Effect of chromium and nitrogen form on photosynthesis and anti-oxidative system in barley

The effect of nitrogen forms on photosynthesis and anti-oxidative systems of barley plants under chromium stress was studied in a hydroponic experiment. The treatments comprised three chromium concentrations (0, 75, and 100 mu M) and three N forms (NH4)(2)SO4, urea, and Ca(NO3)(2). In comparison with the urea or (NH4)(2)SO4 fed plants, the Ca(NO3)(2) fed plants had higher net photosynthetic rate, intercellular CO2 concentration, stomatal conductance, transpiration rate, photosynthetically active radiation utilization efficiency, variable to maximum chlorophyll fluorescence ratio, and the content of chlorophylls and carotenoids. Cr toxicity caused oxidative stress in all plants but the Ca(NO3)(2) fed plants had the least oxidative stress. Moreover, the Ca(NO3)(2) fed plants had higher activities of anti-oxidative enzymes and content of non-enzymatic antioxidants than the urea or (NH4)(2)SO4 fed plants. In addition, the Ca(NO3)(2) fed plants had higher N and lower Cr content in all plant tissues than the urea or (NH4)(2)SO4 fed plants. The current results indicate that the reasonable choice of N fertilizer is important for barley production on the Cr-contaminated soils.