Abstract Detail


Garnica Diaz, Claudia Juliana [1], Machado, Siddarth [2], Castillo-Argaez, Raiza [3], Smith, Nicholas Ash [3], Johnson, Daniel J. [2], John, GRACE PATRICIA [3].

Intra-canopy leaf variation in deciduous oaks (genus Quercus): from leaf construction to energy return.

The leaf economic spectrum (LES) is a framework used to explain coordination of leaf structure and metabolism. According to the LES, trade-offs between resource acquisition and carbon investment limit trait covariation forming a single unified axis of fast vs slow return. Yet, most studies employing the LES follow a sampling protocol that focuses on outer canopy leaves while ignoring variation through canopy positions (CP). As much of the vegetation comprising the world’s forests persists in shade, characterization of sun-exposed leaves may not represent processes at the canopy or community scale. Here, we characterized the impacts of the light on leaf structure across canopy positions and evaluated their functional implications on photosynthetic light responses and water relations. we sampled branches from sun-exposed and shaded parts of 30 canopy trees across five deciduous oak species in the ForestGEO plot at Lilly-Dickey Woods, Indiana. As oaks have expressed large variation in their leaf morphometrics in previous studies, we predicted that sun-exposed leaves would have more complex morphology and thicker lamina demanding construction costs. However, contrary to expectations from the LES, sun-exposed leaves would also have faster maximum rates of energy return due to greater investment in photosynthetic machinery.
While all our structural and compositional traits varied significantly across species and CP, traits associated with an investment in photosynthetic area (i.e., leaf area, perimeter, and shape) varied more based on species, than position. In contrast, the CP explained most of the variance (between 25% and 50%) of traits associated with investment in structural support (i.e., leaf mass per area [LMA], dry matter content [LDMC], and thickness [Lt]). In sun-exposed parts of the canopy, trees invested in tougher leaves with higher LMA and Lt (p-value<0.001), corresponding to the slow-return end of the LES, suggesting intra-canopy shifts driven primarily by a change in structure, rather than composition. Similarly, shaded leaves were associated with a lower investment in structural support and greater investment in projected area. Structural changes did not induce a significant change in maximum photosynthetic assimilation on a mass or area basis. The convergence of Amax across the canopy may arise due to shifts in dark respiration and light compensation point such that leaves in the sun are associated with a greater metabolic maintenance cost requiring higher irradiance to achieve photosynthetic gains. Notably, sun-exposed leaves also maintained lower turgor loss points [tlp] (p-value<0.001), such that a larger proportion of the variation in tlp was explained by CP than by species. As sun-exposed canopies experience higher temperatures and greater osmotic stress, the shift in tlp is likely a mechanism to maintain open stomata for evaporative cooling and gas exchange. As in Amax, the manipulation of stomatal behavior conferred by differences in tlp enabled the maintenance of similar leaf relative water content [RWC] and water potential [MDWP] across CPs The coordination of investment in photosynthetic machinery, structural support, and high osmotic potentials allow trees to maximize carbon assimilation and water status across light environments within the canopy outside of the constraints of LES tradeoffs.

1 - University of Florida, Biology, 876 Newell Dr, Bartram Hall 310, Gainesville, FL, 32611, United States
2 - University of Florida, School of Forest, Fisheries and Geomatics Sciences, 118 Newins-Ziegler Hall, Gainesville, Florida, 32603, United States
3 - University of Florida, Biology, 876 Newell Dr, Bartram Hall 310, Gainesville, Florida, 32611, United States

economic spectrum
wilting point

Presentation Type: Oral Paper
Number: EPH2007
Abstract ID:624
Candidate for Awards:Physiological Section Physiological Section Li-COR Prize,Physiological Section Best Paper Presentation

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