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DIFFERENCES IN LEAF STRUCTURE, CHLOROPHYLL, AND NUTRIENTS FOR THE UNDERSTORY TREE ASIMINA TRILOBA
Author(s) -
Young Donald R.,
Yavitt Joseph B.
Publication year - 1987
Publication title -
american journal of botany
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.218
H-Index - 151
eISSN - 1537-2197
pISSN - 0002-9122
DOI - 10.1002/j.1537-2197.1987.tb12140.x
Subject(s) - understory , biology , canopy , chlorophyll , botany , stomatal conductance , nutrient , photosynthesis , horticulture , chlorophyll a , ecology
To investigate differences in leaf structure, chlorophyll and nutrients on terminal branches of the understory tree Asimina triloba , the first (proximal) and the last (distal) leaves to develop in the spring were compared. Proximal leaf expansion was completed before the overstory canopy was fully closed but distal leaf expansion occurred during and after the development of the overstory canopy. Fully expanded proximal leaves were 76% smaller in area, were 18% thicker and had 36% more stomates per m of leaf area when compared to distal leaves. In addition, maximum stomatal conductance to water vapor was greater (150 vs. 120 mmol m −‐2 s −‐1 ) and the minimum PPFD required for maximum conductance was higher (200 vs. 150 μmol m −‐2 s −‐1 ) for the proximal leaves. Chlorophyll content was also greater for proximal leaves, but nitrogen and phosphorus contents were lower throughout the entire summer. Seasonal measurements indicated an increase in chlorophyll a content and reductions in nitrogen content throughout the summer growth period for leaves from both positions. The results suggest that distal and proximal leaves differed physiologically and that the measured differences were related to the changing irradiance environment during leaf development. The time of leaf expansion, as indicated by leaf position on the branch, may be an important consideration when examining the water and photosynthetic relations of understory trees.