Synchronous and asynchronous root and shoot phenology in temperate woody seedlings

Understanding variation in root and shoot growth phenology among species is crucial to understanding underlying mechanisms of temporal niche differentiation. However, little is known about the relationship between root and shoot phenology, or how this relationship varies among functional traits. We examined fine root and shoot phenology of 42 seedlings representing a variety of woody species that inhabit the cool temperate forests of northern Japan. Some aspects of phenology were common to the pool of species examined: we found positive relationships between root and shoot phenology for the end of growth, and for the duration of growth, but not for the start of growth. Further, seedlings that started root growth relatively early also ended root growth relatively late. Other aspects of phenology varied predictably with functional traits, i.e. leaf habit and successional status: first, root growth in evergreen species started significantly earlier and ended later than in deciduous species; second, early successional species had the longest duration of shoot growth among all successional types. Our results suggest that niche differentiation may be promoted by differences in phenology between root and shoots, likely contributing to the co-existence of woody seedlings in temperate forests.

Methods
The relative growth rate was measured every 1-2 weeks over one yea in Hokkaido, Japan. The root growth was measured by using rhizobox.