The Use of Natural Abundance of 13CO2 to Determine Soil Respiration Components in An Agro-Ecosystem.

Soil carbon dioxide accounts for 25% of the total annual exchange of carbon between the atmosphere and terrestrial ecosystems. As the atmospheric temperature rises, the microbial activity in the soil increases, resulting in higher respiration rates. Thus, there is growing concern that the sequestering strength of terrestrial ecosystems could be critically affected by changes in soil respiration. Non-steady state flow-through chambers were used in corn fields to quantify the soil respiration and its δ¹³CO₂ isotopic ratio. The objective was to measure total soil respiration and to observe the seasonal and diurnal variations of δ¹³CO₂ emitted from a calcareous soil agro-ecosystem. Small plots with corn (a C4 plant) and without corn plants were established in a large conventionally tilled field derived from limestone bedrock. A bare soil control plot where C4 plants had not been grown in the last 30 years was established nearby. During sampling, chambers were placed on collars and air samples were drawn with a syringe four times at 6 minute intervals. Air samples were analyzed for CO₂ concentration and δ¹³CO₂ value. For further understanding of the effects of carbonates in the soil, soil incubation and the δ¹³CO₂ for carbonates within the soil profile was examined.  The diurnal and seasonal trends of  δ¹³CO₂ observed in the different treatments will be related to potential substrates (roots, soil and carbonates).