Boreal forests on permafrost: functional trait and whole-plant responses to climate warming and permafrost thaw

永久冻土上的北方森林：功能特征和全植物对气候变暖和永久冻土融化的响应

• 批准号: RGPIN-2014-06433
• 负责人: Baltzer, Jennifer
• 金额: $ 1.97万
• 依托单位: Wilfrid Laurier University
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2016
• 资助国家: 加拿大
• 起止时间: 2016-01-01 至 2017-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=612217
• 关键词: Boreal; forests; permafrost; functional; trait

Much of Canada’s boreal forest biome occurs on permafrost (perennially cryotic ground). In Northwestern Canada, these forests are changing rapidly due to recent climate warming (~3°C in the last 50 years) and associated permafrost thaw, which could have global implications due to the large amounts of carbon stored in these systems. Despite this, we know relatively little about the ecology of these forests due in part to their limited commercial value and relative inaccessibility. Increased atmospheric CO2 concentrations and associated warming are predicted to increase productivity and the northward extent of boreal forests via: (a) longer growing seasons; (b) increased soil temperatures, which alter freeze-thaw dynamics in seasonally frozen as well as permafrost soils and enhance soil microbial activity, decomposition, and nutrient mineralization; and (c) enhanced physiological rates attributable to elevated atmospheric CO2 concentrations. Recent studies have shown that contrary to predictions, high latitude boreal forests are showing substantial negative responses to changing environmental conditions and through the proposed research we seek to better understand why these changes are happening to improve our capacity to predict future conditions. To achieve this goal, we will quantify growth-climate relationships of dominant tree species across a latitudinal and permafrost gradient in the Northwest Territories (NWT), Canada using tree ring studies. Sampling will be conducted with a view to capturing local variability in soil resource conditions to determine the role of soil resource availability in observed growth-climate relationships (i.e., are negative tree growth responses to warming temperatures due to resource limitation?). Tree rings contain information not only on the rates of growth, but also the environmental conditions at the time the wood was formed and physiological potential of individuals as measured through tree ring anatomy and associated stable isotope composition of the rings. For trees showing different responses to recent climate change, we will therefore conduct detailed tree ring anatomical and stable isotope analyses to discern the differential anatomical and physiological drivers of growth responses. Finally, we wish to link these long temporal records with actual flux rate and productivity. To achieve this, we will quantify associated physiological traits within sites and across the latitudinal gradient to determine relationships between structure and function. My proposed research will elucidate the mechanisms driving high latitude boreal forest responses to climate changes, and how these responses vary with latitude and permafrost conditions, local soil conditions, and species. Our data will provide novel insights to the physiological mechanisms driving growth responses in high latitude trees. This understanding is crucial for evaluating the range of plasticity and the capacity for resilience of trees growing under changing environmental conditions and ultimately to predict community and species level responses of high latitude boreal forests under future climatic scenarios.

加拿大北方森林生物群落的大部分都位于永久冻土层（常年冰冻的地面）。在加拿大西北部，由于最近的气候变暖（过去50年约3°C）和相关的永久冻土融化，这些森林正在迅速变化，由于这些系统中储存了大量的碳，这可能会对全球产生影响。尽管如此，我们对这些森林的生态知之甚少，部分原因是它们的商业价值有限，而且相对难以进入。预计大气CO2浓度的增加和相关的变暖将通过以下方式增加北方森林的生产力和向北延伸：（a）生长季节延长;（B）土壤温度升高，改变季节性冻土和永久冻土的冻融动态，并增强土壤微生物活动、分解和养分矿化;以及（c）归因于大气CO2浓度升高的生理速率增强。最近的研究表明，与预测相反，高纬度北方森林对不断变化的环境条件表现出实质性的负面反应，通过拟议的研究，我们试图更好地了解为什么会发生这些变化，以提高我们预测未来条件的能力。 为了实现这一目标，我们将量化的主要树种在纬度和冻土梯度在西北地区（NWT），加拿大使用树木年轮研究的生长-气候关系。取样的目的是捕捉当地土壤资源条件的变异性，以确定土壤资源可利用性在观测到的生长-气候关系中的作用（即，是负树生长反应变暖的温度，由于资源限制？）。树木年轮不仅包含关于生长速度的信息，而且还包含木材形成时的环境条件以及通过树木年轮解剖学和年轮相关稳定同位素组成测量的个体生理潜力。因此，对于对近期气候变化表现出不同反应的树木，我们将进行详细的树木年轮解剖和稳定同位素分析，以辨别生长反应的差异解剖和生理驱动因素。最后，我们希望将这些长期的时间记录与实际的流量和生产力联系起来。为了实现这一目标，我们将量化相关的生理特征内的网站和整个纬度梯度，以确定结构和功能之间的关系。我提出的研究将阐明高纬度北方森林对气候变化的反应机制，以及这些反应如何随纬度和永久冻土条件，当地土壤条件和物种而变化。我们的数据将提供新的见解的生理机制驱动高纬度树木的生长反应。这种理解是至关重要的可塑性和适应能力的树木生长在不断变化的环境条件下，并最终预测未来气候情景下的高纬度北方森林的社区和物种水平的反应。