Fig. 1. Stoichiometric and homeostatic characteristics of rice soil under different treatments of biochar-based fertilizer (BBF). A and B, Stoichiometric characteristics in rice variety Nanjing 5055 (A) and under different soil layers (B) under different BBF treatments (CK, CF, M0C0, M1C1, M2C2, and M3C3). Different lowercase letters above bars indicate significant differences (P < 0.05) as determined by Tukey’s honestly significant difference (HSD) test following an analysis of variance (ANOVA). C, Fitting curves examining the relationships between total carbon, nitrogen, and phosphorus contents in rice stems and leaves, and their respective contents in topsoil and subsurface soil. Scatter points represent observed data. The solid curve is a power-function fit, with dashed lines indicating the upper and lower bounds of the confidence interval. D, Stoichiometric homeostasis index (1/H) between rice organs and soil (0-20 cm layer). Plant refers to the above-ground portion of the rice (including stems, leaves, and other organs). E and F, Principal component analysis of soil fertility to 0-10 cm (E, topsoil) and 10-20 cm (F, subsurface soil) soil layers. CK, Control check (conventional fertilization); CF, Conventional fertilization added straw charcoal; M0C0, BBF with 0% straw charcoal; M1C1, BBF with 5% straw charcoal; M2C2, BBF with 15% straw charcoal; M3C3, BBF with 25% straw charcoal; C, Carbon; N, Nitrogen; P, Phosphorus; TC, Total carbon content; TN, Total nitrogen content; TP, Total phosphorus content; BOD, Biochemical oxygen demand; AP, Available phosphorus; AK, Available potassium; OM, Organic matter; PC, Principal component.