Effect of elevated CO_2 and temperature on microbial biomass nitrogen and nitrogen mineralization in submerged soil microcosms

抄録

A forty-five day incubation experiment was conducted under controlled laboratory conditions to study the interactive effects of elevated CO_2 concentration and temperature on the changes of the amount of microbial biomass nitrogen (N) and the mineralization of N in flooded paddy soil microcosms amended or not with rice straw. The microcosms with the two treatments were transferred separately to four growth chambers under different conditions of incubation and a 16 h/8 h light and dark regime. Two of the growth chambers provided a continuous flow of elevated CO_2 concentration (equivalent to 800 μl 1^<-1>), of which one was set at 25 ℃ and the other at 35 ℃. Similarly the other two growth chambers were run under near ambient CO_2 concentration (400 μl 1^<-1>) at each of the two temperatures. Replicates of microcosms were withdrawn from each of the growth chambers after 7, 15, 30 and 45 days of incubation and analysed for the contents of extractable N (E_n), microbial biomass N, ammonia and total N in surface (0-1 cm) and sub-surface (below 1 cm) soil layers. There was a significant difference between the amounts of E_n in the surface layers and sub-surface layers under all the conditions, the levels in the sub-surface soils being higher than those in the surface soils. The amount of microbial biomass N and total N content increased under elevated CO_2 concentration at the end of incubation compared with the ambient CO_2 concentration. The increase in total N content implied that the potential of biological N_2-fixation increased by elevated CO_2 concentration. N mineralization was enhanced by both elevated atmospheric CO_2 concentration and temperature in submerged rice soil without plants.