Abstract: A cucumber cv.‘JinYou35’was chosen as an experimental material to examine the effects of shading on the photosynthetic parameters and fluorescence parameters of the young cucumber leaves. Four levels of light intensity were set in greenhouse during 25 days which comprise full light intensity(CK), 20% of full light intensity(T1), 40% of full light intensity(T2) and 60% of full light intensity(T3). The results showed that: shading make the content of chlorophyll a, chlorophyll b and total chlorophyll increased in different degrees, while the value of chlorophyll a/b decreases. After shading 25 days, the content of chlorophyll a under the block 60%, 40%, 20% of the light were 30.6%, 16.5%, 15.4% higher than the control treatment respectively. The light saturation point(LSP), maximum photosynthetic rate (Pmax) and the apparent quantum efficiency (AQE) of young cucumber leaves which under shade processing decreased, while the light compensation point (LCP) increased with the increase of the days of treatment. Treating after 25 days, the stomatal conductance（Gs）of blocking 60%, 40%, 20% of light were 57.9%, 57.4%, 47.3% smaller than the controlled treatment respectively, and the transpiration rates(Tr) were 34.7%, 34.0% and 52.4% lower than the controlled treatment respectively. With the increase of the days of treatment, the stomatal limitation (Ls) and water use efficiency (WUE) of cucumber leaves were shown an increasing trend. The potential efficiency of photosystem II (Fv/Fm) of shading cucumber leaves shown a downtrend roughly with the increased of shading days, and the photochemical quenching (qP) decreased, while the non-photochemical quenching (qN) increased. The study confirmed that shading made the chlorophyll content of cucumber leaves increased, affected photosynthesis.

Key words: Low light level, Cucumber, Chlorophyll, Photosynthetic characteristics, Fluorescence parameters