Abstract Detail

Ecophysiology

Momayyezi, Mina [1], McElrone, Andrew [2].

Structural and functional leaf diversity lead to differences in photosynthetic capacity across Juglans regia accessions.

Leaves balance CO₂ exchange and water transport across their tissues to optimize photosynthesis. CO₂ diffusion through mesophyll (mesophyll conductance, g_m) and fixation at the carboxylation sites depend on a series of complex leaf features. Differences in leaf structural and functional characteristics explain net assimilation rate (A_n) and associated responses to the environment under inherent and induced conditions. In walnut nut production, only a few Juglans regia cultivars are dominantly used as scions, and this raises concerns about the low genetic diversity and high risk of susceptibility to abiotic and biotic stressors. In this study we explored the anatomical and biochemical bases of photosynthetic capacity in 11 J. regia accessions collected from the USDA-National Clonal Germplasm Repository at the University of California Davis, with distinct genetic divergence and originating from different latitudes with varying temperature and precipitation gradients. Using X-ray microcomputed tomography, we found a parallel shift in mesophyll thickness and porosity concurrent with gas exchange responses in J. regia accessions. A_n was greater in lower latitudes concurrent with increases in stomatal conductance and g_m. Leaves with higher A_n were thicker having greater mesophyll porosity, but showing less leaf mass per area (LMA). Greater nitrogen content per area (leaf N) in those leaves suggests a higher biochemical activity as a trade-off for the reduced mesophyll cell packing. Consistent with A_n observations (at 400 ppm CO₂), the CO₂-saturated assimilation rate (A_max) (at 1400 ppm CO₂) was also correlated with greater mesophyll thickness, porosity, and leaf N. Higher porosity and intercellular airspace conductance were associated with lower stomatal density. Greater A_n was found in accessions native to climates with more frost-free days and precipitation seasonality but lower temperature seasonality in lower latitudes. Even under dehydration, A_n, g_m, and porosity remained higher for low-latitude accessions. We suggest that J. regia accessions originated from lower latitudes, having distinct leaf structural traits with greater CO₂ diffusivity in co-existence with enhanced biochemical capacity, can be used as commercial walnut scions or breeding parents for greater productivity and enable development of future accessions with improved stress tolerance.

1 - Boise State University, Snake River Plains Herbaria, , Boise, Idaho, 83725, USA
2 - University of California Davis, 2154 RMI North, Department of Viticulture & Enology Department, University of California Davis, Davis, California, 95616, United States

Keywords:
leaf anatomy
photosynthetic capacity
functional diversity
Juglans regia
geographic distribution.

Presentation Type: Oral Paper
Session: ECOPH1, Ecophysiology I
Location: /
Date: Monday, July 19th, 2021
Time: 10:45 AM(EDT)
Number: ECOPH1004
Abstract ID:903
Candidate for Awards:None