Phenological patterns and factors affecting the lifespan of fine roots in forests

The phenology and lifespan of fine roots influence plant resource acquisition and fine-root carbon fluxes into soil, yet the extent to which fine-root phenology and lifespan vary across species and plant functional types, as well as the underlying drivers of this variation, remain poorly understood. We observed fine-root lifespan, production and mortality dynamics in 11 temperate forest species for two consecutive years using minirhizotrons, and measured leaf lifespan (LL). We tested the influence of environmental factors on fine-root dynamics and determined whether traits affecting lifespan differed among leaves and roots. Peak fine-root production mainly occurred in early summer followed by the peak of fine-root mortality, occurring mainly in late summer. The median fine-root lifespan (MRL) was negatively and positively associated with root nitrogen concentration and root diameter, respectively. In contrast, the best predictors of LL were leaf tissue density and specific leaf area. The MRL and LL were not related. Our results highlight that, although leaves and fine roots were partly influenced by the same trade-off between high metabolism and long lifespan, MRL is largely noncoordinated with LL, suggesting temporally decoupled ecological strategies above and belowground for maintaining functional resource-acquisition organs. Furthermore, species-specific patterns of root production suggest variable strategies among species to enhance resource acquisition. Such differences also imply variable influences of species on carbon dynamics in temperate forests.