Effect of Photoperiod, Night Temperature, and Frost Incidence on Development of Frost Hardiness in Pinus radiata

Abstract

The role of photoperiod, night temperature, and frequency and severity of frosts on the development of frost hardiness in seedlings of Pinus radiata was studied using controlled environment treatments. In one experiment the specific effects of 9 and 14 h photoperiods and 5 and 15°C night temperatures were examined. In a second experiment, seedlings were sequentially hardened under two simulated early autumn to late winter climates, with the photoperiod and day/night temperatures progressively altered at 11 and 21 day intervals respectively. In addition, half of the seedlings raised in each simulated climate were exposed concurrently to a conditioning frost regime. Frost hardiness of the seedlings in each sequence was determined at regular intervals using a series of evaluation frosts. Frosts of between -3 and -5°C were the most effective factor in controlling the development of frost hardiness. Night temperatures as low as 1°C were also effective but not those above 5°C. A minimum photoperiod requirement of less than 11 h for up to 42 days exposure was required for low-temperature hardening. There appeared to be a response lag in the development of frost hardiness once the critical photoperiod and inductive night temperatures had been imposed. Differences between nursery sites in frost hardiness of seedling stock were attributed to differences in their environments, particularly the incidence of frosts. The final maximum frost hardiness varied between the treatments from - 7.5 to -19°C indicating that Pinus radiata has a greater potential to develop frost hardiness than was previously thought from field observations.

Daylength, temperature and fertilization effects on desiccation resistance, cold hardiness and root growth potential of Picea mariana seedlings

“…Short day treated seedlings also became hardy to -10 °C sooner than NDW and NDWF seedlings, which could be attributed to a phenological advantage conferred by earlier growth cessation and bud initiation. More rapid hardening also occurred in OD compared to NDW and NDWF seedlings, and was likely due to the colder temperatures OD seedlings were exposed to outdoors [20]. It also may have been a response to desiccation [26], as desiccated tissues are more cold hardy than fully hydrated ones [28].…”

Seasonal frost tolerance of some ornamental, indigenous New Zealand plant species in the generaAstelia, Dicksonia, Leptospermum, Metrosideros, Phormium, Pittosporum, andSophora

“…The temperature was programmed to decline from a day temperature of 12±0.5°C to the minimum (frost) temperature over 6 h, to be held at the minimum selected temperature (± 0.5 0c) for 6 h, and to be returned again to 12°C over 4 h. In all instances the conditions maintained during the frost cycle were monitored and plant response data were recorded only from treatments which met these specifications. Other details of this 6 -6 -4 programme are described by Greer & Warrington (1982).…”

“…Furthermore, the good agreement between the results obtained using the controlled environment techniques and the classification of the same cultivars using hardiness zones, based on long-term observations over a range of field sites, indicates that both the techniques used and the hardiness induced by the Palmerston North environment provided realistic estimates of the seasonal frost hardiness patterns of the species studied. Plants introduced into New Zealand from other countries have been shown to retain the ability to acclimate to low temperatures if grown under appropriate inductive environments (Sakai et aI., 1981;Greer & Warrington 1982).…”

“…The temperature which induced visually detectable damage on at least 50070 of the individual plants in the sample (the frost hardiness temperature) and the temperature which caused death to at least 50% of the plants (the lethal temperature) were determined. Interpolation of results between two treatment temperatures was sometimes required (see Greer & Warrington 1982) to obtain closer estimates of either the frost hardiness temperature or the lethal temperature. Because of this interpolation, the precision of the estimates of the hardiness and the lethal temperatures was directly related to the differences between the temperatures used within each treatment series; i.e., to within ± 1 or ± 1.5°C.…”

Frost tolerance ofTrifoliumspecies

“…The temperature was reduced over 6 h from the day temperature of 12°C to the minimum temperature, was held at the minimum for 6 h, and then increased to 12°C over 4 h (Greer & Warrington 1982). Soil temperature was kept above 5°C by using a soil heating pad below the trays.…”