Cold-induced photoinhibition and winter leaf-loss in the broad-leaved tree Aristotelia serrata (Elaeocarpaceae)

Abstract

Relationships between cold-induced photoinhibition of photosynthesis and winter leaf-loss were investigated for leaves of a wineberry (Aristotelia serrata J. R. Forst. and G. Forst.) tree. Previous work identified consistent differences in leaf loss between shaded and exposed parts of wineberry trees, possibly related to the adverse effects of cold temperatures and high irradiance during winter frosts. Differences in leaf temperature and irradiance between shaded and exposed parts of a wineberry canopy were quantified, together with their relationships to decline and recovery of cold-induced photoinhibition of photosynthesis (measured by the ratio of variable to maximal chlorophyll fluorescence; F_v / F_m). These data, together with measurements of leaf loss from selected shoots, were used to test the hypothesis that leaf loss is greater from open than from shaded parts of wineberry canopies, and increases with decreases in F_v / F_m following winter frosts. F_v / F_m of leaves on exposed shoots was always significantly (P<0.001) lower than leaves on shaded shoots. The absolute difference in F_v / F_m ranged from 0.11 to 0.57. F_v / F_m declined markedly following periods of freezing leaf temperatures (T_l), but recovered after several days of non-freezing T_l. A multiple regression model, including terms for integrated irradiance (Q_i), minimum T_l, T_l at the time of F_v / F_m measurements, and the value of F_v / F_m, on the previous day explained 95% of the variability in daily F_v / F_m. Leaf loss was greater from exposed shoots (0.22 leaves shoot^–1 d^–1) than from shaded shoots (0.07 leaves shoot^–1 d^–1; P<0.001) and increased following frost-induced decreases in the value of F_v / F_m. Measured rates of leaf loss from exposed shoots were significantly related to F_v / F_m measured 14 d previously (r²=0.89, P<0.01), supporting our hypothesis.