Rising air humidity during spring does not trigger leaf-out in temperate woody plants

• Published in: The New phytologist Vol. 225; no. 1; pp. 16 - 20
• Main Authors: Zohner, Constantin M., Strauß, Aurelia F. T., Baumgarten, Frederik, Vitasse, Yann, Renner, Susanne S.
• Format: Journal Article
• Language: English
• Published: England Wiley 01.01.2020; Wiley Subscription Services, Inc
• Subjects: Air; air humidity; Air temperature; Biogeochemical cycle; Biogeochemical cycles; Biogeochemistry; Climate Change; Humidity; leaf‐out; Leaves; Letters; phenology; Photoperiods; Plant Leaves - physiology; Seasons; Species; Spring; Spring (season); temperate trees; Temperature; Trees - physiology; Woody plants; air humidity; temperature; leaf-out; temperate trees; phenology; climate change
• ISSN: 0028-646X; 1469-8137
• DOI: 10.1111/nph.16182

The timing of spring leaf emergence in temperate regions directly influences global biogeochemical cycles and species interactions (Richardson et al., 2013). Understanding the environmental drivers of leaf‐out is thus essential to forecasting ecosystem responses to global climate change. These drivers have long been thought to be species‐specific combinations of spring temperature, winter chilling, and increasing day length during spring. Temperature‐related increases in air humidity were suggested as an alternative trigger of the spring bud break recently, based on experimental results from nine Eurasian and American tree species, including two needle‐leaved trees. The new hypothesis was cast into doubt, however, by experiments on 15 further species, again from both Eurasia and America, with one, Cornus mas, being used in both studies (Zipf & Primack, 2017). These contradictory conclusions raise basic questions about (1) the type of experiments in use for studying environmental leaf‐out triggers, and (2) the extent of species differences in leaf‐out triggers, and hence the influence of the identity of species studied on the results.