Effect of Inorganic Nitrogen Forms on Growth and Kinetics of Ammonium and Nitrate Uptake in Camellia sinensis L.
The ammonium and nitrate nitrogen are the main inorganic nitrogen in crop cultivation, the rational application of chemical N fertilizer and improvement of N use efficiency in tea plant are important for tea cultivation. There was little research on the relationship between inorganic nitrogen form and root absorption properties of perennial woody plants. In this study, four tea plant cultivars (Wuniuzao, Longjing 43, Yingshuang, and Zhenong 139) were selected for a pot experiment, and the influences of different N fertilizers with different ratio of NO_3~--N : NH_4~+-N on height growth and girth growth of tea were studied. In order to explore the absorption mechanism of different inorganic N forms, Michaelis-Menten equations of different N forms were estab-lished and compared. The results showed that the chemical nitrogen form of the fertilizer had a very significant effect on the height growth of the tea, but no significant effect on girth growth. The tea height significantly increased, and the increasing amount reached 15.45 cm per year at 5:5 of NO_3~--N : NH_4~+-N ratio, while at the pure NH_4~+-N treatment, the increasing amount was only 7.03. Compared with other tea cultivars, the increasing amount in height of Wuniuzao was the most, and in girth of Longjing 43 was the least. The maximum uptake rate (V_(max)) for nitrate nitrogen (NO_3~--N) absorption decreased when the propor-tion of ammonium nitrogen (NH_4~+-N) increased. The affinity to NO_3~--N was enhanced gradually, but weakened when the propor-tion of NH_4~+-N was over 50%. The V_(max) for NH_4~+-N absorption increased quickly until the proportion of NH_4~+-N was over 50%, and then decreased slowly. The affinity to NH_4~+-N weakened slowly until the NH_4~+-N proportion was over 50%, and quickly when the ammonium proportion was too high. When the NO_3~-: NH_4~+ was 5:5, the V_(max) values for NO_3~--N and NH_4~+-N were 0.24-0.35 and 0.19-0.30 mmol FW g~(-1) d~(-1), respectively, and the K_m values were 0.65-0.74 and 0.63-0.80 mmol L~(-1), respectively, indicating that the nitrogen absorbing status was better than that of other treatments. In the pot experiment, nitrogen forms had a great effect on the nitrogen absorption kinetics, indicating the tea tree had an adaptation mechanism to the change of N fertilizer.
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