Effects of Temperature and Irradiance on Photosystem Activity during Alhagi sparsifolia Leaf Senescence
2012-07-30
Leaf senescence is a typical physiological phenomenon in deciduous plants. It has been reported that photosynthetic capacity was inhibited by photochemical activities of photosystem (PS) I and II, especially PSII activity. Chlorophyll a (Chl a) fluorescence has been used as a nondestructive quantification of the damage to the leaf photosynthetic apparatus under abiotic stresses. However, few studies have provided a comprehensive analysis of fast Chl a fluorescence transients during leaf senescence under field. It was observed that irradiance was the main factor triggering leaf senescence, but very little is known about other factors modulating autumn senescence although low temperature and the length of the dark period may control senescence in aspen.
To study the effects of temperature and irradiance on photosystem activity, researchers grew the desert plant Alhagi sparsifolia Shap. at transition zone between Cele oasis and the southern fringe of Taklamakan sandy desert and conducted experiments on A. sparsifolia. During the period of leaf senescence of A. sparsifolia, the maximum photochemical quantum yield measured as variable to maximum fluorescence ratio (Fv/Fm) remained relatively high, although the number of active reaction centres per cross section (RCs) decreased significantly. The efficiency of electron acceptors beyond the primary quinone acceptor (QA) decreased. The effect of temperature and irradiance on photosystem activity was maximum after 6 d. The results suggest that: 1) the down-regulation of photosystem activity was due to the decline of both RCs and electron acceptance between plastoquinone (PQ) and cytochrome (cyt) b6/f; 2) photosystem activity presented negative correlation with daily mean temperature; and 3) reduction of daily sunshine period and increase of temperature at noon can stimulate the speed of senescence.
The result has been published on Biologia Plantarum, 2012, 56(4): 785-788. The paper can be downloaded from http://www.springerlink.com/index/455X61K6G6427178.pdf.