Abstract Detail


Momayyezi, Mina [1], Borsuk, Aleca [2], Brodersen, Craig [3], Gilbert, Matthew [4], Theroux-Rancourt, Guillaume [5], McElrone, Andrew [6].

Leaf anatomy links CO2 diffusion and light absorption under inherent and drought-induced conditions in two walnut species.

Leaves must effectively absorb both CO2 and light and maintain water delivery to maximize photosynthetic efficiency. Fixation of the CO2 molecules that diffuse to carboxylation sites is highly dependent on the efficiency of the light absorption in mesophyll cells through the leaf profile. In this study, we evaluated how dehydration impacts these processes through changes in leaf structure and function in two important walnut species, Juglans regia and J. microcarpa, with varying leaf anatomy. We investigated inherent anatomical and biophysical traits and drought-induced changes in association with gas exchange, mesophyll conductance (gm) and optical properties through leaf profiles. X-ray microcomputed tomography (micro CT) imaging showed inherent differences between the species. J. regia exhibited thicker leaves with a larger mesophyll layer and greater porosity associated with lower packing of cells that were concentrated towards the adaxial epidermis; this coincided with greater intercellular air space conductance (gIAS), gm, stomatal conductance (gs), photosystem II efficiency, and net photosynthesis (An) compared to J. microcarpa. Water stress decreased leaf and mesophyll thickness and cell packing and increased porosity similarly for both species, which coincided with equivalent reductions in gm and gs in both species but a larger decrease in An and leaflet hydraulic conductance (Kleaflet) for J. microcarpa. The reduction in An under dehydration in J. microcarpa was more strongly tied to stomatal limitation as it was reversible at saturating CO2, but reductions in An were irreversible at high CO2 for J. regia. Chlorophyll distribution determined from fluorescence under epi-illumination of leaf cross sections was different between the species with J. regia exhibiting higher relative fluorescence in upper mesophyll, while the distribution for J. microcarpa was more consistent across the profile. Water stress induced species-specific changes in the location and magnitude of absorption peaks across the leaf profile that were associated with changes in cell geometry and intercellular air space (IAS) detected with microCT. Increases in porosity and gIAS under dehydration could not overcome loss of photosynthetic capacity suggesting they are not critical components on driving the photosynthetic responses to water stress.

1 - University of California Davis, 2112 RMI North, Department of Viticulture & Enology , University of California, Davis, Davis, California, 95616, United States
2 - Yale School of the Environment, 370 Prospect Street, Greeley Memorial Laboratory, New Haven, Connecticut, 06511, United States
3 - Yale University, School Of Forestry & Environmental Studies, 195 Prospect Street, Kroon Hall, New Haven, CT, 06511, United States
4 - University of California Davis, 2314 PES, UC Davis, One Shields Ave, Davis, California, 95616, United States
5 - University of Natural Resources and Life Sciences, Vienna, Institute of Botany (Botany), MENH-EG/30.3- Gregor-Mendel-Stra├če 33 1180 Vienna, Vienna, 1180 Wien, Austria
6 - University of California Davis, 2154 RMI North, Department of Viticulture & Enology Department, University of California Davis, Davis, California, 95616, United States

Leaf anatomy
Mesophyll conductance
Light absorption
Mesophyll porosity
Micro CT scanning

Presentation Type: Oral Paper
Session: PHYS2, Physiology II
Location: Virtual/Virtual
Date: Tuesday, July 28th, 2020
Time: 4:00 PM
Number: PHYS2005
Abstract ID:835
Candidate for Awards:Physiological Section Physiological Section Li-COR Prize,Physiological Section Best Paper Presentation

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