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Leaf Factors Affecting Light‐Saturated Photosynthesis in Ecotypes of Solidago virgaurea from Exposed and Shaded Habitats
Author(s) -
Holmgren Paul
Publication year - 1968
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1968.tb07293.x
Subject(s) - irradiance , photosynthesis , stomatal conductance , transpiration , botany , ecotype , biology , conductance , horticulture , photosynthetic efficiency , chemistry , physics , mathematics , quantum mechanics , combinatorics
Plants of Solidago virgaurea L. from exposed and shaded habitats differ with respect to the response of the photosynthetic apparatus to the level of irradiance during growth. An analysis was carried out on leaf characteristies which might be responsible for the differences established in the rates of Hght‐saturated CO 2 uptake. The clones were grown in controlled environment chambers at high and low levels of irradiance. Light‐saturated rates of photosynthesis and transpiration were measured at natural and lower ambient CO 2 concentrations. A low temperature dependence of light‐saturated CO 2 uptake at natural CO 2 concentrations, and a strong response to changes in stomatal width, suggested that the rate of CO 2 transfer from ambient air towards reaetion sites in chloroplasts was mainly limiting the pholosynthetic rate. Resistances to transfer of CO 2 for different parts of the pathway were calculated. There was a weak but significant correlation between stomatal conductance and the product stomatal frequency ± pore length. Mesopbyll conductance and dry weight per unit area were highly correlated in leaves not damaged by high irradiance. This suggests that mesophyll conductance increases with increasing cross sectional area (per unit leaf area) of the pathways of CO 2 transfer in the mesophyll from cell surfaces to reaction sites. The higher light‐saturated photosynthesis in clones from exposed habitats when grown at high irradiance than when grown at low irradiance was attributable mainly to a lower mesophyll resistance. In shade clones the effect upon CO 2 uptake of the increase in leaf thickness when grown at high irradiance was counteracted by the associated inactivation of the photosynthetic apparatus. The difference in CO 2 uptake present between clones from exposed and shaded habitats when preconditioned to high irradiance resulted from differences in both mesophyll and stomatal resistances. A few hybrid clones of an F 1 ‐population from a cross between a clone from an exposed habitat and a clone from a shaded habitat reacted, on the whole, in the same way as the exposed habitat parent. When grown at high irradiance, the hybrid clones showed higher photosynthetic rates than either parent; this was largely attributable to the unusually low stomatal resistance of the hybrid leaves.