Monitoring the ongoing declines in biodiversity and ecosystem health is essential for formulating... more Monitoring the ongoing declines in biodiversity and ecosystem health is essential for formulating societal responses. The Group on Earth Observations Biodiversity Observation Network (GEO BON) was created in 2008 to develop a global monitoring network, but that is a huge task with much remaining work. Fortunately, satellite remote sensing can help by providing periodic, global data that is not otherwise available. Continued advances – many of which are discussed in this book’s 19 chapters – in science as well as sensor and computational technology have an increasingly important role. However, taking advantage of these requires bringing together a variety of elements and disciplines, and it is with this in mind that a conceptual system architecture is here suggested. Key elements of this cloud-based architecture include: explicit support for collaboration, particularly across disciplines, to facilitate development of new algorithms; access to a wide variety of data, including satelli...
Remotely sensed vegetation indices (RSVIs) can be used to efficiently estimate terrestrial primar... more Remotely sensed vegetation indices (RSVIs) can be used to efficiently estimate terrestrial primary productivity across space and time. Terrestrial productivity, however, has many facets (e.g., spatial and temporal variability, including seasonality, interannual variability, and trends), and different vegetation indices may not be equally good at predicting them. Their accuracy in monitoring productivity has been mostly tested in single-ecosystem studies, but their performance in different ecosystems distributed over large areas still needs to be fully explored. To fill this gap, we identified the facets of terrestrial gross primary production (GPP) that could be monitored using RSVIs. We compared the temporal and spatial patterns of four vegetation indices (NDVI, EVI, NIRV, and CCI), derived from the MODIS MAIAC data set and of GPP derived from data from 58 eddy-flux towers in eight ecosystems with different plant functional types (evergreen needle-leaved forest, evergreen broad-lea...
Biodiversity promotes ecosystem function as a consequence of functional differences among organis... more Biodiversity promotes ecosystem function as a consequence of functional differences among organisms that enable resource partitioning and facilitation. As the need for biodiversity assessments increases in the face of accelerated global change, novel approaches that are rapid, repeatable and scalable are critical, especially in ecosystems for which information about species identity and the number of species is difficult to acquire. Here, we present 'spectral diversity'-a spectroscopic index of the variability of electromagnetic radiation reflected from plants measured in the visible, near-infrared and short-wave infrared regions (400-2,400 nm). Using data collected from the Cedar Creek biodiversity experiment (Minnesota, USA), we provide evidence that the dissimilarity of species' leaf spectra increases with functional dissimilarity and evolutionary divergence time. Spectral diversity at the leaf level explains 51% of total variation in productivity-a proportion compara...
Most photosynthesis measurements involve remote determinations. In gas-exchange systems, includin... more Most photosynthesis measurements involve remote determinations. In gas-exchange systems, including those based on chambers, atmospheric gradients, and eddy correlation, photosynthesis determinations are remote in the sense that the measurements are based on effects of leaves, plants, or canopies on the gaseous environment. In radiation-based remote sensing, the subject of this chapter, photosynthesis determinations are based on interactions between leaves, plants, or canopies and the radiation environment. The wavelength bands potentially useful for measurements related to photosynthesis range from the visible through the thermal and microwave regions. While remote sensing generally connotes large-scale satellite measurements, radiation-based remote sensing can be effectively utilized to address questions in photosynthesis research ranging in spatial scale from the chloroplast to the globe.
ABSTRACT . Sunflower plants (Helianthus annuus L., cv. CGL 208) were field-grown in adjacent plot... more ABSTRACT . Sunflower plants (Helianthus annuus L., cv. CGL 208) were field-grown in adjacent plots of varying resource availability. Control plants received irrigation (on a 4–5 d interval) and high levels of fertilizer nitrogen. Nutrient-stress (N-stress) plants received control levels of irrigation but no nutrient amendments and were determined to be nitrogen-limited. Water-stress (H2O-stress) plants received control levels of fertilizer nitrogen, but no irrigation after approximately 6 weeks of plant growth. Both stress treatments reduced maximum and diurnal net photosynthesis (A) but resulted in different physiological or biochemical adjustments that tended to maintain or increase A per unit of resource (nitrogen or water) in shortest supply while decreasing the ratio of A per unit of abundant resource. Nutrient-stress reduced total foliar nitrogen, foliar chlorophyll, and initial and total RuBPCase activities, thereby enhancing or preserving photosynthetic nitrogen-use efficiency (NUE), defined as the maximum A observed per unit of leaf nitrogen, relative to the control and H2O-stress treatments. In addition, N-stress reduced photosynthetic water-use efficiency (WUE), defined as the ratio of A to stomatal conductance to water vapour (g). The slope of A versus g increased with H2O-stress. In addition, sunflower plants responded to H2O-stress by accumulating foliar glucose and sucrose and by exhibiting diurnal leaf wilting, which presumably provided additional improvements in photosynthetic WUE through osmoregulation and reduction of midday radiation interception respectively. Photosynthetic NUE was decreased by H2O-stress in that control levels of total nitrogen, foliar chlorophyll, and RuBPCase activities were maintained even after mean diurnal levels of A had fallen to less than 50% of the control level. We conclude that field-grown sunflower manages a trade-off between photosynthetic WUE and NUE, increasing use efficiency of the scarce resource while decreasing use efficiency of the abundant resource.
summary Reflectance changes at 531 nm, associated with the zeaxanthin-antheraxanthin-violaxanthin... more summary Reflectance changes at 531 nm, associated with the zeaxanthin-antheraxanthin-violaxanthin interconversion and the related thylakoid energization, are widespread among plant species. We evaluated an index based on 531 nm reflectance ('PRI', Photochemical ...
IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium
In advance of the FLEX mission, experimental studies are needed to better understand the factors ... more In advance of the FLEX mission, experimental studies are needed to better understand the factors driving Solar-Induced Fluorescence (SIF) emission from vegetation across different temporal and spatial scales. Here, we present findings from boreal (evergreen and deciduous) forest trees and Midwestern (annual) crops, illustrating effects of seasonal downregulation and drought on the fluorescence signals. Further work is needed to develop defensible, quantitative fluorescence measurements, and to partition the drivers of the fluorescence signals into effects of structure and physiology.
Thanks for the positive comments and useful suggestions. In the revisions, I have argued for a mo... more Thanks for the positive comments and useful suggestions. In the revisions, I have argued for a more integrated approach to optical sampling that includes SIF along with reflectance-based indices and other approaches. The influence of both APAR and downregulation on fluorescence signals have been mentioned, and additional references on SIF have been added. However, given the length of the review, a full discussion of all the SIF literature seemed beyond the scope of the current paper, particularly since most of that literature has not yet been fully integrated with reflectance-based approaches. Also, there remain practical and theoretical challenges to doing so (given the parallel history of the approaches and the ongoing need for more robust instrumentation). I leave integrated SIF-reflectance studies as a recommendation for future work, particularly in the context of radiative transfer modeling, with the flux tower network as an ideal testbed for advancing our understanding of the ...
Monitoring the ongoing declines in biodiversity and ecosystem health is essential for formulating... more Monitoring the ongoing declines in biodiversity and ecosystem health is essential for formulating societal responses. The Group on Earth Observations Biodiversity Observation Network (GEO BON) was created in 2008 to develop a global monitoring network, but that is a huge task with much remaining work. Fortunately, satellite remote sensing can help by providing periodic, global data that is not otherwise available. Continued advances – many of which are discussed in this book’s 19 chapters – in science as well as sensor and computational technology have an increasingly important role. However, taking advantage of these requires bringing together a variety of elements and disciplines, and it is with this in mind that a conceptual system architecture is here suggested. Key elements of this cloud-based architecture include: explicit support for collaboration, particularly across disciplines, to facilitate development of new algorithms; access to a wide variety of data, including satelli...
Remotely sensed vegetation indices (RSVIs) can be used to efficiently estimate terrestrial primar... more Remotely sensed vegetation indices (RSVIs) can be used to efficiently estimate terrestrial primary productivity across space and time. Terrestrial productivity, however, has many facets (e.g., spatial and temporal variability, including seasonality, interannual variability, and trends), and different vegetation indices may not be equally good at predicting them. Their accuracy in monitoring productivity has been mostly tested in single-ecosystem studies, but their performance in different ecosystems distributed over large areas still needs to be fully explored. To fill this gap, we identified the facets of terrestrial gross primary production (GPP) that could be monitored using RSVIs. We compared the temporal and spatial patterns of four vegetation indices (NDVI, EVI, NIRV, and CCI), derived from the MODIS MAIAC data set and of GPP derived from data from 58 eddy-flux towers in eight ecosystems with different plant functional types (evergreen needle-leaved forest, evergreen broad-lea...
Biodiversity promotes ecosystem function as a consequence of functional differences among organis... more Biodiversity promotes ecosystem function as a consequence of functional differences among organisms that enable resource partitioning and facilitation. As the need for biodiversity assessments increases in the face of accelerated global change, novel approaches that are rapid, repeatable and scalable are critical, especially in ecosystems for which information about species identity and the number of species is difficult to acquire. Here, we present 'spectral diversity'-a spectroscopic index of the variability of electromagnetic radiation reflected from plants measured in the visible, near-infrared and short-wave infrared regions (400-2,400 nm). Using data collected from the Cedar Creek biodiversity experiment (Minnesota, USA), we provide evidence that the dissimilarity of species' leaf spectra increases with functional dissimilarity and evolutionary divergence time. Spectral diversity at the leaf level explains 51% of total variation in productivity-a proportion compara...
Most photosynthesis measurements involve remote determinations. In gas-exchange systems, includin... more Most photosynthesis measurements involve remote determinations. In gas-exchange systems, including those based on chambers, atmospheric gradients, and eddy correlation, photosynthesis determinations are remote in the sense that the measurements are based on effects of leaves, plants, or canopies on the gaseous environment. In radiation-based remote sensing, the subject of this chapter, photosynthesis determinations are based on interactions between leaves, plants, or canopies and the radiation environment. The wavelength bands potentially useful for measurements related to photosynthesis range from the visible through the thermal and microwave regions. While remote sensing generally connotes large-scale satellite measurements, radiation-based remote sensing can be effectively utilized to address questions in photosynthesis research ranging in spatial scale from the chloroplast to the globe.
ABSTRACT . Sunflower plants (Helianthus annuus L., cv. CGL 208) were field-grown in adjacent plot... more ABSTRACT . Sunflower plants (Helianthus annuus L., cv. CGL 208) were field-grown in adjacent plots of varying resource availability. Control plants received irrigation (on a 4–5 d interval) and high levels of fertilizer nitrogen. Nutrient-stress (N-stress) plants received control levels of irrigation but no nutrient amendments and were determined to be nitrogen-limited. Water-stress (H2O-stress) plants received control levels of fertilizer nitrogen, but no irrigation after approximately 6 weeks of plant growth. Both stress treatments reduced maximum and diurnal net photosynthesis (A) but resulted in different physiological or biochemical adjustments that tended to maintain or increase A per unit of resource (nitrogen or water) in shortest supply while decreasing the ratio of A per unit of abundant resource. Nutrient-stress reduced total foliar nitrogen, foliar chlorophyll, and initial and total RuBPCase activities, thereby enhancing or preserving photosynthetic nitrogen-use efficiency (NUE), defined as the maximum A observed per unit of leaf nitrogen, relative to the control and H2O-stress treatments. In addition, N-stress reduced photosynthetic water-use efficiency (WUE), defined as the ratio of A to stomatal conductance to water vapour (g). The slope of A versus g increased with H2O-stress. In addition, sunflower plants responded to H2O-stress by accumulating foliar glucose and sucrose and by exhibiting diurnal leaf wilting, which presumably provided additional improvements in photosynthetic WUE through osmoregulation and reduction of midday radiation interception respectively. Photosynthetic NUE was decreased by H2O-stress in that control levels of total nitrogen, foliar chlorophyll, and RuBPCase activities were maintained even after mean diurnal levels of A had fallen to less than 50% of the control level. We conclude that field-grown sunflower manages a trade-off between photosynthetic WUE and NUE, increasing use efficiency of the scarce resource while decreasing use efficiency of the abundant resource.
summary Reflectance changes at 531 nm, associated with the zeaxanthin-antheraxanthin-violaxanthin... more summary Reflectance changes at 531 nm, associated with the zeaxanthin-antheraxanthin-violaxanthin interconversion and the related thylakoid energization, are widespread among plant species. We evaluated an index based on 531 nm reflectance ('PRI', Photochemical ...
IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium
In advance of the FLEX mission, experimental studies are needed to better understand the factors ... more In advance of the FLEX mission, experimental studies are needed to better understand the factors driving Solar-Induced Fluorescence (SIF) emission from vegetation across different temporal and spatial scales. Here, we present findings from boreal (evergreen and deciduous) forest trees and Midwestern (annual) crops, illustrating effects of seasonal downregulation and drought on the fluorescence signals. Further work is needed to develop defensible, quantitative fluorescence measurements, and to partition the drivers of the fluorescence signals into effects of structure and physiology.
Thanks for the positive comments and useful suggestions. In the revisions, I have argued for a mo... more Thanks for the positive comments and useful suggestions. In the revisions, I have argued for a more integrated approach to optical sampling that includes SIF along with reflectance-based indices and other approaches. The influence of both APAR and downregulation on fluorescence signals have been mentioned, and additional references on SIF have been added. However, given the length of the review, a full discussion of all the SIF literature seemed beyond the scope of the current paper, particularly since most of that literature has not yet been fully integrated with reflectance-based approaches. Also, there remain practical and theoretical challenges to doing so (given the parallel history of the approaches and the ongoing need for more robust instrumentation). I leave integrated SIF-reflectance studies as a recommendation for future work, particularly in the context of radiative transfer modeling, with the flux tower network as an ideal testbed for advancing our understanding of the ...
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