Effects of Mg and N supply on the content of Mg, amino acids, and GS activity in tea plants grown under the field experiment. A) Mg content in the soil of tea plantation. B) Mg content in mature tea leaves. C) Content of total free amino acids in tea leaves. D) GS activity in tea leaves. N300 and N500 represent that the levels of nitrogen fertilizers are provided as 300 kg/ha and 500 kg/ha urea, respectively. −Mg, Mg20, and Mg50 represent that soil Mg fertilizer levels are 0, 20 kg/ha, and 50 kg/ha, respectively. Error bars show the mean values ± SD (n = 4). Statistical analysis was carried out with Duncan's multiple range test.