| Dedicated plantations of woody species (short rotation woody crops, SRWC) are being developed as a sustainable land use option that provides a host of environmental and social benefits, while serving society's needs for a renewable feedstock that can be converted into energy and/or bioproducts. Willows (Salix spp.) have shown a lot of promise in SRWC applications in the northeastern United States and Western Europe. A continuing major barrier to the greater deployment of SRWC willow is its high feedstock production cost, relative to feedstock derived from fossil sources. Improving the productivity of the system through the development and deployment of improved high-yielding planting material will lead to a lowering of the cost of feedstock production. This study comprises three experiments conducted to examine the production ecology of willow in an effort to inform crop development research. The experiments studied trait associations in relation to biomass production, light use efficiency of clones, and the interactive effects of water and nitrogen supply on wholeplant and leaf-level responses.; The first study assessed morphological variation in 11 select traits in 30 willow clones at the end of a 3-year rotation and found that (1) substantial clonal and inter-specific variation exists in all traits studied, thereby allowing selection efforts to focus on clones with desirable traits, and (2) high biomass producers adopted alternative strategies in terms of their investment in canopy structure and foliage apparatus.; The second study examined light interception and conversion in relation to biomass production in five clones in a post coppice context. Variation in clonal productivity was related both to the amount of light intercepted and the efficiency with which that light converted to dry matter (LUE). High leaf-level photosynthetic rates combined with foliage morphological characteristics that are conducive to maximum carbon gain ii high-light conditions were more important for maximizing LUE, rather than "optimization" of intra-canopy light distribution and photosynthesis.; The third study was a multifactorial experiment conducted in a greenhouse that explored the interactive effects of nitrogen and water availability in four willow clones. Treatment effects on growth, allocational and physiological processes were found to be interactive rather than additive. Clones responded differently not only to changes in the availability of single resources, but also to specific combinations of resource levels. Allocation and growth-related plasticity was greater and presumably had greater adaptive value than leaf-level plasticity. The diverse clonal adaptation strategies expressed through traits such as leaf area deployment, root-shoot ratios, photosynthetic rates and water use efficiency (WUE), have implications for the use of these clones on different sites and for different applications. None of the clones in the study was superior in terms of stem biomass production across all treatments, underscoring the importance of evaluating clonal performance under multifactorial environments. |
