Spectral reflectance and photosynthetic properties of Sphagnum mosses exposed to progressive drought

This article explores the utility of spectral reflectance signals to assess changes in the photosynthetic efficiency (Phi(PSII)) of Sphagnum mosses exposed to reductions in water availability. Reflectance was measured in parallel to moisture content and chlorophyll fluorescence in five species of Sphagnum exposed to progressive drought. Decreases in moisture availability caused a significant reduction in Phi(PSII) for all samples tested. An objective was to ascertain whether Sphagnum Phi(PSII) was better correlated With (i) spectral indices directly related to photosynthetic processes though association with xanthophyll cycle pigmentation (the photochemical reflectance index: PRI). or (ii) indices indirectly correlated with photosynthetic activity but able to detect changes in canopy morphology (the normalized difference vegetation index; NDVI), chlorophyll stability (the structure insensitive pigment index: SIPI). or canopy moisture content (the floating water band index; fWBI). Strongest correlations were found between Phi(PSII) and indices which were indirectly related to Phi(PSII). Both the SIPI and the NDVI exhibited linear correlations although these relationships were sometimes sample-specific. The fWBI was the index least affected by sample-specific relationships and showed a strong curvilinear correlation with Phi(PSII). Photosynthetic efficiency was correlated With the PRI but relationships were much weaker than for the other indices used, and in some cases negative. The NDVI and the fWBI shoal the most potential for monitoring! Sphagnum photosynthetic activity at the ecosystem scale. The results from this Study Will help to monitor and understand the responses of these key species to hydrological disturbances. Copyright (C) 2008 John Wiley & Sons, Ltd.