Water relations, gas exchange and morphological development of fall- and spring-planted yellow cypress stecklings

Abstract

Yellow cypress ( Chamaecyparis nootkatensis (D.Don) Spach) stecklings (stock derived from rooted cuttings) were fall-(September 1990) and spring-planted (April, 1991) on a coastal reforestation site in British Columbia to determine the influence of planting season and various nursery cultural treatments on steckling establishment, growth and survival. Gas exchange and water relations measurements were made in the first year after planting, with morphological development monitored during the first and second year. A randomized complete block design (6 blocks) was used and influence of planting season was analyzed as an independent factor from the nursery cultural treatments. Nursery cultural treatment means within each plant-time population were similar ( t-test, α = 0.05), with no effect on steckling physiology during the first growing season. Moisture stress nursery cultural treatments produced smaller stecklings (e.g. shoot height, diameter, root and shoot dry weights) than well-watered treatments, but morphological differences disappeared after the first year. Water relation parameters indicated that fall-planted stock had greater turgor maintenance than spring-planted stock throughout the first growing season (e.g. fall ≥ spring in predawn and minimum shoot water potentials, total and utilized turgor; fall ≥ spring in osmotic potential at saturation and turgor loss point, and relative water content at turgor loss point). Spring-planted stecklings had greater maximum net photosynthesis under optimum conditions in a controlled environment, but had lower net photosynthesis under low air temperature conditions in the field, compared with fall-planted stecklings. Fall-planted stecklings had greater stomatal conductance under all measured field climatic conditions, except moderate conditions when both populations had similar stomatal conductance. Shortly after fall planting, extreme environmental conditions (i.e. soil surface temperatures of 42°C, evaporative demand > 4 kPa and steckling minimum shoot water potentials of − 1.61 ± 0.04 MPa) resulted in high fall-planted steckling mortality. As a result, survival rates measured 8 weeks after spring planting were 82.9% and 99.8% for fall- and spring-planted stecklings, respectively. Thereafter, spring planting, mortality was low and similar between the two plant-time populations. Fall-planted stecklings had greater root development early in the first growing season, but by season end, spring-planted stecklings had greater root development. At the end of the second growing season, both populations were similar in shoot development, though spring-planted stecklings had greater root development.