Renewal bud traits as a link between whole plant traits and herbaceous species phenology

Abstract

Overwintering below-ground buds and organs determine spring regrowth of perennial herbs in temperate regions. This effect could also manifest further in the timing and duration of plant growth and flowering and has been documented in some species and organ types. However, to what extent this applies across the entire spectrum of below-ground organs, bud types and temperate herbs remains unclear. Here we measured the timing of spring growth and flowering pattern (first flowering day, day of peak growth, growth rate and flowering length) in a phylogenetically representative set of 243 species of temperate perennial herbs grown in semi-natural conditions of a botanical garden. These phenological traits were linked with data on bud traits (flower and leaf preformation, bud volume and bud scale coverage differentiation) as proximate drivers of species phenology and with whole plant traits (plant height, below-ground storage volume and bud bank traits) and analysed using non-phylogenetic and phylogenetic regression models and structural equation modelling. We showed that the timing of flowering and growth of perennial herbs was mainly determined by bud traits, namely flower and leaf preformation together with primordia volume. The often-reported link between smaller plant size and early flowering seems largely indirect and rather stemming from size constrains in flower-preforming species. Growth rate was predicted both directly by bud bank depth and indirectly through the association between storage volume and bud volume. Our study shows how the interplay between bud traits and whole plant traits determines herbaceous spring phenology. By identifying bud traits as the proximate drivers of spring phenology, we demonstrate that incorporating them into phenological studies will make possible more mechanistic understanding of how species phenology responds to external drivers such as temperature. This approach can enhance our understanding of species phenological shifts in response to global environmental changes. Read the free Plain Language Summary for this article on the Journal blog.