Effects of photoperiod and moisture availability on shoot growth, seedling morphology, and cuticle and epicuticular wax features of container-grown western hemlock seedlings

Abstract

The influence of short-day and long-day photoperiods, and moderate drought stress (−1.0 MPa), all applied for 4 weeks beginning in mid-July, 1986, was studied on greenhouse-grown western hemlock (Tsugaheterophylla (Raf.) Sarg.) seedlings cultured in two Styroblock container cavity sizes. Shoot growth, morphology, and cuticle and epicuticular wax features were investigated. Weekly measurements of shoot growth were made from early June until growth cessation in October. Root collar diameter, shoot length, numbers of branches and needles, and needle lengths were recorded after shoot growth cessation in another subsample of trees. Shoot growth rapidly ceased under short days, whereas free growth continued under long days. Moisture stress had no effect on shoot growth phenology but significantly reduced final values for all morphological variables. The trends were similar in seedlings from both container sizes, but values were greater in those from the larger containers. Long days increased the total number of leaves and branches, especially under no moisture stress conditions. Under long days, stem unit and needle lengths were increased in the proximal portion of the shoot, whereas moisture stress alone reduced these values in the distal section of the shoot. Dormancy induction treatments had little effect on needle cuticle and epicuticular wax features, although fusion of wax rodlets in the stomata was less common under moisture stress conditions.