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XEROMORPHY INCREASES IN SHOOTS OF PSEUDOTSUGA MENZIESII (MIRB.) FRANCO SEEDLINGS WITH EXPOSURE TO ELEVATED TEMPERATURE BUT NOT ELEVATED CO2
Citation:
Olszyk, D M., M. Apple, B. Gartner, R. Spicer, C M. Wise, E. VanEss, A. Benson, AND D T. Tingey. XEROMORPHY INCREASES IN SHOOTS OF PSEUDOTSUGA MENZIESII (MIRB.) FRANCO SEEDLINGS WITH EXPOSURE TO ELEVATED TEMPERATURE BUT NOT ELEVATED CO2. TREES. Springer, New York, NY, 19:552-563, (2005).
Impact/Purpose:
To investigate changes in shoot organ structure, allometry and anatomy in response to simulated climate changes
Description:
Seedling structure influences tree structure and function, ultimately determining the potential productivity of trees and their competitiveness for resources. We investigated changes in shoot organ structure, as indicated by biomass allocation, allometry and anatomy in response to simulated climate changes, for seedlings of Pseudotsuga menziesii (Douglas-fir), a key Pacific Northwest tree species of the United States and Canada. Seedlings were grown under four climate change scenarios: ambient or elevated CO2 (+180 :mol mol-1) plus ambient or elevated temperature (+3.5 C) for four years in outdoor, sun-lit chambers. Biomass allocation and allometry were measured for buds, leaves, branches and stems, by age class. Woody tissue anatomy was evaluated in terms of stem wood density, specific conductivity, bark, wood and annual ring diameters, sapwood area, and leaf biomass / sapwood area ratio. Leaf anatomy was evaluated as cross-sectional area and perimeter, and by relative area of mesophyll cells, intercellular space, vascular tissues or resin canals.
Seedlings became more xeromorphic with elevated temperature. Allocation of total biomass to branches over stems and leaves increased and sapwood area to height ratio increased. The number of growing points relative to seedling size increased significantly (buds / total stem or branch length, and buds / branches). Stem and branch lengths and biomass decreased for sections initiated during the three full CO2 and temperature seasons. Total leaf area also tended to decrease, but not significantly. However, neither stem nor leaf anatomy was affected by elevated temperature. Increased xeromorphy of Douglas-fir shoots with elevated temperature likely resulted from alterations in biomass allocation among organs, bud morphogenesis, bud phenology, and stem and branch elongation.
Elevated CO2 increased specific weights of leaves (mg cm-2) and branches (mg mm-1 length), but had few other effects on shoot biomass allocation, allometry or anatomy. The effect of elevated CO2 on leaf density likely reflected changes in chemical composition . There were no CO2 x temperature interactions for any important parameter. Thus, under realistic simulated field environmental conditions (nitrogen and water limiting), the elevated temperature component, but not elevated CO2 component, of climate change may affect seedling shoot structure and, hence, future productivity and competitiveness of trees.