Seasonal characteristics of chlorophyll fluorescence kinetics of heteromorphic leaves in Populus Euphratica

Populus euphratica Oliver grown in desert areas have polymorphic leaves, which include lanceolate to serrate oval leaves. This paper measures the chlorophyll fluorescence-induction kinetics curves of two types of heteromorphic leaves (lanceolate and serrate oval) of P. euphratica over the growth season in the Ejina Desert area, China. This is in order to study the electron transport, as well as absoprtion, distribtution, and dissipation of light energy and their adaptation characteristics. The results indicate that (1) serrate oval leaves' photosystem II (PSII) initial light-energy-conversion efficiency (Fv/Fm), potential activity (Fv/F₀), and the light-energy-utilization parameter (PI) are higher than those of lanceolate leaves; the accumulated amount of Q_A-(Vj) and the relative speed of Q_A deoxidation (M₀) are lower than those of lanceolate leaves; (2) the reaction center density (RC/CS₀) and electron-transfer energy (ET₀/CS₀) in the unit cross-sectional area of serrate oval leaves are higher than those of lanceolate leaves; the energy consumed in unit cross-sectional area (DI₀/CS₀), and energy-flow parameters (ABS/RC, ET₀/RC, TR₀/RC, and DI₀/RC) in the unit reaction center of serrate oval leaves are lower than those of lanceolate leaves; (3) the proportion of energy used for photochemical reaction and energy electron transport in serrate oval leaves (Φ_P0, Ψ₀, and Φ_E0) are larger than those in lanceolate leaves, and the maximum quantum yield (Φ_D0) of nonphotochemical reaction is less than that of lanceolate leaves. Thus, serrate oval leaves of P. euphratica have a more efficient energy-distribution strategy and better adaptability to extreme environmental conditions than lanceolate leaves.