CO2 production in anthropogenic Chinampas soils in Mexico City .


We studied microbial-associated CО2 production in anthropogenic chinampas soils. The soils were constructed by the accumulation of materials such as organic matter and loamy lacustrine sediments in Pre-Hispanic cultures in Mexico. To study the temperature sensitivity of CО2 production related to soil depth, moisture and oxygen availability, soil samples were collected at depths of 0-7, 7-18, 18-30, 30-40 and 40-50 cm. The soil samples were incubated under aerobic and anaerobic conditions at controlled temperatures (-5, 0, 5, 10, 20, 30 °C) and soil moistures of 10, 30, 60 and 90% water-filled pore space. For all the soil depths, incubation temperatures and soil moistures, the mean rate of aerobic CO2 production was 58.0 mg CO2 kg-1 d-1 and that of anaerobic CO2 production 31.2 mg CO2 kg-1 d-1, with the highest rate found in the soil samples collected at a depth of 0-7 cm. A decrease in soil organic carbon content inhibited CO2 production more under anaerobic than aerobic conditions. The dependence of aerobic СО2 production on soil moisture increased at what constituted both unusually high and low temperatures for the study area. Since the response of СО2 production to temperature was lower under anaerobic than aerobic conditions, the increase in soil moisture content led to a decrease in the temperature sensitivity of СО2 production. The response of microbial activity to other factors may be modified under what constitutes the limiting conditions for any of the factors considered, as follows: (i) when anaerobiosis increases in the soil, the limiting effect of substrate availability on microbial activity increases; (ii) the CO2 production rate becomes more dependent on soil moisture under temperature stress; (iii) the sensitivity of CO2 production to temperature is highest under drought stress.
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