Chlorophyll a fluorescence imaging of grassland species in a warmer climate

Abstract

Despite its relevance to carbon sequestration of ecosystems, the effects of climate change on leaf senescence and stress are not well known. A warmer climate may affect autumn physiology, leaf senescence, and stress physiology of plants in the future. This study made use of grassland model ecosystems in twelve sunlit, climate-controlled chambers. Half of the model ecosystems were subjected to an air temperature increase of 3 degrees C. In each chamber, 24 plant communities were grown, containing one or more grassland species. Two of those species, Rumex acetosa and Plantago lanceolata were studied during autumn. Almost no leaf senescence was visible for Plantago lanceolata, while a large proportion of the sample leaves of Rumex acetosa senesced and died during the measurement period. This proportion was larger under elevated temperature. The physiological status of the plants was assessed by means of chlorophyll a fluorescence measured with a Plant Efficiency Analyser (Hansatech). Every two weeks, measurements were made in the morning on attached, dark adapted leaves. Additionally, images of chlorophyll a fluorescence of leaves of Rumex acetosa were taken on two dates using a prototype transportable fluorescence imaging system (Ciscato et al., unpublished). Statistical analysis of those images will be discussed. Analysis of chlorophyll fluorescence induction curves showed a gradual decrease of the yield of primary photochemistry through time for both species. Although the ratio Fv/Fm was not different between treatments, several other parameters characterizing the fast kintetics of the fluorescence rise were significantly affected by the warmer climate. Evidence was obtained that elevated temperature increased the efficiency of electron transport after the reduced quinone A. Interestingly, this positive effect disappeared for Rumex acetosa at the time of visible leaf senescence. Fluorescence signals will be discussed in detail in combination with digital images and photosynthesis to explain end-of-season physiology in a warmer climate.