Abstract: A pot experiment was conducted to study the effects of light intensity (100%, 80%, 60%, 40%, and 20% of full light radiation) and exposure time (30, 60, 90, 120, and 150 days) on the leaf growth and physiological parameters of Boea clarkeana. With the decline of light intensity, the leaf morphological parameters (blade length and width, petiole length and diameter, and leaf area) of B. clarkeana decreased after an initial increase, with the maximum at 60% of full light radiation. Conspicuous injury on B. clarkeana leaves appeared under full light radiation, moderate to slight injury developed under 80% and 20% of full light radiation, while un-conspicuous injury was observed when the light intensity was 40% and 60% of full light radiation. The activities of antioxidant enzymes (CAT, SOD, and POD) were relatively low, and increased after an initial decrease with the decline of light intensity but showed a contrary trend with the increase of exposure time to light radiation. The activities of the antioxidant enzymes were the highest at full light radiation, and the lowest at 60% of full light radiation. The MDA content, proline content, and plasma membrane permeability increased after an initial decrease with the decline of light intensity, but increased significantly with the increase of exposure time. The chlorophyll content presented an increasing trend with the decline of light intensity, and increased after an initial decrease with the prolongation of exposure time. In sum, 40%-60% of full light radiation was beneficial, but weak and strong light radiations were adverse to B. clarkeana growth.

Key words: summer maize, quantity of bleeding sap in stalk, rind penetration strength, stalk microstructure, grain yield.