Genetic variation in leaf traits and gas exchange response to vapor pressure deficit in two contrasting conifer species

1. Mechanistically predicting the evolutionary response of tree species to climate change requires an understanding of genetic variation in relevant traits. Here we compared the phenotypic and genetic variation in the Leaf Economics Spectrum (LES) traits and the response of gas exchange to vapor pressure deficit (VPD) in lodgepole pine (Pico) and white spruce (Pigl), an early and a late successional species dominating the boreal forests of western Canada. 2. We measured gas exchange, foliar nitrogen, and lamina mass to area ratio in 697 app. 30-year-old trees in two field progeny trials. We analyzed the response of gas exchange rates to VPD using a novel quantitative genetic model, the function-valued trait approach. 3. Pico showed greater phenotypic variation in the LES traits and greater genetic variation in photosynthetic rate than Pigl, but the species showed no significant difference in their phenotypic correlations between the LES traits. Pico showed a less sensitive stomatal response to VPD than Pigl and no significant genetic variation in stomatal sensitivity. In contrast, Pigl showed a positive correlation between the genetic values of stomatal sensitivity to VPD and stomatal conductance under low VPD. 4. Our study region is projected to see an increase in VPD with climate change; the less sensitive and genetically diverse stomatal response to VPD in Pico could make this species more vulnerable to climate change-induced droughts.

1. 从机制层面预测树木物种对气候变化的进化响应，需先明确其相关性状的遗传变异。本研究以加拿大西部北方针叶林的两大优势演替物种——早期演替的扭叶松（lodgepole pine, Pico）与晚期演替的白云杉（white spruce, Pigl）为研究对象，比较了二者叶片经济谱（Leaf Economics Spectrum, LES）性状的表型与遗传变异，以及气体交换对水汽压亏缺（vapor pressure deficit, VPD）的响应。
2. 我们在两处野外子代测定林中，对697棵约30年生的林木开展了气体交换、叶片氮含量以及叶质量面积比的测定；同时采用一种新型定量遗传模型——函数值性状分析法（function-valued trait approach），分析了气体交换速率对VPD的响应。
3. 相较于白云杉（Pigl），扭叶松（Pico）在LES性状上表现出更高的表型变异，在光合速率上具有更高的遗传变异，但二者在LES性状间的表型相关性上无显著差异。
3. 扭叶松对VPD的气孔响应敏感性弱于白云杉，且其气孔敏感性无显著遗传变异；与之相反，白云杉的VPD气孔敏感性遗传值与低VPD下的气孔导度呈正相关。
4. 研究区域的未来气候预测显示，VPD将随气候变化升高；扭叶松对VPD的气孔响应敏感性更低且遗传多样性更高，这可能使其更易受气候变化引发的干旱胁迫影响。