Effects of high soil lead concentration on photosynthetic gas exchange and chlorophyll fluorescence in Brassica chinensis L.

Abstract

This study determined the effects of high soil lead concentration on photosynthetic gas exchange and chlorophyll fluorescence in Brassica chinensis L. Results showed the net photosynthetic rate, the maximum PSII quantum yield, photochemical quenching, and quantum yield of PSII photochemistry continuously increased until lead concentration reached 600 mg/kg. These parameters slightly decreased when lead concentration reached 900 mg/kg and significantly decreased when reached or exceeded 1200 mg/kg. As lead concentration increased, stomatal conductance and transpiration rate decreased; minimum fluorescence increased to different degrees; intercellular CO2 concentration initially decreased, increased, and then sharply decreased; and nonphotochemical quenching initially decreased and then increased. Therefore, soil treatment with 900 mg/kg lead can only slightly affect B. chinensis, whereas those with ≥ 1200 mg/kg can significantly affect this crop.