Xylem cell length under drought and its value for predicting radial growth of SRF poplar cultivars (Populus spp.)

Abstract

Xylem cell length of juvenile tree rings was investigated in poplars in order to check the hypotheses that fiber length or vessel element length are indicative of drought tolerance and have predictive value for final stem base diameter at the end of rotation. The radial increment in the drought year 2003 served as the reference indicator for quantifying drought tolerance. All nine investigated cultivars suffered severely. In terms of their moderately decreased radial increment in 2003, the two aspen cultivars were clearly less drought susceptible than the seven hybrid poplar cultivars. The variance components of xylem cell length data explained by the two genetic factors ‘cultivar’ and ‘botanic section’ as well as the ‘tree ring’ (of the years 2002 and 2003) were compared by means of ANOVAs. The cultivar effects were superior to the effects of the critical precipitation status in 2003 and the botanic section. Fiber and vessel element length were found to be less sensitive to the drought compared with radial increment. They did neither correlate with radial increment in the drought year 2003 nor in 2002. Therefore, higher xylem cell length cannot indicate drought tolerance in poplars. However, a linear relationship between fiber length of both juvenile tree rings and the stem base diameter proved to be highly significant to a linear mixed effect model. Higher fiber length of a juvenile tree ring was considered to be predictive of larger stem base diameter at the end of rotation.