Effects of root diameter, branch order, soil depth and season of birth on fine root life span in five temperate tree species

Abstract

Fine root life span is a key variable influencing the belowground dynamics of forest ecosystems and is known to be associated with a complex suite of endogenous and environmental factors. We investigated how root life span is influenced by root diameter, branch order, season of birth and soil depth of birth for five temperate tree species growing in monoculture plantations at a common site in northeastern China. The minirhizotron approach was used to estimate root life span from April 2008 to October 2009. Cox proportional hazards regression analysis was employed to determine the impact of those four factors on root life span of each species. There was no consistent difference in fine root life span between evergreen conifers and deciduous hardwoods. A bimodal frequency distribution of root life span was observed for all the species; the majority of roots born in summer and autumn survived to the following year, while roots born in spring mostly died in the current growing season. Root life span tended to increase with root diameter across all species, except Juglans mandshurica. The first two root branch orders within each species generally shared similar life span, with the exception of Picea koraiensis. Root life span tended to be longer at greater depths in the soil profile across all five species. Our results suggest that root life span generally depends on complex interrelations among root anatomy, soil environment and seasonal climatic conditions.