Effects of environment, seedling age, and seed source on leaf resistance of three species of Chamaecyparis and Tsuga chinensis.

The objectives of this study were to determine how stomata of Chamaecyparis spp. react to environmental changes and to determine in what ways leaf resistance patterns may have adaptive value for these confers. Leaf resistances were measured of Chamaecyparis taiwanensis, C. formosensis and C. lawsoniana seedlings in a forest nursery, and of saplings of the first two species and Tsuga chinensis growing in natural forest and clearcuts. Light, temperature, humidity, and sometimes xylem pressure potential were measured concurrently.In the nursery, C. lawsoniana, the species from the driest climate, had the lowest resistance, daily means for well-watered yearold plants being 2-5 s cm-1. Leaf resistances of well-watered C. formosensis and C. taiwanensis from more humid habitats were two and three times greater. Leaf resistance was more sensitive to environment in those nursery populations of C. formosensis from habitats where a dry season is more severe. There were no clear patterns of variation within the other species. Resistance of scale leaves increased with seedling size and age. Primary leaves of C. formosensis had higher average resistance than its scale leaves, and were more responsive to changes in the environment.In the field, C. taiwanensis had higher resistance than C. formosensis. Leaf resistance of Tsuga chinesis was quite similar to that of C. formosensis. Resistance decreased from winter to spring except during a severe dry spell in March.Changes in leaf resistance were most consistently correlated with humidity, which often increased during the day as humid air rose from the lowlands. Stomata opened as humidity rose even when plant xylem pressure potentials were -15 to -23 bars. Stomatal reaction of Chamaecyparis spp. varies in ways apparently adaptive to their environment.