Document: JOH-3-30-26

The basis for co-variation in leaf lifespan and photosynthetic capacity: What is known and what is not.

SKILLMAN, J.B.* ^1,3, K.GRIFFIN ^2,3 and S.EARLL ^1,3

California State University, San Bernardino, CA 92407 USA ¹
Columbia University, Palisades, NY 10964 USA ²
Colombia University, Oracle, AZ 85623 USA ³

Abstract:
A negative association between leaf lifespan and photosynthetic capacity is known to exist among various plant species. This relationship indicates the existence of a tradeoff between these two determinants of plant productivity. Although this observed pattern encompasses a broad range of species, growth forms, and biomes, the fundamental processes leading to this tradeoff are unknown. The long-term objectives of this work are to identify physiological processes that may have led to this ecologically important pattern. In order to establish the parameters of this relationship for a set of plant species to be used in future experiments, we are characterizing aspects of the leaf demography and physiology for 40 species native to 4 different tropical habitats (wet forest, savanna-orchard, dry thorn-scrub forest, and tropical coastal strand). This investigation is being carried out in 4 different mesocosms at the Biosphere 2 Center. The use of this unique facility allows us to simultaneously study the ecophysiology of mature established plants of different species representative of different biomes. Preliminary results are qualitatively consistent with results from prior studies. At one extreme, Allamandra cathartica, (canopy vine from the rain forest), has a photosynthetic capacity of 21.4 10.2 mol CO₂ m^-2 s^-1 and an estimated foliar lifespan of 4.8 months. At the other extreme, Zamia fischeri, an understory Cycad in the rainforest, has a photosynthetic capacity of 1.6 0.6 mol CO₂ m^-2 s^-1 and an estimated foliar lifespan of 78 months. We interpret these findings in the context of several hypothesis by which metabolism and longevity may interact at the cellular and organismal levels.

Keywords: leaf longevity, photosynthesis, Biosphere2

This abstract is being presented at: 10:30 AM in session:
GAS EXCHANGE