Identifying drought resilient populations and genotypes of forest trees to address climate change

根据观测和预测的加拿大西部气候变化，树木抵御干旱条件的能力是森林健康和生产力的关键。这项研究计划有以下战略目标：(1)研究在缺水严重的选定森林生态系统中树种的抗旱机制；(2)利用有用的耐旱性状遗传组合发现基因类型和局部适应群体；(3)揭示权衡，在生长条件有利的情况下，更好地应对干旱时期的结构或生理适应可能会影响生长潜力，并确定这些权衡最小的基因类型。该研究计划建立在两种一般方法的基础上。首先，我们将使用成熟树木的年轮分析来回顾评估对干旱时期的反应(抗逆性、抗性和年生长率的恢复)。这项研究计划的一个新方面是，这些方法将应用于加拿大重要森林树种的长期基因测试种植园，这些树种在过去30年里经历了干旱时期。为了寻找在目前的种子收集和试验种植园中可能没有捕获到的其他基因类型，我们还将对暴露在高水分不足和频繁干旱条件下的天然林分进行采样。其次，我们的目标是发现在长期基因测试中观察到的干旱反应的潜在特征。为此，我们将在受控生长室环境中进行苗木实验，使用几十年前用于建立遗传田间试验的相同种子批，这些种子已在省和联邦种子库存档。这使我们能够对生理、水力和结构抗旱性状进行详细的测量，并调查它们的遗传力和遗传相关性。随后，在幼苗中发现的关于耐旱机制和权衡的详细性状数据可以与在田间条件下生长数十年的相同种群和基因型的树木生长和健康的田间数据进行验证。虽然这项研究计划的主要基本研究目标是发现耐旱机制，但这些信息将是在加拿大西部重新造林和树木改良计划中筛选耐旱种植蓄积物的基本信息。加拿大西部每年种植约2亿株树苗，拟议的项目可以通过利用这一重新造林活动来提高气候变化下人工林的遗传复原力和生产力，从而产生深远的好处。

The capacity of trees to withstand drought conditions is key to forest health and productivity under observed and projected climate change in western Canada. This research program has the following strategic objectives: (1) research drought resilience mechanisms of tree species in selected forest ecosystems where water deficits are high; (2) discover genotypes and locally adapted populations with a useful genetic portfolio of drought tolerance traits; and (3) reveal tradeoffs, where structural or physiological adaptations to better cope with drought episodes might impact growth potential when growing conditions are favorable, and identify genotypes where these tradeoffs are minimized. The research program builds on two general approaches. First, we will use tree ring analysis in mature trees to retrospectively assess response to drought episodes (resilience, resistance, and recovery of annual growth rates). A novel aspect of this research program is that these methods will be applied to long-term genetic test plantations of important Canadian forest tree species that have experienced drought episodes over the last 30 years. In search for additional genotypes that may not have been captured in current seed collections and test plantations, we will also sample natural stands exposed to high water deficits and frequent drought conditions. Second, we aim to discover the underlying traits that are responsible for drought response observed in long-term genetic field tests. For this purpose, we will carry out seedling experiments in controlled growth chamber environments using the same seed lots used to establish the genetic field trials decades ago, and which have been archived in provincial and federal seed banks. This allows us to carry out detailed measurements of physiological, hydraulic and structural drought tolerance traits and investigate their heritabilities and genetic correlations. The detailed trait data on drought tolerance mechanisms and tradeoffs discovered in seedlings can subsequently be validated against field data of tree growth and health of the same populations and genotypes grown for decades under field conditions. While this research program has primarily fundamental research goals in discovering drought tolerance mechanisms, the information will be essential to screen for drought tolerant planting stock in reforestation and tree improvement programs in western Canada. Approximately 200 million seedlings per year are planted in western Canada, and the proposed project could yield profound benefits by leveraging this reforestation activity to improve the genetic resilience and productivity of planted forests under climate change.