpiration rates are strongly determined by the amount of open stomatal pore which determines stomatal conductance to water vapor and CO₂. Even under severe drought, when stomata are closed, further water loss occurs, due to a nonzero leaf minimum epidermal conductance (g_min) arising from the permeability of the cuticle and incompletely closed stomata. While the role of stomatal traits, such as density and size, on stomatal conductance when stomata are open maximally, or partially during typical operation (g_max and g_op respectively) have long attracted attention, their role in determining g_min is gaining interest as drought events become more common and severe in many locations around the globe. Given stomatal closure during drought g_min plays a key role in determining leaf and plant dehydration rates and potentially mortality. Recent controversy has arisen concerning the dependence of g_min on stomatal traits, with some suggesting that species with high g_max and g_op also have high g_min, reducing their drought tolerance. To test the relative constraints of g_max, g_op and g_min by stomatal anatomy, we derived new equations for the biophysical determinants of stomatal conductance, from full opening under optimal conditions, to minimum aperture, and enabling calculation of the minimal stomatal aperture of the closed guard cells (a_min). This approach enables the causal partitioning of the influences on g_min of stomatal density, size, cuticular conductance, and minimal stomatal aperture (a_min). We partitioned the causes of g_min from novel and published data from 7 studies of 86 diverse species for g_min and anatomical traits. Only 2 of 7 studies showed correlations of g_min with stomatal density and size. Causal analyses showed that on average g_max and g_op but not g_min showed strong determination by stomatal density and not on stomatal size. g_min was causally driven by cuticular permeability, and a_min, which across species was independent of stomatal density and size and of maximum aperture. Our findings explain why drought tolerant species often have high stomatal densities, to enable rapid gas exchange in periods when water is available, without intrinsic cost in a high g_min, and point to the minimum stomatal aperture, cuticular permeability and water storage capacitance as critical determinants of leaf and plant drought survival.

1 - University of California, Los Angeles, Department of Ecology and Evolutionary Biology, 612 Charles E. Young Drive South, 101 Hershey Hall, Box 957246, Los Angeles, CA, 90095, USA
2 - 621 Charles E. Young Drive South, Los Angeles, CA, 90095, United States
3 - University of California, Davis, Department of Plant Sciences, College of Agricultural and Environmental Sciences, One Shields Avenue, Davis, CA, 95616, United States
4 - University of California, Los Angeles, 612 Charles E. Young Drive South, 101 Hershey Hall, Box 957246, Los Angeles, CA, 90095, United States
5 - Inner Mongolia University, School of Ecology and Environment, 235 Daxue West Street, Hohhot, Inner Mongolia, 010021, China
6 - University of Florida, Biology, 876 Newell Dr, Bartram Hall 310, Gainesville, Florida, 32611, United States

Keywords:
physiology
minimum cuticular conductance
Oaks
gmin
Stomata.

Presentation Type: Poster
Number: PPS004
Abstract ID:763
Candidate for Awards:Physiological Section Physiological Section Li-COR Prize