Abstract
We studied microbial-associated CО<sub>2</sub> production in anthropogenic <em>chinampas</em> 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 CО<sub>2</sub> 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 CO<sub>2</sub> production was 58.0 mg CO<sub>2</sub> kg<sup>-1</sup> d<sup>-1</sup> and that of anaerobic CO<sub>2</sub> production 31.2 mg CO<sub>2</sub> kg<sup>-1</sup> d<sup>-1</sup>, 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 CO<sub>2</sub> production more under anaerobic than aerobic conditions. The dependence of aerobic СО<sub>2</sub> production on soil moisture increased at what constituted both unusually high and low temperatures for the study area. Since the response of СО<sub>2</sub> 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 СО<sub>2</sub> 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 CO<sub>2</sub> production rate becomes more dependent on soil moisture under temperature stress; (iii) the sensitivity of CO<sub>2</sub> production to temperature is highest under drought stress.
Highlights
There are large spatial and temporal variabilities in the rates of soil CO2 production, caused by a wide range of environmental biotic and abiotic factors and the great diversity of soil types (Baggs 2006; Lee et al 2006)
The fields were created by the accumulation of materials such as organic matter and loamy lacustrine sediments which were consolidated into islands separated by a system of channels. (Jiménez-Osornio and GomesPompa 1987; Ramos-Bello et al 2011)
Root density, texture and compaction allowed for division of the 50 cm topsoil into four layers. We designated these layers as A1, A2, A3 and A4, with A denoting superficial humus-enriched horizon and the numbers indicating sub-horizons which were distinguished by the layered morphology of the horizon. This layered morphology is typical for chinampas soils and it is believed to be the result of anthropogenic accumulation of excavated lacustrine sediments on the surface rather than of pedogenetic processes
Summary
There are large spatial and temporal variabilities in the rates of soil CO2 production, caused by a wide range of environmental biotic and abiotic factors and the great diversity of soil types (Baggs 2006; Lee et al 2006). The existing data show that CO2 emissions strongly depend on the taxonomic soil group, with studies covering almost all the groups of mineral and organic soils in the world (Batjes 2006). For some endemic soil groups such as anthropogenic agricultural soils the data on CO2 production are still insufficient. One inadequately studied soil is the anthropogenic chinampas soil of Mexico City. Pre-Hispanic cultures in Mexico developed a specific technology for cultivating wetlands around the lakes in the Valley of Mexico. They constructed elevated fields for agricultural production (Ezcurra 1990) called “chinampas” (a word of Nahuatl origin: chinamitl – “straw bed”, and pan – “over”). The fields were created by the accumulation of materials such as organic matter and loamy lacustrine sediments which were consolidated into islands separated by a system of channels. (Jiménez-Osornio and GomesPompa 1987; Ramos-Bello et al 2011)
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