Minimum spring temperatures at the provenance origin drive leaf phenology in sugar maple populations

Late frost can cause damage to trees, especially to the developing bud of broadleaf species in spring. Through long-term adaptation, plants adjust leaf phenology to achieve an optimal trade-off between growing season length and frost avoidance. In this study, we aim to assess ecotypic differentiation in leaf development of sugar maple populations planted in a common garden. A total of 272 sugar maple seedlings from 29 Canadian provenances were planted at the northern boundary of the natural range, and the phenological phases of bud and leaf development were monitored during spring 2019. The wide geographical area under evaluation showed a complex seasonal pattern of temperature, with spring warming occurring later in the north and close to the sea. Overall, leaf development lasted between 20 and 36 days, from the end of May to end of June. We observed different timings and rates of leaf development among provenances, demonstrating the occurrence of ecotypes in this species. Minimum April temperatures of the original sites were able to explain such differences, while maximum April temperatures were not significant. Seedlings from sites with colder minimum April temperatures completed leaf development earlier and faster. On average, leaf development diverged by up to 6 days among provenances, with minimum April temperatures ranging from -3 to 3 °C. Our results demonstrated that the avoidance of late spring frost is a driving force of leaf development in sugar maple populations. In the colder sites, the growing season is a limiting factor for tree growth. Thus, when thermal conditions become favorable in spring, an earlier growth reactivation and high metabolic activity ensure a fast leaf emission, which maximizes the period available for photosynthesis and growth. These patterns demonstrate the long-term phenological adaptation of sugar maple populations to local climatic conditions and suggest the importance of frost events for leaf development.

Olive oil characterization of cv. 'Arauco' harvested at different times in areas with early frost in Mendoza, Argentina

BACKGROUND

'Arauco' is the only autochthonous olive cultivar from Argentina. Little has been reported so far regarding the management of this crop. In this work, variations in fruit and chemical characteristics of olives harvested over a wide range of dates and seasons are reported for this cultivar at two sites in Mendoza province in central west Argentina.

RESULTS

During the harvest periods studied, fruit oil content on a dry basis remained at its maximum and was stable, but fruit oil content on fresh basis increased as water content decreased with delay in harvest date. Harvest date affected the maturity index of fruits as well as the oxidative stability and phenolic content of oil. In contrast, the fatty acid profile was not consistently affected by harvest date. Environmental conditions, mainly the occurrence and intensity of frosts, strongly influenced oil quality as well as maturity with delay in harvest date.

CONCLUSION

The most appropriate harvest time to obtain Arauco oil with a high oil yield and good chemical quality was before mid-May and with maturity index lower than 2. Fruits harvested after mid-May were exposed to minimum temperatures between -1.2 °C and - 4.0 °C, producing oil with low phenolic compounds and oxidative stability. © 2019 Society of Chemical Industry.