Effect of nitrogen fertilization on nitrogen metabolism of Festuca arundinacea under heat stress

The effects of different nitrogen treatments (NO3-, NH4+ and NH4NO3) on the contents of nitrate and ammonium nitrogen, as well as the activity of main enzymes involving in the process of assimilation and metabolism in leaf of Festuca arundinacea under high temperature (38/30 ℃,day/night) were studied by plot experiment. The results indicated that the nitrate content increased at the beginning and then declined along with the stress treatment time, however, the ammonium nitrogen content showed an increasing trend. The nitrate content was the highest and the lowest was ammonium nitrogen content in the leaf treated by NH4NO3. The ammonium nitrogen content was the highest in the leaf treated by NH4+. The activity of nitrate reductase (NR) showed a decline trend under different treatments. The activity of glutamine synthetase (GS) and glutamate synthase (GOGAT) increased at the beginning and then decreased. In general, the activity of NR, GS and GOGAT in leaf treated by NH4NO3 was the highest. Activity of glutamate dehydrogenase (GDH) in leaf treated by NH4NO3 and NO3- showed a decline trend, and that of GDH treated by NH4+ showed an increasing trend. It could be concluded that the oxidative stress on F. arundinacea treated by NH4NO3 was the smallest and its heat tolerance was the best.