%0 Articles
%T Studying the diurnal and seasonal acclimation of photosystem II using chlorophyll-a fluorescence
%A Porcar-Castell, Albert
%D 2008
%J Dissertationes Forestales
%V 2008
%N 69
%R doi:10.14214/df.69
%U http://dissertationesforestales.fi/article/1852
%X A small fraction of the energy absorbed in the light reactions of photosynthesis is re-emitted as chlorophyll-a fluorescence. Chlorophyll-a fluorescence and photochemistry compete for excitation energy in photosystem II (PSII). Therefore, changes in the photochemical capacity can be detected through analysis of chlorophyll fluorescence. Fluorescence techniques have been used to follow the diurnal and seasonal acclimation in  energy partitioning between photochemical and non-photochemical processes in PSII. Energy partitioning in PSII, estimated through chlorophyll fluorescence, can be used as a proxy of the plant physiological status, and measured at different spatial and temporal scales. However, a number of technical and theoretical limitations still limit the use of chlorophyll fluorescence data in the study of the acclimation of PSII. Accordingly, my aim was to study the diurnal and seasonal acclimation of PSII in field conditions through the development and testing of new chlorophyll fluorescence-based tools.

I developed a new model capable of following the acclimation of PSII to rapid fluctuations in light intensity, and used it to study the acclimation in the electron transport rate under fluctuating light. Additionally, I developed new chlorophyll fluorescence parameters to estimate the seasonal acclimation in the sustained rate constant of thermal energy dissipation and photochemistry, and used them to quantitatively evaluate the effect of light and temperature on the seasonal acclimation of PSII. The results indicated that light environment not only affected the degree but also the kinetics of response of the acclimation to temperature. Furthermore, zeaxanthin-facilitated thermal dissipation appeared to be the main mechanisms modulating the fraction of absorbed energy being dissipated thermally during winter in field Scots pine. Finally, I studied the integration between diurnal and seasonal acclimation mechanisms using a recently developed instrument MONI-PAM (Walz GmbH, Germany) capable of monitoring the energy partitioning in PSII both at the diurnal and seasonal time-scales.