Experimental dataset for the effect of chilling on budburst

Description

Notes

Methods

To identify phenological experiments that manipulated chilling and forcing, we searched both ISI Web of Science and Google Scholar with TOPIC = (budburst OR leaf out OR flowering OR phenology) AND chilling. The initial searches yielded more than 200 papers. Subsequently, we reviewed and assessed each paper strictly. The papers that were included in the analyses needed to meet the following criteria: (1) focusing on plant species existing in the ground phenological dataset; (2) testing for the effects of chilling on budburst, leaf-out or flowering; (3) having at least 3 chilling treatments. As a result, only 23 papers were included in the analyses.

These papers first exposed dormant twigs or seedlings to different periods of natural low temperatures in the field or artificial low temperatures in the refrigerator and then to different forcing temperature and photoperiod regimes in growth chambers. The most important response data in these papers are days to budburst and duration of chilling treatments (i.e., starting and ending date of chilling treatments). We used GetData Graph Digitizer (http://www.getdata-graph-digitizer.com/index.php) to scrape these response data from the figures of each paper or directly extract the data from the tables of each paper whenever possible. For studies simultaneously testing the effects of photoperiod on budburst timing, we only retained the results under long photoperiod treatment (removing the data under short photoperiod), so as to mirror the photoperiod in natural conditions. Many papers reported the degree days to budburst rather than the days to budburst. In these cases, we converted the degree days to budburst to days to budburst according to the forcing treatments in the experiments and algorithms of degree-day (i.e., starting date and temperature threshold). Meanwhile, we added relevant information to the response data according to the contents of each paper, including the sampling site of plant materials, sampling year and date, provenance origin of plant materials, chilling temperature (natural chilling or experimental chilling), forcing temperature, and forcing photoperiod.

Following the above processes, we constructed an experimental dataset involving 50 temperate woody species. Because different provenances of the same species may vary in their phenological response to chilling (Alberto, et al., 2013; Guo, et al., 2020; Thibault, et al., 2020), we compared the experimental data with the observation data at the provenance level. As a result, 94 species/provenances (64 in Europe and 30 in North America) were analyzed  For each species/provenance in the experimental data, we determined the leaf morphology (coniferous or broadleaved species), plant material (twig or seedling), types of chilling treatment (natural chilling or artificial chilling), types of forcing treatment (different day/night temperature or constant temperature).