Abstract: A pool-culture experiment was conducted to study the effects of different subsoil bulk density at the depths of 20-40 and 40-60 cm on the late growth stage photosynthetic characteristics and grain yield of maize. The results showed that there existed significant differences in the net photosynthetic rate (P_n) and grain yield when the subsoil bulk density was differed. The P_n and grain yield decreased with increasing subsoil bulk density, and the higher the bulk density, the more significant the decrement inP_n and grain yield. The diurnal changes of P_n and intercellular CO₂ concentration (C_i) were not in the same trend. P_n was high at noon and low at twilight and dusk, and decreased with increasing subsoil bulk density; while C_i was in adverse. The stomatal limitation (L_s) and stomatal conductance (G_s) also decreased with increasing subsoil bulk density. With the development of maize, the P_n,L_s and G_s decreased gradually, while C_i increased continuously.

Key words: fire fighting, fire prevention by using fire, fuel management, forest fire policy, forest fire in the United States