SRC willow development, biomass composition and biofuel potential

Abstract

The aims of this PhD were to examine nitrogen allocation and partitioning in Short Rotation Coppice (SRC) willow in regard to tree development and to investigate biomass composition and cell wall structure for the purpose of assessing and understanding biofuel potential. To address these topics four major experiments were performed and are presented in the thesis. An investigation of SRC willow development and nitrogen dynamics was conducted as a pot trial comprising 14 different genotypes from a willow mapping population. The genotypes were selected on the extremity and consistency of their field biomass yields. Fertiliser enriched with the stable isotope nitrogen 15 was applied as a means of nitrogen surveillance. One of the findings was that higher biomass yielding varieties of SRC willow had increased nitrogen-use-efficiency yet less (or later) nitrogen remobilisation in the autumn. The recalcitrance of the cell wall to enzymatic saccharification was assessed across 138 field-grown genotypes of the same willow mapping population. The aim was to identify any relationships between glucose yield and several biomass yield traits and to identify any quantitative trait loci (QTL) associated with enzymatic saccharification. Four QTL associated to enzymatic saccharification were identified and no relationship was found between glucose and biomass yield traits. A third experiment aimed to modify cell wall composition and structure of a single cultivar of willow grown in a pot trial. Tension wood, fibre cells containing an extra cell wall layer unique to angiosperms, and cellulose synthesis inhibited phenotypes were both induced. These modifications were accomplished through chemical and environmental treatments during development and their impact on composition and cell wall recalcitrance was assessed. Tension wood formation was found to increase glucose yields. The final main experiment used 35 of the UK’s leading biomass yielding willow varieties, grown in the field, to assess not only the variation in composition and enzymatic saccharification but also to identify any relationships between these two traits and a variety of morphological traits. The final part of the experiment investigated how variation in these traits interacted with dilute acid pretreatment. Surprisingly lignin content did not significantly correlate with cell wall recalcitrance to enzymatic saccharification. Another important finding was that enzymatic saccharification without the pretreatment correlated with enzymatic saccharification after the pretreatment. General introduction and general materials and methods chapters are included. A final summary discussion chapter is also included in order to address the overall impact of these findings on biofuel potential.