Phenotypic variability of tracheids in hybrid Larch breeding populations

Xylem cell characteristics are largely genetically determined. However, depending on site conditions, plant age and location within the tree, the expression of individual characteristics can vary over a wide range. The knowledge about specific wood characteristics is not only important for timber processing, but it is also a basis for the assessment of various physiological processes related to hydraulic architecture of a tree and thus, its capacity to adapt to environmental impacts.

A detailed analysis of different larch progenies on different sites and of specific annual rings provides information about the growth performance of the trees on an anatomical level and helps to explore the phenotypic variability of xylem cell size. Our research focuses on the characterization of tracheid size of 6 different hybrid larch (Larix x eurolepis A. Henry) progenies and one standard European larch (Larix decidua Mill.) (age 19 and 39 years) planted on different sites of Southeast Germany. Beside cell length within annual year rings (late and earlywood), cells of different cambial age and different height positions within the trunk (breast height and 6.5 m) were investigated. The span between longest and shortest cell within an individual genotype was calculated as a measure for the progeny-specific growth potential that can be expected regarding the individual study site. The aim of the study was to determine the progeny specific variability of cell size, to describe differences between late and earlywood and to explore differences between hybrid larch and European larch.

A negative correlation of the tracheid lengths with the trunk height above ground was found, which confirms the hypothesis of different authors that a significant decrease in cell size with increasing trunk height can be assumed. For each progeny and study site cell length increased with cambial age for both late and earlywood cells. Site specific differences of 3.6 % in a minimum and 13.6 % in a maximum between late and earlywood tracheids could be observed. A mayor finding is that tracheid lengths between individual sample trees of the same progeny at the same test site varies significantly which highlights the phenotypic plasticity of this morphological trait. Nevertheless, the comparison of sample trees of one progeny but different sites produced significant differences only for the young trial plots. The comparison of hybrid larch progenies with the European larch ‘Hasselburg’ couldn’t prove a superiority of hybrid larch.