Authors: K Eric Van Gaalen Lawrence B Flanagan Derek R Peddle
Publish Date: 2007/04/04
Volume: 153, Issue: 1, Pages: 19-28
Abstract
Moss samples from the FluxnetCanada western peatland flux station in the Boreal Region of Alberta were measured in the laboratory to obtain the net photosynthesis rate and chlorophyll fluorescence of the moss under controlled environmental conditions including the regulation of moss water content simultaneously with measurements of moss spectral reflectance One objective was to test whether the photochemical reflectance index PRI detected changes in moss photosynthetic lightuse efficiency that were consistent with shortterm minutes to hours changes in xanthophyll cycle pigments and associated changes in nonphotochemical quenching NPQ as recorded by chlorophyll fluorescence The rate of net photosynthesis was strongly inhibited by water content at values exceeding approximately 9 fresh weight/dry weight and declined as the water content fell below values of approximately 8 Chlorophyll fluorescence measurements of maximum photosystem II efficiency generally remained high until the water content was reduced from the maximum of about 20 to values of approximately 10–11 and then declined with further reductions in moss water content A significant linear decline in NPQ was observed as moss water content was reduced from maximum to low water content values There was a strong negative correlation between changes in NPQ and PRI These data suggest that PRI measurements are a good proxy for shortterm shifts in photosynthetic activity in Sphagnum moss A second objective was to test how accurately the water band index WBI ratio of reflectance at 900 and 970 nm recorded changes in moss water content during controlled laboratory studies Strong linear relationships occurred between changes in moss water content and the WBI although the slopes of the linear relationships were significantly different among sample replicates Therefore WBI appeared to be a useful tool to determine samplespecific water content without destructive measurementsThis research was part of the Fluxnet Canada Research Network and was supported by grants from the Natural Sciences and Engineering Council of Canada NSERC the Canadian Foundation for Climate and Atmospheric Sciences CFCAS BIOCAP Canada and the University of Lethbridge We thank Bruce Johnson and Ngaire Nix for help with some of the field and laboratory work
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