Extended Data Fig. 4: Geographical distribution of the sites (a) and sampling strategy (b) in the incubation experiment.

Samples were taken from 39 paddy soil sites located in 13 regions of China. The numbers in parentheses represent the mean annual air temperature (°C) in the sampling region. At each site, 11 nested samples were collected at distances of 1, 6, 16, 36 and 76 m. CC = Changchun; CT = Changting; FQ = Fengqiu; HK = Haikou; HL = Hailun; HY = Hengyang; JO = Jian’ou; LA = Lin’an; OM = organic matter; QX = Qingxin; QZ = Quzhou; SY = Shenyang; TN = total nitrogen; YY = Yuanyang; ZX = Zixi.