STOMATAL DEVELOPMENT AND SEASONAL CHANGES IN DIFFUSIVE RESISTANCE OF PRIMARY AND REGROWTH FOLIAGE OF RED OAK (QUERCUS RUBRA L.) AND RED MAPLE (ACER RUBRUM L.)

Abstract

SUMMARY From foliar emergence until senescence, the abaxial diffusive resistance of primary foliage, and of regrowth foliage produced after defoliation, was measured at several irradiances with a ventilated diffusion porometer. Concurrent measurements were made of stomatal dimensions and frequency, including scanning electron‐microscopy, and of leaf area. The diffusive resistance of newly emerged primary leaves was about 15 s cm−1 in maple and 20 s cm−1 in oak at all irradiances. The stomata became sensitive to light within 2 weeks of emergence, oak being slightly earlier than maple. Thereafter, the resistance at an irradiance of 0.5 cal cm−2 min−1 fell to a seasonal minimum of 3 s cm−1 in oak and 5–7 s cm−1 somewhat later in maple. With the onset of senescence, and earlier in maple than in oak, the resistance of primary leaves in bright light increased and the stomata became less sensitive to light. As leaf colour changed from green to red or brown, the resistance increased to about 60 to 80 s cm−1 in both oak and maple. The resistance of regrowth foliage that emerged in July was about 5–7 s cm−1 in maple and 12–15 s cm−1 in oak, thus lower than that in newly emerged primary foliage. Within a week of emergence, 3 weeks sooner than with primary foliage, the resistance at 0.5 cal cm−2 min−1 fell to about 3 s cm−1 in both species. During July and August, the resistance of regrowth foliage of maple was about one‐third that of the primary foliage, but about the same in both regrowth and primary foliage of oak. At the time of regrowth leaf emergence (July), the mean temperature was 10° C higher than that at primary leaf emergence (May), but in both species the initial rates of leaf expansion were similar. Although the areas of individual primary leaves were about twice those of regrowth leaves, the stomatal frequencies and dimensions were similar. Maximum stomatal length was achieved before the leaves were fully expanded and before the stomata became responsive to light. The development of light sensitivity was apparently independent of leaf expansion and the attainment of final stomatal size, but strongly dependent on environmental regulation of stomatal metabolism.

Changes in stomatal frequency, stomatal conductance and cuticle thickness during leaf expansion in the broad-leaved evergreen species, Eucalyptus regnans

“…Accordingly, many studies have suggested that changes in g s with leaf age are related to stomatal development, although few have directly related the two. Turner and Heichel (1977) observed that while diffusive resistance remained relatively constant, stomatal frequency first increased and then declined during leaf expansion in Quercus rubra L. and Acer rubrum L. Here, the decrease in stomatal frequency observed for young expanding leaves was counter to the progressive increase in g s . However, it should be noted that the total number of stomata per leaf remained fairly constant, and the number of mature stomata, with larger apertures, increased progressively, over the same period.…”

“…3a). Turner and Heichel (1977) noted that although the highest stomatal conductance was measured when surfaces of developing leaves were covered by profuse epicuticular waxes, the onset of wax occlusion later in the season coincided with a decrease in g s for Acer rubrum. In contrast, g s of young expanding leaves of E. regnans continued to increase during expansion (Fig.…”

“…While there have been numerous studies of leaf development in deciduous temperate (e.g. Choinski and Wise 1999;Federer 1976;Turner and Heichel 1977) and to a lesser extent, evergreen tropical trees (e.g. Woodall et al 1998), there are few studies in temperate broad-leaved species (but see Choinski et al 2003;Miyazawa et al 2003).…”

Diurnal courses and factorial dependencies of leaf conductance and transpiration of differently potassium fertilized and watered field grown barley plants

“…A decrease of g with age has been observed in many plants (e.g. tobacco: Vficlavik, 1974; broad-leaved trees: Turner and Heichel, 1977;bean: Minter, 1980;Pospis/lova and Sol~irovfi, 1984). The causal interpretation of this effect follows two lines.…”

Stomatal resistance of three potato cultivars as influenced by soil water status, humidity and irradiance

“…Atlantic probably had more senescing leaves. It has been shown that r s is less sensitive to Qp when leaves approach senescence than in fully expanded green leaves (Turner & Heichel, 1977;Vos & Oyarzun, 1987).…”