Effectiveness of freezer storage in fulfilling the chilling requirement of fall-lifted ponderosa pine seedlings

Abstract

Application.To ensure that freezer storage will satisfy chilling requirements in fall-lifted ponderosa pine, seedlings should be harvested late in the fall. Lifting seedlings too early in the fall may result in poor shoot development after planting and may delay budbreak even into the second year.Abstract. The degree to which freezer storage fulfilled the chilling requirement of ponderosa pine (Pinus ponderosa Dougl. ex Laws.) seedlings of two sources was determined by monitoring their development after potting or planting. The seedlings were lifted in September, October, November, or March and subjected to storage before outplanting. The fulfillment of chilling was assessed by measuring days to budbreak, cumulative percentage of seedlings flushing, foliated shoot length, and rate of bud abortion. The effect of freezer storage depended on stage of seedling development at lifting, length of storage, and seed source. Storage did not totally replace winter conditions, especially for seedlings lifted in September and October. Those from a high-elevation seed source flushed sooner than those from a low-elevation source. Delayed budbreak after planting of early lifted seedlings from the high-elevation source disappeared in the second year, but those from the low-elevation source continued to show effects. Seedlings lifted and stored in November had patterns of budbreak that were similar to those of seedlings that had overwintered in beds.

Tradeoffs between chilling and forcing in satisfying dormancy requirements for Pacific Northwest tree species

“…Although the information is based on only a few genotypes, the pine genotypes evaluated had similar observed responses. However, due to differences in the responses among pine species at low chilling and reported differences in responses to chilling or lack of chilling previously reported for ponderosa pine (Burr et al, 1989 ; Omi et al, 1991 ; Sloan, 1991 ; Wenny et al, 2002 ) we plan to follow up with trials involving more genotypes per pine species. Douglas-fir (Gould et al, 2011 ) and Pacific madrone (this study) both exhibited substantial differences in the possibility lines for genotypes within each species, indicating substantial genetic variation may exist in chilling and forcing requirements for budburst.…”

Overestimation of the effect of climatic warming on spring phenology due to misrepresentation of chilling

“…Another commonly used upper-temperature threshold for chilling is 5 °C 11 , 18 . Some studies, however, have suggested that subfreezing temperatures were effective 36 , 37 , so we also tested chilling models using −10 °C as the lower limit. Many studies have also assumed that freezing temperatures did not contribute to winter CA and only included temperatures >0 °C for calculating CA 11 , 38 .…”