Willow clones

Research on poplar tree clones for bioenetgy by Oak Ridge National Laboratory and its affiliated Universities, by the US Forest Service-North Central Forest Experiment Station, and by members of U.S. Poplar Council is extensive. As a result of this research, an EPS affiliated nursery is currently growing 8 ha of NM-6 hybrid poplar stool trees. Other commercial nurseries are also growing hybrid poplar and willow clones for cuttings. 

Fig. 1 TGA thermogram of biomass from reference willow clone S. dasyclados SVl. Arrow indicates cutoff line for water loss correction (129 °C). Block A weight loss representative of hemicellulose (245-290 °C). Block B weight loss representative of cellulose (290-350 °C). Block C weight loss representative of lignin (350-525 C)...

No discrete groupings or clusters were observed among the clones when plotted in a 3D graph (Fig. 2). Several multivariate analyses were performed, but all proved to be inconclusive and are not presented here. Most of the willow clones analyzed have similar biomass composition however, there are several clones that have distinctively more or less cellulose, hemicellulose, or lignin (Fig. 2). This could be very important in future selection of willow varieties optimized for a particular application. 

WILLOW CLONES VARY IN THEIR PROPERTIES TO TAKE UP METALS... 

Owing to the variation in these properties, one can find willow clones with a combination of properties suited to specific situations, for example to work as phytoextractors of Cd (Greger and Landberg, 1999). 

EXUDATES FROM ROOTS OF WILLOW CLONES WITH DIFFERENT METAL UPTAKE PROPERTIES... 

Variations in the composition of root exudates may be one cause of difference in metal uptake between plant species and genotypes (Mench and Martin, 1991). It is important to investigate if the differences in accumulation capacities for metals by willow clones can be related to differences in rhizosphere processes. It is necessary to ask, therefore, how soil chemistry is influenced by the presence of willow roots, if soil chemistry varies between willow clones with properties of low and high metal accumulation and if the mechanisms are metal - or concentration - specific. 

The conclusion one can draw from this work is that rhizosphere mechanisms involved in the release of metals from soil colloids may differ between metals as well as between willow clones with different properties of metal accumulation. Most of these mechanisms are found in low accumulators. Mechanisms involving pH seem to be important for both Cd and Cu accumulation. High pH decreases Cd release in soil with low Cd content and an increase in pH decreases the release of Cu from soil with high Cu level by low-Cu-accumulating clones. 

In the case of Zn, organic acids and/or peptides seem to be important in reducing Zn uptake in soil with a low Zn content, while increasing pH function as a mechanism to decrease Zn uptake in soil with a high Zn content. Thus, rhi-zosphere processes may partly account for the differences in the ability of willow clones to accumulate Cd, Zn and Cu. 

Leaf surface compounds provide important information about host-plant acceptability to coleopteran insects. Although the tortoise beetle, Cassida canaliculata, is only weakly attracted to odors from host plants, it shows strong preferences for host plants when additional contact cues are provided.64 The cottonwood leaf beetle, Chrysomela scripta, which is a pest of cottonwood, poplar, and willow, is stimulated to feed by leaf surface chemicals produced by a beetle-preferred poplar clone 65 The feeding stimulants have been isolated and identified as 1-docosanol, 1-tetracosanol, 1-hexacosanol, 1-octacosanol, 1-triacontanol, and... 

Influence of willow (Salix viminalis L.) roots on soil metal chemistry Effects of clones with varying metal uptake potential... 

Landberg, T., Greger, M., 1994. Can heavy metal tolerant clones of Salix be used as vegetation filters on heavy metal contaminated land In Perttu, K., Aronsson, P. (Eds.), Willow Vegetation Filters for Municipal Wastewaters and Sludges, Rapport 50, Swedish University of Agricultural Sciences, Uppsala, pp. 133-144. 

Labrecque M, Teodorescu TI. 2005. Field Performance and Biomass Production of 12 Willow and Poplar Clones in Short-Rotation Coppice in Southern Quebec (Canada). Biomass Bioener. 29 1-9. 

Sweden currently derives about 9% of its total energy requirements from biomass. They have a very interesting series of advanced biomass trials with fast-growing willows. They now have nine clones which have twice the yield (about 15 dry tonnes/ha/yr) of those previously used. If so desired the Swedes could derive half their energy requirements from biomass. 

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