Hu Yi, Guy Robert D, Klápště Jaroslav, Lu Xuyang, Soolanayakanahally Raju Y
Institute of Mountain Hazards and Environment, Chinese Academy of Sciences, No. 189 Qunxiannan street, 610213, Chengdu, Sichuan, China.
Forest and Conservation Sciences, Faculty of Forestry, University of British Columbia, 2424 Main Mall, V6T1Z4, Vancouver, BC, Canada.
Tree Physiol. 2025 Jul 1;45(7). doi: 10.1093/treephys/tpaf072.
Genotypic variation in nitrogen-use traits remains largely unexplored in trees on a range-wide scale, either in field studies or under controlled experiments. Understanding natural variation in nitrogen-related traits and their relationships to climate is essential for studying local adaptation and advancing breeding efforts. In this study, we took advantage of a large collection of black cottonwood genotypes covering a major portion of the species' natural range, to study the genetic variation in nitrogen isotope discrimination (Δ15N). Nearly 350 unrelated wild genotypes were grown under steady-state hydroponic conditions and analyzed for growth and Δ15N-related traits. Differences in biomass, root-to-shoot ratio, whole-plant and organ-level nitrogen percentages, and Δ15N were found between genotypes and populations. Leaf nitrogen percentage and root-to-shoot ratio were significantly correlated to geographic and climatic variables, implying natural selection for lower leaf nitrogen and lower root-to-shoot ratio in regions with longer growing seasons and a lower risk of drought. Root Δ15N and (less so) leaf Δ15N correlated with geographic and climatic variables, and measurements from either tissue provide a reasonable indication of plant nitrogen uptake efficiency. A genome-wide association study was conducted on leaf and root Δ15N, leaf nitrogen percentage and root-to-shoot ratio. The analysis identified a candidate gene encoding glutaminyl-tRNA synthetase linked to root Δ15N, but found no significant associations with genes involved in nitrate transport or assimilation. However, multiple associations were detected for root-to-shoot ratio and leaf nitrogen percentage, both of which affect isotope-based calculations of root nitrogen efflux/influx and leaf nitrogen assimilation activity.
在树木中，无论是在田间研究还是在控制实验中，氮利用性状的基因型变异在大范围尺度上仍 largely unexplored。了解氮相关性状的自然变异及其与气候的关系对于研究局部适应性和推进育种工作至关重要。在本研究中，我们利用了一大组覆盖该物种自然分布范围主要部分的黑杨基因型，来研究氮同位素分馏（Δ15N）的遗传变异。将近350个不相关的野生基因型在稳态水培条件下生长，并分析其生长和与Δ15N相关的性状。在基因型和种群之间发现了生物量、根冠比、全株和器官水平的氮百分比以及Δ15N的差异。叶片氮百分比和根冠比与地理和气候变量显著相关，这意味着在生长季节较长且干旱风险较低的地区，自然选择倾向于较低的叶片氮含量和较低的根冠比。根Δ15N以及（程度稍低的）叶Δ15N与地理和气候变量相关，并且来自任一组织的测量值都能合理地指示植物的氮吸收效率。对叶和根的Δ15N、叶片氮百分比和根冠比进行了全基因组关联研究。分析确定了一个与根Δ15N相关的编码谷氨酰胺-tRNA合成酶的候选基因，但未发现与参与硝酸盐运输或同化的基因有显著关联。然而，检测到根冠比和叶片氮百分比有多个关联，这两者都会影响基于同位素的根氮流出/流入计算和叶片氮同化活性。
