Tree growth, wood properties and saccharification traits in SwAsp Populus tremula trees grown in Ekebo Sweden

Background Wood represents the majority of the biomass on land and constitutes a renewable source of biofuels and other bioproducts. However, wood is recalcitrant to bioconversion, raising a need for feedstock improvement in production of, for instance, biofuels. We investigated the properties of wood that affect bioconversion, as well as the underlying genetics, to help identify superior tree feedstocks for biorefining. Results We recorded 65 wood-related and growth traits in a population of 113 natural aspen genotypes from Sweden. These traits included three growth and field performance traits, 20 traits for wood chemical composition, 17 traits for wood anatomy and structure, and 25 wood saccharification traits as indicators of bioconversion potential. Glucose release after saccharification with acidic pretreatment correlated positively with tree stem height and diameter and the carbohydrate content of the wood, and negatively with the content of lignin and the hemicellulose sugar units. Most of these traits displayed extensive natural variation within the aspen population and high broad-sense heritability, supporting their potential in genetic improvement of feedstocks towards improved bioconversion. Finally, a genome wide association study (GWAS) revealed 13 genetic loci for saccharification yield (on a whole tree biomass basis), with six of them intersecting with associations for either height or stem diameter of the trees. Conclusions The simple growth traits of stem height and diameter were identified as good predictors of wood saccharification yield in aspen trees. GWAS elucidated the underlying genetics, revealing putative genetic markers for bioconversion of bioenergy tree feedstocks.

研究背景：木材是陆地生物质的主要组成部分，同时也是生物燃料及其他生物基产品的可再生来源。然而木材的生物转化过程存在顽固抗性，这使得在生物燃料等产品的生产中亟需对原料进行改良。本研究针对影响生物转化的木材特性及其潜在遗传机制展开探究，以期为生物炼制筛选优良的林木原料。

研究结果：我们对来自瑞典的113个天然山杨基因型群体中的65项木材相关及生长性状进行了记录。该类性状涵盖3项生长与田间表现性状、20项木材化学组成性状、17项木材解剖结构性状，以及25项作为生物转化潜力指标的木材糖化（saccharification）性状。经酸性预处理后的糖化步骤所释放的葡萄糖量，与树木茎秆高度、直径及木材碳水化合物含量呈正相关，而与木质素含量及半纤维素糖单元含量呈负相关。该群体中多数性状表现出丰富的自然变异，且具有较高的广义遗传力（broad-sense heritability），这表明这些性状可用于通过遗传改良提升原料的生物转化效率。最后，全基因组关联分析（genome wide association study, GWAS）共鉴定出13个与基于全树生物量的糖化产量相关的遗传位点，其中6个位点同时与树木株高或茎径的关联信号存在重叠。

研究结论：本研究鉴定出茎高与茎径这两项简易生长性状可作为山杨木材糖化产量的良好预测指标。全基因组关联分析阐明了其潜在的遗传机制，为能源林木原料的生物转化筛选出潜在的遗传标记。