Collaborative Research: Environmental and biological controls on carbon uptake phenology in permafrost affected boreal forests

近几十年来，北方森林的快速变暖推动了多种生态系统的变化，包括永久冻土融化、非冻结季节延长和夏季变暖。这些变化对北方森林碳平衡的影响仍然高度不确定。越来越多的证据表明，由于土壤呼吸作用的增加，北方森林正在转变为二氧化碳的净来源。为了抵消这种碳的损失，生态系统依赖于植被通过植物光合作用持续吸收和积累碳。然而，目前尚不清楚环境条件，特别是湿度和温度，如何影响北方植物功能类型光合作用碳吸收的时间、持续时间和幅度（即光合物候学）。为了解决这些重要的知识空白，本研究侧重于阿拉斯加Caribou-Poker Creek （BONA）流域的树叶到流域的分析。具体来说，这项研究试图回答这样一个问题：“在受冻土影响的北方森林中，光合物候的环境和生物控制是什么？”这项研究将为本科生和研究生提供实地和实验室研究实践的培训。该项目还将与PolarTREC项目中的科学教育工作者合作，开发信息故事地图、教育视频和学习活动，以提高公众对寒带森林为社会提供的重要生态系统服务的认识。本研究将采用一种新颖的方法，将太阳诱导叶绿素荧光（SIF）的高频观测作为植被总初级生产力（GPP）的指标，并将l波段微波后向散射强度作为冠层含水量的指标。这些测量将由一系列观测加以补充，包括叶片和生态系统气体交换，以及沿着土壤-植被连续体的环境测量（例如，土壤温度、土壤湿度、水流速度）。观测结果将用于通过统计分析（例如，多变量自适应回归样条）确定林分和流域水平上发生的GPP与环境条件之间的关键功能关系。新获得的见解将用于利用遥感驱动的碳数据模型（CARDAMOM）优化数据和过程模型集成框架，并从BONA流域扩展到阿拉斯加和加拿大西北部的北方森林。CARDAMOM框架将使我们能够：(1)获得新的、观测受限的GPP区域估计；(2)评估不同气候情景下北方地区二氧化碳吸收的区域敏感性；(3)在气候变暖、生长季节延长和土壤水分条件变化的条件下，确定了北方森林GPP的汇潜力和变化轨迹。研究结果将是减少北方森林GPP预算估算不确定性的重要一步，并将有助于确定未来模型改进的优先事项。该项目由OPP北极自然科学项目和DEB生态系统科学项目共同资助。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Rapid warming in boreal forests has driven diverse ecosystem changes in recent decades, including permafrost thaw, longer non-frozen seasons, and warmer summers. The impact of these changes on the carbon balance of boreal forests remains highly uncertain. A growing body of evidence indicates that boreal forests are shifting toward being a net carbon dioxide source due to increases in soil respiration. To offset this loss of carbon, ecosystems rely on sustained vegetation uptake and accumulation of carbon through plant photosynthesis. However, it is unclear how environmental conditions, particularly moisture and temperature, affect the timing, duration and magnitude of photosynthetic carbon uptake (i.e., photosynthetic phenology) across boreal plant functional types. To address these important knowledge gaps, this study focuses on a leaf-to-watershed analysis at the Caribou-Poker Creek (BONA) Watershed in Alaska. Specifically, the study seeks to answer the question, “What are the environmental and biological controls of photosynthetic phenology in permafrost-affected boreal forests?” This research will provide training to undergraduate and graduate students in field and laboratory research practices. The project will also partner with science educators within the PolarTREC program to develop informational StoryMaps, educational videos, and learning activities to raise public awareness of the important ecosystem services that boreal forests provide to society. This study will use a novel approach that incorporates high-frequency observations of solar-induced chlorophyll fluorescence (SIF) as an indicator of vegetation gross primary productivity (GPP), and L-band microwave backscattering intensity as an indicator of canopy water content. These measurements will be complemented by a suite of observations including leaf and ecosystem gas exchange, and environmental measurements (e.g., soil temperature, soil moisture, water flow velocity) along a soil-to-vegetation continuum. The observation will be used to identify the key functional relationships between GPP and environmental conditions occurring at the stand and watershed levels through statistical analyses (e.g., multivariate adaptive regression splines). Newly gained insight will be used to optimize a data and process-model integration framework using the remote-sensing driven CARbon Data Model (CARDAMOM) and to extend from the BONA watershed to the boreal forests of Alaska and northwestern Canada. The CARDAMOM framework will allow us to: (1) obtain new, observation-constrained, regional estimates of GPP; (2) assess the regional sensitivity of boreal carbon dioxide uptake under various climate scenarios; and (3) identify the sink potential and trajectory of GPP in boreal forests, given the state of climate warming, a lengthening growing season, and changes in soil water conditions. The study results will be an important step forward in reducing uncertainty in GPP budget estimates for boreal forests, and will help set priorities for future model improvements. This project is co-funded by the OPP Arctic Natural Sciences Program and DEB Ecosystem Science Program.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.