Ecophysiology of northern forests: scaling physiological processes and states in space and time

小规模的生态生理过程可以对陆地碳循环产生大范围的影响。作为我参与和领导FLUXNET-加拿大和加拿大碳计划研究网络的补充，我建议开展研究，重点提高我们在叶和冠层水平上使用生理过程和状态的测量来在更大的空间尺度上评估这些过程的能力。我提出了三个相辅相成的研究领域，以解决碳循环科学中的一些关键知识空白。(1)我们将研究如何将北方森林植被的动态光谱特征与其光合光利用效率(LUE)联系起来。我们将在魁北克通量站点增加光谱反射率和叶面色素的测量，以便更好地了解不同胁迫水平和物候发育阶段下日照和阴影冠层部分对LUE的贡献。这可能会导致一种稳健的方法来衡量LUE。(2)我们将使用机载和星载激光雷达在大空间尺度上测试不同的森林生物量评估方法，从而获得更可靠的北方生态系统地上自养呼吸的估计。我们将评估采样的不同方面(例如，覆盖类型、坡度)在多大程度上推动了可变性。然后，我们将使用这些信息将卫星测量结果按省、国和环极尺度进行调整。(3)我们将使用我们的通量塔数据来评估衡量冻融事件的方法及其在地方到区域尺度上的生理意义。我们将通过将我们通量站点的生理过程和环境条件与从卫星微波传感器获得的冻融数据产品相联系来实现这一点。这将使我们能够研究冰冻和融化的严重程度、持续时间和分布如何与我们通量地点的光合作用和呼吸通量有关。它还将使我们能够确定这些冻融动态与我们作为加拿大碳计划的一部分进行的高精度二氧化碳浓度测量所采样的数千平方公里足迹之间的关系。

Small-scale ecophysiological processes can have large-scale impacts on terrestrial carbon cycling. As a complement to my participation and leadership in the Fluxnet-Canada and Canadian Carbon Program Research Networks, I propose research focused on improving our ability to use measurements of physiological processes and states at the leaf and canopy level to evaluate these processes at larger spatial scales. I propose three complementary areas of study that address some key knowledge gaps in carbon cycle science. (1) We will examine how we might link the dynamic spectral characteristics of boreal forest vegetation to its photosynthetic light use efficiency (LUE). We will add measurements of spectral reflectance and foliar pigments at our Quebec flux sites so as to better understand the contributions of sunlit and shadow canopy fractions to LUE under different levels of stress and stages of phenological development. This could lead to a robust methodology for scaling LUE. (2) We will test different approaches for evaluating forest biomass at large spatial scales using an airborne and a satellite-based lidar and thereby obtain more reliable estimates of aboveground autotrophic respiration for northern ecosystems. We will assess the extent to which different aspects of the sampling (e.g., cover type, slope) drive the variability. We will then use this information to scale the satellite measurements to provincial, national, and circumpolar scales. (3) We will use our flux tower data to evaluate methods for scaling freeze-thaw events and their physiological implications at local to regional scales. We will do this by linking physiological processes and environmental conditions at our flux sites to freeze-thaw data products obtained from a satellite-based microwave sensor. This will allow us to examine how the severity, duration, and distribution of freezing and thawing across a landscape relates to the photosynthetic and respiratory fluxes at our flux sites. It will also allow us to determine how these freeze-thaw dynamics relate to the several thousand square km footprints sampled by the high-precision carbon dioxide concentration measurements we are making as part of the Canadian Carbon Program.