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

地球气候变暖是由于大气中二氧化碳（CO2）的增加，这主要是燃烧化石燃料为人类活动提供能量的结果。世界各地的森林正在帮助减缓大气的增加。森林现在比过去几十年吸收更多的二氧化碳，减缓了增长并使社会受益。为了应对气候变暖，许多地区陆地植物光合作用的时间和规模正在发生变化，这使得预测森林碳循环反馈如何影响未来气候变得困难。卫星遥感表明，北美各地的落叶林普遍通过延长其生长季节来应对环境变化，春季叶片较早冲洗，秋季叶片较晚脱落。然而，由于传统遥感技术的限制，我们并不了解常绿针叶林对变暖的响应。科学家们还需要更好地了解针叶树抵御寒冷冬季的生理过程。本研究将把针叶林从叶片到林冠再到卫星尺度的反射和发射光观测联系起来，重点研究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度冬季的森林中发生的生理变化，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重要作用。该项目将通过改进卫星遥感技术来量化北美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工作来吸引公众，提供互动资源，帮助游客将他们后院观察到的变化与整个大陆的类似生态系统联系起来。即使在天气条件有利的情况下，植物经常暴露在超过其光合作用能力的阳光下，如果没有保护机制，就会导致组织损伤。植物已经进化出复杂的生理过程来安全地消耗多余的阳光能量。在生长季节，这涉及到叶黄素循环中的类胡萝卜素依赖于光的可逆循环，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，叶黄素色素参与另一种鲜为人知的不依赖于光的过程，在白天和晚上都保持光保护模式。这两种光保护类型都涉及季节性色素和改变叶片颜色的生理变化，并影响叶绿素分子的荧光发射。利用各种基于塔和卫星的仪器，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）和太阳诱导的荧光来检测这些生理变化。该项目的总体目标是利用NEON和其他基础设施，量化北美针叶林森林光合能力的时空变化。我们将把具有高时空分辨率的植被反射率和荧光观测（塔基光谱）与塔基碳通量、针叶树水平的光合作用和色素组成联系起来。这些数据将被用于改进和测试季节性森林光合作用模型，并为启动大陆尺度观测框架提供新的工具，以量化30年NEON生命周期内光合作用对环境变化的响应。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。

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.