Effects of grass coverage management on photosynthetic characteristics of apple leaves during leaf expanding

To explore the difference of photosynthetic characteristics during leaf expanding of apple leaves under different orchard floor managements, the photosynthetic and fluorescence parameters during leaf expanding of 5 a apple orchard under grass coverage and bare earth conditions were determined by gas exchange and chlorophyll a fluorescence kinetics. The results showed that chlorophyll contents, Pn, PICS and ΔI of leaves under grass coverage and bare earth conditions were significantly lower at early stage of leaf expansion than that of expanded leaves (EL). Pn were 26.9% and 18.4% of EL, PICS were 67.7% and 53.4% of EL, and ΔI were 35.6% and 30.5% of EL, respectively. Chlorophyll contents, Pn, PICS and ΔI of leaves under grass coverage condition were significantly higher than that under bare earth condition at early stage of leaf expansion. In conclusion, the PSII function have developed to some extent at early stage of leaf expansion under grass coverage and bare earth conditions, but developing extent of PSⅠ function was lower than PSⅡ function. Grass coverage could improve development of PSⅡ and PSⅠ function, and thus enhance leaf photosynthetic efficiency.