Responses of the reflectance indices PRI and NDVI to experimental warming and drought in European shrublands along a north-south climatic gradient |
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Authors: | Pille Mä nd,Lea Hallik,Josep Peñ uelas,Pierpaolo Duce,Claus Beier,Já nos Garadnai,Inger Kappel Schmidt,Patricia Prieto,Joke W. Westerveld |
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Affiliation: | a Department of Botany, Institute of Ecology and Earth Sciences, University of Tartu, Lai, 40, Tartu 51005, Estonia b Department of Plant Physiology, Institute of Agricultural and Environmental Sciences, Estonian University of Life Sciences, Kreutzaldi 1, Tartu 51014, Estonia c Ecophysiology and Global Change Unit CSIC-CEAB-CREAF, CREAF (Center for Ecological Research and Forestry Applications), Edifici C, Universitat Autònoma de Barcelona, 08193 Bellaterra, Barcelona, Spain d Tartu Observatory, Tõravere, Estonia e Institute of Biometeorology, Consiglio Nazionale delle Ricerche, CNR-IBIMET, Via Funtana di lu colbu 4/a, 07100, Sassari, Italy f Centre for Ecology and Hydrology—Bangor, Environment Centre Wales, Deiniol Rd., Bangor, Gwynedd LL57 2UW, United Kingdom g RISØ National Laboratory, P.O. Box 49, DK-4000 Roskilde, Denmark h Institute of Ecology and Botany, Hungarian Academy of Sciences, H-2163 Vácrátót, Alkotmány u. 2-4, Hungary i Department of Plant Taxonomy and Ecology, Institute of Biology, Loránd Eötvös University, H-1117 Budapest, Pázmány P.s. 1/c, Hungary j Forest & Landscape Denmark, Copenhagen University, Hørsholm Kongevej 11, DK-2970 Hørsholm, Denmark k Institute for Biodiversity and Ecosystem Dynamics (IBED), University of Amsterdam, Nieuwe Achtergracht 166, 1018 WV Amsterdam, The Netherlands |
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Abstract: | The aim of this study was to evaluate the use of ground-based canopy reflectance measurements to detect changes in physiology and structure of vegetation in response to experimental warming and drought treatment at six European shrublands located along a North-South climatic gradient. We measured canopy reflectance, effective green leaf area index (green LAIe) and chlorophyll fluorescence of dominant species. The treatment effects on green LAIe varied among sites. We calculated three reflectance indices: photochemical reflectance index PRI [531 nm; 570 nm], normalized difference vegetation index NDVI680 [780 nm; 680 nm] using red spectral region, and NDVI570 [780 nm; 570 nm] using the same green spectral region as PRI. All three reflectance indices were significantly related to green LAIe and were able to detect changes in shrubland vegetation among treatments. In general warming treatment increased PRI and drought treatment reduced NDVI values. The significant treatment effect on photochemical efficiency of plants detected with PRI could not be detected by fluorescence measurements. However, we found canopy level measured PRI to be very sensitive to soil reflectance properties especially in vegetation areas with low green LAIe. As both soil reflectance and LAI varied between northern and southern sites it is problematic to draw universal conclusions of climate-derived changes in all vegetation types based merely on PRI measurements. We propose that canopy level PRI measurements can be more useful in areas of dense vegetation and dark soils. |
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Keywords: | green LAI, green Leaf Area Index green LAIe, effective projected green Leaf Area Index Fv/Fm, maximal photosynthetic efficiency of leaves LHCII, Light-Harvesting Complex of photosystem II NDVI, Normalized Difference Vegetation Index NDVI680, Normalized Difference Vegetation Index calculated from spectral regions at 780 nm and 680 nm NDVI570, Normalized Difference Vegetation Index calculated from spectral regions at 780 nm and 570 nm NPQ, non-photochemical quenching PAM, Pulse Amplitude Modulation PRI, Photochemical Reflectance Index PSII, Photosystem II qN, non-photochemical quenching ΦII, photosystem II quantum yield VI, Vegetation Index |
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