Physiological and Photosynthetic Characters of Polygonum Species in Response to Aluminum Stress

Two kinds of Polygonum species (Polygonum hydropiper and Polygonum lapathifolium) grown vigorously on acid soils were compared to investigate the physiological and photosynthetic responses under five Al³⁺ treatments (0, 25, 50, 100 and 400 mmol L^-1) in a hydroponic experiment. The results showed that under 400 mmol L^-1 Al³⁺, the malondialdehyde (MDA) content and transpiration rate (Tr) were significantly increased, and the proline content, activities of peroxides (POD) and catalase (CAT), net photosynthetic rate (Pn), water utilization efficiency (WUE), quantum yield of electron transport at PS II (fPS II) were decreased significantly in the two plant leaves, with photochemical quenching coefficient (q_p) and non-photochemical quenching coefficient (q_N) decreased only in P. hydropiper, compared to the control. However, under 25 and 50 mmol L^-1 Al³⁺, the MDA content decreased significantly, the proline content, activities of POD and CAT increased significantly, and the photosynthetic/chlorophyll fluorescence parameters did not inhibited, especially in P. lapathifolium. These results suggested that lower MDA content, more content of proline, higher activities of POD and CAT, and keeping proper function of photochemical system contributed to the tolerance to Al stress under low or middle Al concentrations, and P. lapathifolium was more tolerant than P. hydropiper.