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Variations in sweetgum tree (Liquidambar styraciflua L) leaf ultrastructure after exposure to elevated CO2.
Nesbit, April*,1, Sholtis, Johnna1, Tissue, David1, 1 Texas Tech University, Lubbock, TX
ABSTRACT- The physiological and growth responses of trees to elevated CO2 are well documented, but considerably less is known about the effects of elevated CO2 on leaf ultrastructure. Recent studies with sweetgum trees have indicated that elevated CO2 may produce significant structural changes in cellular organelles, such as increased numbers of mitochondria per unit cell area and a greater proportion of stroma to grana thylakoids. These changes in cellular structure may reflect a shift in plant metabolism that partially explains enhanced plant growth in elevated CO2. Therefore, we measured the depth of different cell layers (epidermis, palisade parenchyma, mesophyll) within leaves of established sweetgum trees growing in ambient CO2 (~ 364 ppm) and elevated CO2 (~ 553 ppm) at the Oak Ridge National Lab Free-Air CO2 Enrichment (FACE) facility in eastern Tennessee. Preliminary data in the second year of CO2 treatment indicated that the number of palisade parenchyma cell layers increased in trees grown in elevated CO2. A more comprehensive study in the third year of CO2 treatment, in which leaf samples were collected in early- (May-June) and mid-growing season (July), indicated that neither CO2 treatment nor time of season affected the depth of different cell layers. However, leaf position within a branch significantly affected leaf ultrastructure. Leaves at the base of a branch had thicker palisade parenchyma cells (70%), spongy mesophyll cells (28%), and greater total leaf thickness (41%), as well as greater numbers of palisade cells per unit leaf area (17%), than did leaves at the tip of a branch. These results suggest that leaf position may play a larger role in controlling leaf ultrastructure than CO2 treatment.
KEY WORDS: Liquidambar styraciflua, ultrastructure