Raymund S. Folk

Determining field performance potential with the use of limiting environmental conditions

An operational assessment of stock quality, prior to field planting, usually includes measures of morphology and a test for root growth capacity (RGC) conducted under optimum conditions. When measured under optimum conditions and interpreted with regard to seedling phenology, performance attributes, such as RGC, provide valuable information about the “functional integrity” of stock at the time of measurement. However, reforestation sites are rarely associated with optimum growing conditions, and performance attributes measured under optimum conditions provide limited information about field performance potential. Due to these limitations, testing programs at the Forest Biotechnology Centre (BCRI) have used limiting environmental conditions to represent the planting site. This concept is based on the philosophy that tests under limiting environmental conditions will define seedling tolerance and/or resistance to conditions that prevail on the planting site, and hence, better forecast field performance potential. Evidence supporting this concept is presented in three case studies and other cited studies, where performance attributes were measured under a range of limiting environmental test conditions. A performance attribute response model is then presented to define the relationship between testing conditions and field performance potential forecasting. Applicability of this testing approach to operational reforestation programs is discussed.

Gas exchange, water relations and morphology of yellow-cedar seedlings and stecklings before planting and during field establishment

Information is lacking on how yellow-cedar (Chamaecyparis nootkatensis (D. Don.) Spach) stecklings compare with seedlings in their response to potentially limiting field site environmental conditions. Before planting, yellow-cedar seedlings and stecklings were characterized at 5 and 22°C root temperatures for gas exchange parameters (n=6), root growth capacity (n=12) and plant water movement (n=6) using a fully randomized design in a controlled environment growth room. Seedlings, compared with stecklings (t-test), showed a faster (p=0.01) recovery of net photosynthesis (Pn) and stomatal conductance (gwv) after root temperature increased from 5 to 22°C. Seedlings had greater (p=0.05) root growth capacity (number of new roots ≥ 0.5 cm in length) than stecklings after 14 days at 22°C and after 14 days at 5°C followed by 15 days at 22°C. Seedlings had a lower (p=0.01) resistance to plant water movement measured after 29 days (14 days at 5°C followed by 15 days at 22°C root temperature).Seedlings and stecklings were planted on a coastal British Columbia field site and monitored for 1) morphological development and physiological response to ambient site conditions throughout the first growing season, and 2) physiological response to drought conditions during late summer. Both trials used a fully randomized design and stock type means were compared using t-tests (p=0.10, 0.05, and 0.01). Initially, seedlings were taller (p=0.01) than stecklings but otherwise morphologically similar (n=20). Over a 35 week period after planting, stecklings had greater incremental height growth, while seedlings produced a greater (p=0.01) number of roots extending out of the root plug. Seedlings and stecklings (n=6) had similar Pn and gwv patterns under late spring environmental conditions. However, seedlings had greater Pn and gwv under cold temperature (p=0.05 and p=0.1, respectively) and drought conditions (p=0.05 and p=0.01, respectively), but during conditions of high evaporative demand and adequate soil moisture, stecklings had greater (p=0.01) Pn and gwv. Seedlings had higher (p=0.01) daily integrated shoot water potential values (Dψ) at different times during the growing season, and maintained higher (p=0.05) predawn (ψpd) shoot water-potential values, higher (Dψ) (p=0.01) and lower (p=0.01) resistance to plant water movement (RSPAC) during drought conditions.

Stock-type patterns of phosphorus uptake, retranslocation, net photosynthesis and morphological development in interior spruce seedlings

One-year-old interior spruce (Picea glauca (Moench) Voss × Picea engelmannii Parry) spring-stock and summer-stock were grown under two phosphorus (P) fertility regimes, with (+P) or without (−P), followed by a simulated winter, and a second growing period under an adequate fertility regime in a controlled environment room. The two stock-types differed in their response to low P availability. For spring-stock, morphological development, phosphorus-use efficiency (PUE) and P specific absorption rate (SAR) were similar between −P and +P seedlings. For summer-stock, −P seedlings compared to +P seedlings had lower (p ≤ 0.05) morphological development, but greater PUE and SAR. For both stock-types, P content increased in +P seedlings, remained low in −P seedlings, and P concentration decreased in nursery-needles (i.e., formed in the nursery) of −P seedlings. The difference in stock-type response to low phosphorus availability (−P) was attributed to internal supply of P and its retranslocation. Assimilation (A) of CO2 in nursery-needles was similar between −P and +P seedlings for both stock-types. For spring-stock, +P seedlings had greater A in new-needles (i.e., needles formed during the trial) than −P seedlings. It was recommended that the spring-stock be selected over summer-stock for sites low in P availability.

Influence of nursery culture on western red cedar

Western red cedar (Thuja plicata Donn) seedlings were grown in a greenhouse and subjected to six nursery cultural treatments (long-day wet (LDW), long-day moderate (LDM), long-day dry (LDD), short-day wet (SDW), short-day moderate (SDM), and short-day dry (SDD)) during mid-summer. Seedling attributes were measured before fall and spring planting.Short-day and moisture stress treatments reduced shoot but not root growth, resulting in reduced shoot to root ratios. Fall tested LDW seedlings had a higher osmotic potential at saturation and turgor loss point than other treatments. Fall tested short-day seedlings had lower resistance to plant water movement. The LDW seedlings had the greatest new root growth in fall testing, while one of the lowest in spring testing. In the fall, LDW seedlings had the greatest net photosynthesis (Pn) at 25 °C root temperature, with all treatments having a similar decline in Pn as root temperatures decreased to 1 °C. In the spring, all treatments had a similar decline in Pn with decreasing predawn shoot water potential. Moisture stress and short-day nursery cultural treatments applied in mid-summer will not harden western red cedar seedlings for all potential field conditions.Spring, compared to fall, tested seedlings had two times the shoot and three times the root dry weight. Spring tested seedlings had a lower osmotic potential, maximum modulus of elasticity, relative water content at turgor loss point and greater dry weight fraction. Fall, compared to spring, tested seedlings had lower resistance to plant water movement and greater cuticular transpiration. In general, fall tested seedlings had more root growth than spring tested seedlings. Spring, compared to fall, tested seedlings generally had greater stress resistance.

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.