Contribution of soil organic carbon and C<sub>3</sub> sugar to the total CO<sub>2</sub> efflux using <sup>13</sup>C abundance

Abstract

The differences in C isotope ratio of C<sub>3</sub> and C<sub>4</sub> plant species have been used to determine relative contributions of carbon (C) sources to total CO<sub>2</sub> efflux. The objective of this study was to estimate the contribution of soil organic C and C<sub>3</sub> sugar to total CO<sub>2</sub> of corn and wheat monocultures during a short-term incubation. Control soils and soils amended with sugar were incubated at 25°C for 48 hours and total CO<sub>2</sub> concentration and δ<sup>13</sup>C values of evolved CO<sub>2</sub> were measured. The proportional contribution of C sources on CO<sub>2</sub> efflux was determined by using isotopic composition of soil organic C and C<sub>3</sub> sugar. δ<sup>13</sup>C values of soils are highly affected by the type of vegetation and the soil management. The C<sub>3</sub> sugar addition in soils double the CO<sub>2</sub> efflux in the corn soil, but it did not affect CO<sub>2</sub> efflux in the wheat soil. This indicated a larger turnover of microbial biomass in the corn soil. The greatest significant (P < 0.05) difference in δ<sup>13</sup>C values between the control and sugar added soils occurred at 12 hours in the corn soil (11.2‰) and at 24 hours in the wheat soil (9.4‰). The estimated relative contribution of sugar to CO<sub>2</sub>efflux was stronger at 12 hours incubation in the corn soil.