Clonal variation in nutrient content in woody biomass of hybrid aspen -: (Populus tremula L. x P-tremuloides Michx.)

Differences in the nutrient concentrations and nutrient amounts of stems and branches amongst clones of hybrid aspen (Populus tremula L. X P tremuloides Michx.) were investigated. Seven clones with superior and seven with medium growth rates were selected from a test of 119 clones in southern Sweden. Four trees per clone were randomly identified and harvested in dormant conditions. Sample discs from the stems and branches were collected and analysed for N, K, P, Ca, Mg, and S concentrations, as well as wood density. The analyses revealed significant genetic differences in wood density, K, P, and Mg concentrations in the stems. There were weak (non-significant) and negative genetic correlations between stem volume and concentrations of all the nutrients, except potassium, suggesting that nutrient-efficient clones could be selected without significantly sacrificing genetic gain for growth. In the branches K, Ca, and Mg concentrations differed significantly among clones. After selecting more nutrient efficient clones, the potential savings of nutrients compared with current hybrid aspen material was estimated to be around 5%, which seems fairly low, at least in a short-term perspective. However, the use of clones with different nutrient storage strategies may be regarded as a possible way in the long run to save nutrients in hybrid aspen ecosystems, or of removing them when sludge is applied.