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Observations of Sun-Induced Chlorophyll fluorescence (SIF), Photochemical Reflectance Index (PRI) and Chlorophyll:Carotenoid Index (CCI) during spring recovery in two evergreen conifers from the Boreal Forest.

  • Author / Creator
    Campos Valverde, Rebeca
  • Northern hemisphere evergreen forests assimilate a significant fraction of global atmospheric CO2. Conifers undergo winter-downregulated photosynthetic activity and spring-onset photosynthetic activation. Currently, increased temperatures are leading to shifts in photosynthetic phenology (early spring-onset, longer growing season), which has important implications in terrestrial GPP. How these species are adapting to these changes is highly uncertain. Evergreen conifer’s foliage remains green year-round, making the photosynthetic transition between spring and winter “invisible” to classical remote sensing (RS) techniques such as the Normalized Difference Vegetation Index (NDVI). However, conifers adjust their carotenoid pigment content between seasons, to modulate photosynthesis and relieve excess energy. These changes can be detected using a series of RS techniques such as the Photochemical Reflectance Index (PRI), the Chlorophyll/Carotenoid Index (CCI) and the Sun induced chlorophyll fluorescence signal (SIF). To better understand the mechanisms and timing of this invisible transition, we conducted a series of leaf-scale experiments to explore the biophysical link between SIF, PRI, CCI and air temperature in two dominant conifer species: lodgepole pine (Pinus contorta) and black spruce (Picea mariana), in Alberta, Canada. Our results provide strong evidence that during the spring recovery, SIF parameters, and carotenoid reflectance-based vegetation indices are closely tied to temperature changes and positively correlated with each other. We were able to track the relative-timing of the photosynthetic reactivation of both species during the spring recovery and we gained knowledge about how these two conifer species’ metrics differ slightly in kinetics. In particular, the activation of SIF emission was earlier in lodgepole pine (P. contorta) than in black spruce (P. mariana). We conclude that together these metrics are reliable optical methods for detecting spring transition across evergreen conifer tree species and can help lay the foundation for improved remote sensing methods of monitoring the changing photosynthetic activity of boreal forests. These findings are important because the boreal ecosystem is a major contributor to the global climate system. Thus, reducing uncertainties in the timing and drivers of the spring transition could generate a better understanding of how this biome is responding to a changing climate, and how it may in turn affect climate.

  • Subjects / Keywords
  • Graduation date
    Fall 2022
  • Type of Item
    Thesis
  • Degree
    Master of Science
  • DOI
    https://doi.org/10.7939/r3-jtke-4731
  • License
    This thesis is made available by the University of Alberta Library with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.