Environmental influences on the development of spruce needle cuticles

Seedlings of Norway [Picea abies (L.) Karst.], red (P. rubens Sarg.), black [P. mariana (Mill) B.S.P.] and white [P. glauca (Moench.) Voss] spruce were grown from bud break to bud set outdoors, in the greenhouse, and in controlled environment chambers. The outdoor and greenhouse treatments also included adjacent shaded (50%) seedlings. The effects of growth environment on needle epicuticular wax production and morphology, and on needle wettability were investigated. Red and black spruce exhibited free growth in addition to determinate growth, but only in the greenhouse. Although relative growth rate was significantly lower for seedlings grown outdoors, there were no differences in wax morphology between outdoor- and greenhouse-grown seedlings, Wax deposits on controlled environment seedlings were significantly more crystalline. Wax tubes were crystallized in 'tufts'. There were significant differences in wax amounts recovered between species and treatments. Wax amounts relative to needle dry weights decreased in the order greenhouse > outdoors > controlled environment. Shaded red and black spruce produced significantly more wax than unshaded. Needles from seedlings grown in controlled environment chambers had the largest needle/droplet contact angles. These data indicate that seedling growth environment affects needle epicuticular wax characteristics and wettability. Studies designed to investigate factors determined by needle surface phystcochemical characteristics should include a consideration of growth environment.