Genetic studies on wood properties, growth and disease in Populus have been substantial, but genetic investigations of stem hydraulic properties of Populus are currently lacking. Three main hypotheses were tested: (1) Tyree’s hypothesis (2003) that high hydraulic conductivity is a prerequisite for fast plant growth; (2) growth and stem hydraulic properties, such as hydraulic conductivity, and mean vessel diameter, are heritable and genetically correlated; and (3) genotypic variation in stem hydraulic properties result in different growth strategies. We studied 24 genotypes (including the parents) of a pseudo backcross population of Populus deltoides and Populus trichocarpa x deltoides. Seedlings were grown for three months from vegetative cuttings in controlled greenhouse conditions, with adequate light, water, and nitrogen. We quantified variation in stem hydraulic properties, foliar carbon isotopes and growth. Significant differences between the parental genotypes were found for most traits examined, while the progeny displayed a wide range of phenotypes extending beyond the parental means. Moderate broad-sense heritabilities were found for growth traits, hydraulic conductivity and xylem anatomy. Genotypes with higher hydraulic conductivity displayed higher relative diameter growth rate, and these traits were genetically correlated. Carbon isotope discrimination, vessel number per sapwood area, and hydraulically weighted vessel diameter were also genetically correlated with relative diameter growth rate. Preliminary results indicate that a tradeoff between larger vessels and vessel density may exist and result in different strategies to achieve similar growth rates.

References:

Tyree, M.T. 2003. Hydraulic limits on tree performance: transpiration, carbon gain and growth of trees. Trees. 17:95-100.