Winter frost damage and its link to early growth and survival in a poplar clone collection

The Northern European countries largely rely on poplars and their hybrids that are transferred northward from more southern regions, therefore, facing a trade-off between the use of full growth potential and sufficient tolerance of low temperatures. We characterized frost damage and its link to early growth and survival of 33 poplar genotypes at the age of one, three, and four years in a clonal collection on agricultural land. The survival after the first season varied from 42% to 99%. Half of the clones had autumn frost injuries with a maximum of 20% of trees damaged. The autumn frost-damaged trees were significantly (p < 0.001) higher before the injury than the undamaged trees with site mean 105.3 ± 7.9 and 72.0 ± 2.5 cm, respectively, but, at the clone mean level, the proportion of autumn frost-damaged trees had no link to survival (rho = 0.53, p < 0.001). The observed winter frost damage showed no relation (p < 0.05) regarding the proportion of trees with autumn frost damage. Trees with winter frost damage tended to be shorter than undamaged trees (p < 0.001) and had lower survival (rho = 0.47, p < 0.01). The maximum height difference of the clones among the studied years was in a magnitude from 2.4 to 2.9, and the stability of a clonal ranking increased with the age. The results emphasize the need for further monitoring of the clone performance under the local climatic conditions before recommendations of commercial use of particular clones in Latvia.

Will tree species experience increased frost damage due to climate change because of changes in leaf phenology?

In temperate zones, trees tend to unfold their leaves earlier due to climate warming. However, changes in the timing of the bud development also affect the dynamics of the cold-hardening process, which may increase frost injuries endured by trees because new leaves unfold at a period when frost events can still occur. This possible increase in frost damage in response to climate change is known as the “frost-damage hypothesis”. In this study, we have tested this hypothesis by forcing a process-based frost-injury model with process-based phenological models for 22 North American species with two Intergovernmental Panel on Climate Change storylines. Using a simplified parameterization of the frost-injury model, we found that risk of frost injury changed with climate change for all species. In fact, frost injury decreased for the vast majority of the species, but this trend varied across species and throughout each species’ distribution. We further explored the variability of response among species using their phenological and geographic characteristics. The interspecific trends depicted here show what could be the implications of climate change on the ecophysiology of boreal and temperate trees and highlight the importance of process-based models in studying the complexity of long-term impacts of climate change on species biology.

Frost Dehardening and Rehardening of Hydrangea macrophylla Stems and Buds

Hydrangea macrophylla is a popular and commercially important flowering shrub, but frost injury of buds and current-year shoots is a common problem in some of its cultivars. As a result of climate warming, temperate winters are becoming progressively milder, and temperature patterns are becoming increasingly irregular with an increased frequency of warm spells. Warm spells may induce premature dehardening, increasing the risk of subsequent freezing injuries. This study investigated cold-hardiness of stems and buds of Hydrangea macrophylla ssp. macrophylla (Thunb.) Ser. ‘Alma’ during dehardening in response to simulated warm spells and subsequent rehardening in January and early March. Plants were acclimated in the field and dehardened in the greenhouse at controlled warm temperatures for various durations. Dehardened plants were rehardened for up to 12 days in an unheated greenhouse (January) or in the field (March). Buds of H. macrophylla were slightly less cold-hardy than stems. In both stems and buds, the dehardening resistance and the rate of dehardening were influenced by temperature, but buds appeared to be less resistant to dehardening and dehardened faster than stems. In stems, dehardening proceeded faster in March than in January, and the capacity of the stems to reharden seemed reduced, indicating that both dehardening and rehardening were influenced by the progression of winter. Results of this study indicate that buds of H. macrophylla are more sensitive to frost injury than stems and the vulnerability of stems to frost injuries, caused by an unstable temperature regime, changes during the winter season.

Biochemical changes in pear (Pyrus communis L. depending on different phases of the dormancy

Pear cultivars of variable frost tolerance were tested as for frost injuries suffered as a consequence of artificial freezing temperatures during the endodormancy as well as the ecodormancy. Damages were registered according to a visually defined scale, then peroxidase and polyphenol-oxidase activity was checked in buds, spurs and limbs. According to our results, 'Packham's Triumph' was the most frost tolerant cultivar. Regarding enzyme activity of both enzymes, the performance of cultivars displaying different susceptibility was also different in spurs as well as in buds. Results referring to the endodormancy were especially instructive. During the ecodormancy, data obtained at the same time indicated the differences existing between the developmental stages of dormancy in the respective cultivars.

Biochemical changes in pear (Pyrus communis L. depending on different phases of the dormancy

Pear cultivars of variable frost tolerance were tested as for frost injuries suffered as a consequence of artificial freezing temperatures during the endodormancy as well as the ecodormancy. Damages were registered according to a visually defined scale, then peroxidase and polyphenol-oxidase activity was checked in buds, spurs and limbs. According to our results, 'Packham's Triumph' was the most frost tolerant cultivar. Regarding enzyme activity of both enzymes, the performance of cultivars displaying different susceptibility was also different in spurs as well as in buds. Results referring to the endodormancy were especially instructive. During the ecodormancy, data obtained at the same time indicated the differences existing between the developmental stages of dormancy in the respective cultivars.