, 2013a). Moreover, in genotype Koster we observed a high increment of Cr in the second rotation, as compared to Skado. This could be because Skado grew faster than Koster in the first rotation, and occupied the soil more rapidly. In the second rotation Skado had less space to grow, while Koster still had some soil to occupy. The potential of SRWC to sequester C in the soil has

been recently questioned by Walter et al. (2014). However, the belowground woody biomass (Stu + Cr + Mr) represents the second largest C pool of the SRWC system (Berhongaray, 2014). This long-term belowground biomass also contributed to the enhancement of the C sequestration AZD5363 along the four years of the plantation (Pacaldo et al., 2014). The value observed for the C sequestration (240 g C m−2) was much higher than the 90 g C m−2 reported for an SRWC plantation in Canada (Arevalo et al., 2011). This might be due to the higher planting density at our site. Although the aboveground biomass for genotype Skado was 23% higher than for Koster, there were no differences in the total belowground biomass. Another study that compared aboveground contrasting genotypes also found that genotypes were less clearly contrasted belowground than aboveground (Dickmann et al., 1996). The root:shoot ratio exponentially decreased with basal area in a similar way for

both genotypes before and after coppice (pre- and post-coppice, Fig. 6). This interesting mTOR inhibitor observation rejected our second hypothesis of a change in the root:shoot ratio after a tree is converted from a single-stem to a multi-shoot system (i.e. from pre- to post-coppice). As for the Cr biomass the genotypic differences in root:shoot else ratios were attributed to differences in the BA. For young Scots pines an increment of the root:shoot ratio with stem diameter increment was reported, in contrast to our findings (Xiao and Ceulemans, 2004). This could be explained by the fact that these evergreen

trees were growing on poor forest soils. Similar to various other studies (reviewed by Mokany et al., 2006) we found that the root:shoot ratio increased with increasing aboveground biomass. Biomass allocation (to above- versus belowground) was not under strong genetic control, in contrast to some other studies that compared different poplar genotypes (King et al., 1999 and Yin et al., 2005). In this study we compared, however, only two genotypes under non-limiting growth conditions. In this study we used the technique of core sampling for the determination of Fr biomass, and tree excavation for the biomass estimations of Mr and Cr. The core sampling methodology is recommended for the sampling of uniformly distributed roots, such as for Fr biomass (Levillain et al., 2011). With increasing root diameters the (spatial) variability of the lateral root distribution also increases; so the sampling of an increasing amount of soil volume enables a better sampling of this belowground heterogeneity.