N source affects freeze tolerance in bermudagrass and zoysiagrass

During cold acclimation, warm-season grasses exhibit growth stall and eventually the onset of rest. Late-season N fertilization is an alternative way for reduction of the dormancy period. The objectives of the present study were (1) to assess the effects of different N sources, and timing on freezing tolerance using controlled environment acclimation and freezing procedures and (2) to determine the relationship of nonstructural carbohydrates and photosynthetic pigments with the freeze tolerance of bermudagrass and zoysiagrass. NH+ 4 source treatment exhibited a relative peak at 14 days (2 weeks) before the NO- 3 treatment. In bermudagrass, NH+ 4 treatment depressed starch accumulation at 14 and 28 days compared to the control. As expected, in both species a higher concentration of soluble carbohydrates were observed in sprigs tissues. A sharp decline was evident on the NH+ 4 treatment in leaves, stems, and roots tissues at 14 days, in correspondence with a lower freeze tolerance, whereas in the treatment an accumulation in total soluble sugars was observed in rhizomes at 28 days. Over the time, chlorophylls showed a slight increase in the NH+ 4 treatment, while an opposite trend was detected in the NO- 3 treatment. Overall, N source provided consistent differences in freeze tolerance in both species. © 2013 Copyright Taylor and Francis Group, LLC.