Monitoring seasonal and diurnal changes in photosynthetic pigments with automated PRI and NDVI sensors

[摘要] The vegetation indices normalized difference vegetation index (NDVI) andphotochemical reflectance index (PRI) provide indicators of pigmentation andphotosynthetic activity that can be used to model photosynthesis from remotesensing with the light-use-efficiency model. To help develop and validatethis approach, reliable proximal NDVI and PRI sensors have been needed. Wetested new NDVI and PRI sensors, "spectral reflectance sensors" (SRS sensors; recently developed byDecagon Devices, during spring activation of photosynthetic activity inevergreen and deciduous stands. We also evaluated two methods of sensorcross-calibration – one that considered sky conditions (cloud cover) atmidday only, and another that also considered diurnal sun angle effects.Cross-calibration clearly affected sensor agreement with independentmeasurements, with the best method dependent upon the study aim and timeframe (seasonal vs. diurnal). The seasonal patterns of NDVI and PRI differedfor evergreen and deciduous species, demonstrating the complementary natureof these two indices. Over the spring season, PRI was most stronglyinfluenced by changing chlorophyll : carotenoid pool sizes, while over thediurnal timescale, PRI was most affected by the xanthophyll cycleepoxidation state. This finding demonstrates that the SRS PRI sensors canresolve different processes affecting PRI over different timescales. Theadvent of small, inexpensive, automated PRI and NDVI sensors offers new waysto explore environmental and physiological constraints on photosynthesis,and may be particularly well suited for use at flux tower sites. Widerapplication of automated sensors could lead to improved integration of fluxand remote sensing approaches for studying photosynthetic carbon uptake, andcould help define the concept of contrasting vegetation optical types.

[学科分类] 地球化学与岩石