Changes in soil microbial biomass C, ATP and microbial ATP concentrations due to increasing soil Cd levels in Chinese paddy soils growing rice (Oryza sativa)

Aims: The mean biomass ATP concentration in aerobic soils is around 10–11 μmol ATP g‾ ¹ biomass C, within a fairly narrow range. It is much lower in short-term incubated laboratory waterlogged soils. However, the biomass ATP concentration in waterlogged paddy soils under field conditions remains unknown. This is investigated. Methods: Soil microbial biomass C (biomass C), ATP, biomass ATP and heavy metal (Cd, Zn, and Cu) concentrations in soil and rice were measured in a Chinese paddy soil growing rice. Soils and plants were analyzed at day 0, 30, 75 and 90, over the 90 day growing period with inputs of inorganic fertilizer, or biochar and manure singly or in combination. Results: Both biomass C and ATP concentrations increased, range from 14.9–30.5% for microbial biomass C and 115.8–160.1% for ATP, from initial values until the end of the experiment following manure or biochar addition. An important result was that the biomass ATP concentration increased throughout the growth period. There were also significant negative correlations (p < 0.05) between total and available Cd and these three microbial parameters, despite the low levels of Cd. Over the same period, total plant Cd concentrations increased, and soil Cd decreased. This suggests that the rice acted as a bioaccumulator. The microbial biomass was then in a continually decreasingly toxic environment and responded rapidly by increasing its size. Conclusions: These results demonstrate clear differences in microbial energy dynamics between aerobic and anaerobic microbial populations. Both ATP and biomass C are useful bioindicators of the effects of cadmium contamination on microbial processes in waterlogged soil