Seasonal variation of leaf functional traits in sub‐Arctic plants

Leaf functional traits are informative of plant fitness and functions in ecosystems. These functional traits and their variation across geographic extents are much studied but less is known about their temporal variation over a growing season. Here, we provide an analysis of the seasonal variation in six leaf functional traits of 11 sub‐Arctic vascular plant species in northern Finland, highlighting significant temporal dynamics over a growing season. Our findings reveal that functional traits, including specific leaf area, leaf dry matter content, leaf area, leaf dry mass, brightness index, and greenness index, exhibit considerable variation across the 15‐week growing season. These temporal variations are influenced by plant growth forms, with distinct patterns observed among forbs, deciduous shrubs and evergreen shrubs. Our analyses show that the ranking of species based on traits is rather well preserved during the peak growing season in the most commonly used traits. Consequently, the timing of sampling has a rather minor impact on the relative trait differences across species as long as the sampling is not conducted in the very beginning and end of the growing season. However, if different species are measured at different times of the year, the seasonal effect can be notable. The growth forms often follow roughly similar temporal dynamics, and therefore, the error can be especially strong when comparing species across different growth forms.