The importance of multiple resource limitation to shade tolerance and habitat preferences in tropical and temperate tree saplings.
Published: 2005
Language: eng
Number of pages: 246
Description: Shade tolerance is typically reported as broad categories encompassing many species that are treated as ecological equivalents and is frequently considered from a single resource perspective: namely, ability to tolerate low light. However, variable soil resources and biotic factors also characterize the light-limited understory implying a role for multiple resource limitation in shade tolerance. In the present study, I quantified whole plant light compensation point (WPLCP) for saplings of tree species of varying shade tolerance from tropical and temperate systems using growth-, survival- and gas-exchange-based methods. Species traditionally classified as shade tolerant or light demanding were positioned at extreme and opposite ends of the shade tolerance continuum while mid-tolerant's WPLCP spanned the continuum. I measured morphological and physiological sapling traits to assess their contribution to WPLCP. In both tropical and temperate species, dark respiration (at the leaf or whole plant level) was a strong predictor of WPLCP. Seed size was also a strong predictor of gas-exchange based WPLCP. Using growth- and gas-exchange-based methods I examined changes in WPLCP with variable resources achieved through the experimentally manipulating light and nutrients. Nutrient addition generally had little effect on measured traits; however, gas-exchange-based WPLCP was higher in a number of temperate species under increased nutrients. Additionally, increased nutrient availability resulted in increased chlorophyll content and leaf-level spectral absorptance for some species, which could impact low-light carbon gain. In the tropical forest, comparisons were made between closely related species pairs occurring on two soil types differing in water and nutrient availability. Species associated with dry, sandy ridges showed conservative patterns of water use achieved at the cost of higher respiration rates in comparison to species associated with the moist, rich alluvial lowlands. WPLCP of species associated with the ridgetops were greater than alluvial specialists, likely due to the metabolic costs of higher water use efficiency given the contribution of respiration rates to WPLCP. In the temperate forest, site-to-site variation in water availability resulted in variable, species-specific responses of WPLCP, growth and leaf-level gas-exchange. These results provide strong evidence of multiple resource limitation and emphasize the importance of species' responses to soil resources in shade tolerance.
Notes: Advisor: Sean Thomas

Source: Dissertation Abstracts International, Volume: 66-10, Section: B, page: 5191.

Thesis (Ph.D.)--University of Toronto, 2005.

Electronic version licensed for access by U. of T. users.