Fig. 2

Expression levels of the AMT1;1, AMT1;3, gdh2, and gdh3 genes in the very fine roots and fine roots of Gossypium hirsutum in the different treatments. Fine roots are those with diameter between 0.1 and 2 mm, while very fine roots are those with diameter less than 0.1 mm. The treatments include ck (control), sb (conventional 3.76 g urea kg⁻¹ soil applied in the 0–10 cm soil layer), bb (conventional 3.76 g urea kg⁻¹ soil applied in the 10–20 cm soil layer), soa (urea was reduced by 25% on the basis of sb plus 37.28 g biochar kg⁻¹ soil), sob (urea was reduced by 50% on the basis of sb plus 37.28 g biochar kg⁻¹ soil), boa (urea was reduced by 25% on the basis of bb plus 37.28 g biochar kg⁻¹ soil), and bob (urea was reduced by 50% on the basis of bb plus 37.28 g biochar kg⁻¹ soil). The last letters f and m of each treatment indicate very fine root and fine root, respectively. Results are presented as mean values for five plants with SE. Asterisk indicates significant difference with a confidence interval at *P < 0.05 or **P < 0.01