Leaf growth and development in relation to gas exchange in Quercus marilandica Muenchh.

Photosynthesis, transpiration rates and stomatal conductances were measured using a portable infra-red gas analyzer and then correlated with structural changes occurring during the development of Quercus marilandica Muenchh. leaves. Q. marilandica was found to synthesize high levels of leaf anthocyanins (0.79 +/- 0.13 gkg(-1) fresh weight) during the period immediately following bud break. Carbon assimilation rates showed net respiration (-1.3 +/- 1.6 mu mol m(-2) s(-1)) when measured in anthocyanin-containing leaves seven days after bud break (DAB), but to be near the compensation point at 17 DAB (1.1 +/- 1.4 mu mol m(-2) s(-1)) when most of the anthocyanins were metabolized away, but the leaves not yet fully expanded. The maximum rate (8.3 +/- 2.6 mu mol m(-2) s(-1)) was observed in fully expanded leaves at 37 DAB and was eight-fold higher than at 17 DAB. Transpiration rates and stomatal conductances were low at 7 DAB, bur then increased 250 and 160 %, respectively, at 17 DAB, but only 22 and 43 % from 17 to 37 DAB. Ultrastructural analysis showed the leaves had small intercellular air spaces and underdeveloped chloroplasts at both 7 and 17 DAB; the leaves not appearing fully mature until expansion was complete at 37 DAB. SEM images showed 7 DAB leaves to be extensively covered with trichomes on both abaxial and adaxial surfaces. The trichomes were mostly shed by 17 DAB revealing the extensive development of stomates. It is concluded that transpiration and stomatal conductances were controlled primarily by the boundary layer resistance associated with the trichome layer at 7 DAB and the low carbon assimilation rates seen at 17 DAB were likely a consequence of sub-optimal chloroplast function and/or limitations in CO2 uptake associated with the lack of intercellular air spaces.