Temperature sensitivity of root respiration declines with increasing soil depth in six temperate tree species

Aims Root respiration and its temperature sensitivity ( Q 10 ) are key parameters for understanding the processes and mechanisms of carbon cycling in forest ecosystems. However, the variation and influencing factors of root respiration rate and Q 10 among soil depths have been poorly explored. Methods We measured root respiration rates of the first five orders at 6, 18 and 24 °C, in surface (0–10 cm) and subsurface (20–30 cm) soil layers in six temperate tree species ( Fraxinus mandshurica , Phellodendron amurense , Prunus padus , Larix gmelinii , Picea koraiensis and Pinus sylvestris var. mongolica ) and calculated their Q 10 . Concurrently, we determined root morphological and chemical traits and soil properties. Results Shallow roots generally exhibited faster respiration rates and higher Q 10 , which was more prominent in the first two order roots. Respiration rates of the first two orders measured at 18 °C were positively correlated with root diameter, root nitrogen concentration and ambient soil temperature (significant only for the first order), but negatively with root tissue density. By contrast, Q 10 values were only significantly correlated with soil temperature on the day of root sampling. Furthermore, according to the conceptual framework of the root economics space, root traits along the “conservation” gradient were mainly affected by soil depth, with shallow roots showing “fast” respiration rates and high nitrogen concentrations. Conclusions The systematic variation of root respiration and Q 10 between soil depths and among root orders should be considered towards a mechanistic understanding of carbon cycling in forest ecosystems which would shed light on modeling the carbon cycle.