Effects of drought and nutrients on growth, morphology and wood anatomy of two genotypes of Salix

Abstract: Due to a growing global population and an increasing welfare in combination with limited resources of fossil fuels and environmental problems may bioenergy be one of the alternatives for a more sustainable energy production. Among others, Salix is used as biological energy source. Its energy conversion is high compared to other sources and it can be managed in a short rotation period. For future energy production of Salix it is important to have resource efficient genotypes with high biomass production. Thus, to secure future production, it is im-portant to breed for production and resource use efficiency traits. Objectives with this study were to evaluate how water and nutrients affect biomass production of two genotypes of Salix and how xylem diameter of the same genotypes is affected by drought stress. Main hypothe-ses with this study are that drought stressed plants have slower and lower biomass production than well-watered plants. That available nitrogen (N) increase growth, that genotype 341 has a drought tolerance than genotype 223 and that xylem vessels are narrower for drought stressed plants compared to well-watered plants. Salix cuttings of the genotypes 223 and 341 from a mapping population of Salix viminalis and the hybrid S. vinimalis x S. schwerinii were planted and grown in a greenhouse in Uppsala, central Sweden, with a three week long treatment pe-riod before final harvest. Greenhouse trial includes four treatments (control) 250 ml water three times a week; water and nutrients) 250 ml water three times a week and 2 ml “Blomstra” fertilizer/ l water once a week; nutrients) 250 ml water with 2 ml “Blomstra” fertilizer/ l water once a week; water shortage treatment) 250 ml water once a week). Additionally, stems of plants grown in a field trial in northern Italy for three years were collected. The stems were irradiated with X-ray emanation for creation of a 3D-picture of the stem, the cross-section of the pictures were used for counting vessels and analyzing vessel size. Both treatment and genotype affected plant growth. Genotype 341 was more affected by the treatments than genotype 223 but genotype 223 had an overall lower production. The production of the geno-types differed mainly within treatment of high water and nutrient availability and the drought treatment. The results indicate a more resource efficient production of the genotype 341 in relation to water and nutrients and also a greater drought tolerance compared to genotype 223. Highest nitrogen content was observed in fertilized plants, however in contrast to other stud-ies soil water supply did not significantly affect N concentration in leaves. Greater vessel area was observed in irrigated plants. Stem diameter was positively correlated with both total ves-sel area and amounts of vessels. Amounts of vessels also tended to be negatively correlated to δ13C and to standardized WUE (water use efficiency based on δ13C in relation to stem diame-ter). For future studies a longer treatment period is recommended as well as increased number of replicates for xylem analysis. I conclude that genotype 341 has great potential for biomass production, is better suited for biomass production than genotype 223 and therefore recom-mended to use in future trials.