Abstract: A pot experiment was conducted to study the impacts of Pb²⁺ and Cr⁶⁺ on the photosynthesis, nutritional quality, and food safety of water spinach (Ipomoea aquatica Forsk.) under simulated acid rain (AR) with different acidity. The results showed that under AR, the stress of test heavy metals on the photosynthesis and quality of the spinach decreased in the order Pb>Pb+Cr>Cr. With increasing acidity of AR, the impact of treatments AR+Pb and AR+Pb+Cr increased remarkably, and the stress effect of treatment AR+Pb+Cr was greater than that of the other treatments under pH=3.5. Compared with the control, three parameters of photosynthesis decreased with increasing acidity of AR, but had different susceptivity to the stress. The protein and free amino acid contents in the spinach had positive correlations with pH when the pH was <5.6, and, with increasing acidity, the soluble sugar content increased while reductive sugar content decreased, being a kind of response to the environmental stress. Treatments Pb and Pb+Cr notably promoted the nitrate nitrogen accumulation, and the nitrate nitrogen content in the spinach increased with the acidity of AR. There existed a competition between the adsorption of Pb and Cr in the spinach, and the enrichment of the two heavy metals would be sped up with decreasing acidity of AR.

Key words: Paper, Denitrification, Biological treatment, Nitrate