Collaborative Proposal: MRA: Seasonality of photosynthesis of temperate and boreal conifer forests across North America

由于大气中二氧化碳(CO2)的增加，地球气候正在变暖，这主要是燃烧化石燃料为人类活动提供能源的结果。世界各地的森林正在帮助减缓大气的增加。与过去几十年相比，森林现在吸收了更多的二氧化碳，减缓了增长速度，造福了社会。为了应对气候变暖，许多地方的陆地植物光合作用的时间和大小正在发生变化，这使得人们很难预测森林碳循环反馈可能如何影响未来的气候。卫星遥感显示，整个北美的落叶林一般都通过延长生长季节来应对环境变化，春季落叶时间较早，秋季落叶时间较晚。然而，由于传统遥感技术的局限性，我们并不了解常绿针叶林对气候变暖的反应。科学家还需要更好地了解允许针叶树抵御寒冷冬季的生理过程。这项研究将把从树叶到林冠再到卫星的尺度上对针叶林反射和发射的光的观测联系起来，重点关注针叶林光合作用在空间和时间上的季节性。这项研究将利用国家生态观测网(NEON)在从佛罗里达到阿拉斯加的森林中建立的尖端科学基础设施。这项工作将记录在经历不同严重冬季的森林中发生的生理学变化，以完善和测试光合作用模型，以预测森林在缓解未来环境变化方面的关键作用。该项目将通过改进卫星遥感技术来量化北美各地针叶树光合作用的季节性，从而使生态科学家受益。该项目将通过在犹他州自然历史博物馆开展科学推广活动来吸引公众，提供互动资源，帮助游客将在自家后院观察到的变化与整个大陆类似的生态系统联系起来。植物经常暴露在比它们用于光合作用的阳光更多的阳光中，即使在天气有利的情况下，如果没有保护机制，组织可能会受到损害。植物已经进化出复杂的生理过程来安全地消散多余的阳光能量。在生长季节，这涉及叶黄素循环中类胡萝卜素色素的光依赖、可逆循环，这是整个植物界高度保守的光保护过程。然而，在寒冷的冬季，叶黄素色素参与了一个交替的、鲜为人知的不依赖光的过程，在白天和晚上都保持在光保护模式下。这两种光保护类型都涉及改变叶色的季节性色素和生理变化，并影响叶绿素分子的荧光发射。利用各种塔基和卫星仪器，这些生理变化可以通过植被反射的光(如光化学反射指数、叶绿素/类胡萝卜素指数等)和通过太阳诱导的荧光来检测。该项目的总体目标是利用霓虹灯和其他基础设施，量化北美各地针叶林的森林光合作用能力的空间和时间变异性。我们将把高时间和空间分辨率的植被反射率和荧光观测(基于塔的光谱)与基于塔的碳通量、针叶水平的光合作用和色素组成联系起来。这些数据将被吸收来改进和测试季节性森林光合作用的模型，并提供新的工具来启动大陆范围的观测框架，以量化30年霓虹灯生命周期内光合作用对环境变化的响应。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The climate of the Earth is warming due to increased carbon dioxide (CO2) in the atmosphere, a result primarily of combustion of fossil fuels to provide energy for human activities. Forests worldwide are helping to mitigate the atmospheric increase. Forests absorb more CO2 now than in prior decades, slowing the increase and benefiting society. In response to warming, the timing and magnitude of photosynthesis by land plants is changing in many locations, making it difficult to predict how forest carbon cycle feedbacks may affect future climate. Satellite remote sensing indicates that deciduous forests across North America have generally responded to environmental change by extending their growing season, with earlier spring leaf flush and later fall leaf drop. However, we do not understand how evergreen coniferous forests respond to warming because of limitations of traditional remote sensing techniques. Scientists also need better understanding of physiological processes that allow conifers to withstand cold winters. This study will link observations of reflected and emitted light from conifer forests at scales from leaf to forest canopy to satellite, to focus on seasonality of photosynthesis by conifer forests in space and time. The research will utilize cutting-edge scientific infrastructure built by the National Ecological Observatory Network (NEON) in forests from Florida to Alaska. This work will document the variations in physiology that occur in forests experiencing winters of varying severity, to refine and test models of photosynthesis to predict the critically important role of forests in mitigating future environmental change. This project will benefit ecological scientists by improving techniques in satellite remote sensing to quantify seasonality of conifer photosynthesis across North America. The project will engage the public by conducting science outreach efforts at the Natural History Museum of Utah, providing interactive resources to help visitors connect changes observed in their backyard to similar ecosystems across the continent.Plants are frequently exposed to more sunlight than they can use for photosynthesis, even when weather conditions are favorable, and without protective mechanisms, tissue damage would result. Plants have evolved elaborate physiological processes to safely dissipate excess sunlight energy. During the growing season, this involves light-dependent, reversible cycling of carotenoid pigments of the xanthophyll cycle, a highly-conserved photoprotective process across the plant kingdom. However, during cold winters, the xanthophyll pigments participate in an alternate, poorly-understood light-independent process, remaining in photoprotective mode during both the day and the night. Both photoprotective types involve seasonal pigment and physiological changes that alter leaf color, and affect fluorescence emission by chlorophyll molecules. Using a variety of tower- and satellite-based instruments, these physiological changes can be detected via light reflected from vegetation (as the photochemical reflectance index, the chlorophyll/carotenoid index, and others) and via solar-induced fluorescence. The project's overall objective is to quantify spatial and temporal variability in forest photosynthetic capacity of conifer forests across North America, using NEON and other infrastructure. We will link observations of vegetation reflectance and fluorescence with high temporal and spatial resolution (tower-based spectroscopy) to tower-based carbon fluxes, conifer-needle-level photosynthesis and pigment composition. These data will be assimilated to refine and test models of seasonal forest photosynthesis and provide new tools to launch a continental-scale observational framework to quantify photosynthetic response to environmental change over the 30-year NEON lifetime.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.