Effects of water and phosphorus on chlorophyll fluorescence characteristics of different position leaves in Lespedeza daurica

A pot experiment was used to determine the Chlorophyll fluorescence characteristics of different position leaves in Lespedeza daurica under three different water level (80% FC, 60% FC and 40% FC) and two phosphorus treatments ( 0.1 Pgkg-1 dry soil and no P addition). The results of this study showed that the initial fluorescence (F0) and the maximum photochemical efficiency (Fv/Fm) of flag leaves were significantly lower those of middle leaves under moderate water stress and supply phosphorus, while there were no significant differences in maximal fluorescence (Fm), implying that the PSⅡreaction center of flag leaves were less destroyed than the middle leaf and the light energy transformation efficiency of flag leaves was higher. The leaf quenching coefficient (NPQ) significantly decreased and the Fv/Fm values of flag leaf and new leaf under moderate water stress condition were significantly higher in supply phosphorus treatment, indicating that the light energy dissipation decreased and light energy transformation increased under water stress by addition of phosphorus, which suggested that the supply phosphorus improved the adaptive capacity of L.daurica to semiarid loess hillygully region.