Root xylem CO2 flux: an important but unaccounted-for component of root respiration

Elevated CO2 does not affect stem CO2 efflux nor stem respiration in a dry Eucalyptus woodland, but it shifts the vertical gradient in xylem [CO2]

“…During this time, xylem [CO 2 ] measured at 0.5‐m stem height was higher in eCO 2 rings, whereas there were no differences at 1 m height. Given that a substantial part of root respired CO 2 remains within the root system and is transported aboveground through the xylem, xylem [CO 2 ] could be used as an indirect indicator of the root respiratory activity (reviewed by Bloemen, Teskey, McGuire, Aubrey, & Steppe, ). In a P .…”

Modelling the diurnal and seasonal dynamics of soil CO<sub>2</sub> exchange in a semiarid ecosystem with high plant–interspace heterogeneity

“…Our simulations showed that a considerable fraction of CO 2 produced could be removed by root uptake and leave the volume measured by the respiration chamber. Bloemen et al (2016) showed that the CO 2 concentration in root xylems could be higher than in soil solutions. This implies that such a "missing source" might be even greater than the model estimation, although knowledge is still limited about the efficiency of the removal and the diffusion/release of CO 2 during the transport (Bloemen et al, 2016).…”

“…Bloemen et al (2016) showed that the CO 2 concentration in root xylems could be higher than in soil solutions. This implies that such a "missing source" might be even greater than the model estimation, although knowledge is still limited about the efficiency of the removal and the diffusion/release of CO 2 during the transport (Bloemen et al, 2016). The contributions of biocrusts as C sinks or sources have remained largely unknown (Castillo-Monroy et al, 2011).…”

“…Gas-transport processes are im-portant mechanisms regulating the magnitudes and hysteretic features of soil CO 2 fluxes (Ma et al, 2013). A substantial fraction of respired CO 2 may be transported to the atmosphere via xylem and may not be measured by techniques like soil reparation chambers (Bloemen et al, 2013(Bloemen et al, , 2016. During wet periods, soil CO 2 efflux could decrease significantly by water clogging of soil pores, which restricts the diffusion of O 2 and CO 2 gases (Šimunek and Suarez, 1993;Fang and Moncrieff, 1999).…”

Editorial note for the special issue “Dynamics and physiological processes of tree roots”

“…Although a number of papers were published on root dynamics related to below-ground carbon flux in the past decades as mentioned above, there are still many uncertainties. Bloemen et al (2016), in their review, showed that a substantial proportion of CO 2 derived from root respiration remained in root systems and was transported through the transpiration stream. Although these findings were obtained from a limited number of species so far, this phenomenon could impact our current understanding of carbon dynamics in terrestrial ecosystems or CO 2 metabolism in trees.…”