Seasonal timing of fluorescence and photosynthetic yields at needle and canopy scales in evergreen needleleaf forests

作者：Zoe Pierrat, Troy S. Magney, Andrew J. Maguire, Logan Brissette, Russell Doughty, D. R. Bowling, Barry A. Logan, N. Parazoo, Christian Frankenberg, J. Stutz · 发表于：Ecology · 年份：2024 · DOI：10.1002/ecy.4402 · 被引用次数：21 · 研究领域：Plant Water Relations and Carbon Dynamics、Remote Sensing in Agriculture、Ecology and Vegetation Dynamics Studies

Abstract The seasonal timing and magnitude of photosynthesis in evergreen needleleaf forests (ENFs) has major implications for the carbon cycle and is increasingly sensitive to changing climate. Earlier spring photosynthesis can increase carbon uptake over the growing season or cause early water reserve depletion that leads to premature cessation and increased carbon loss. Determining the start and the end of the growing season in ENFs is challenging due to a lack of field measurements and difficulty in interpreting satellite data, which are impacted by snow and cloud cover, and the pervasive “greenness” of these systems. We combine continuous needle‐scale chlorophyll fluorescence measurements with tower‐based remote sensing and gross primary productivity (GPP) estimates at three ENF sites across a latitudinal gradient (Colorado, Saskatchewan, Alaska) to link physiological changes with remote sensing signals during transition seasons. We derive a theoretical framework for observations of solar‐induced chlorophyll fluorescence (SIF) and solar intensity‐normalized SIF (SIF relative ) under snow‐covered conditions, and show decreased sensitivity compared with reflectance data (~20% reduction in measured SIF vs. ~60% reduction in near‐infrared vegetation index [NIRv] under 50% snow cover). Needle‐scale fluorescence and photochemistry strongly correlated ( r 2 = 0.74 in Colorado, 0.70 in Alaska) and showed good agreement on the timing and magnitude of seasonal transitions. We demo...