Aggregational differentiation of soil-respired CO2 and its δ13C variation across land-use types

Land-use type can affect CO2 emission fluxes, but whether it has effects on the delta C-13 of respired CO2 (delta(CO2)-C-13), and whether these effects vary with the heterogeneity of the soil microenvironment remain unknown. In this study, long-term soil incubation experiments and soil fractionation were combined to determine the effects of land-use type (upland, paddy and woodland) on soil-respired CO2 and delta(CO2)-C-13 with different aggregate fractions under three temperature conditions. This study extended the thermal adaptation of soil respiration to the soil microenvironmental scale, i.e., the scale of smaller aggregates than bulk soil. An exponential decay function (R = a x e(-b)t) was fitted to the temporal soil respiration data, separately for each combination of soil aggregate, land-use type and incubation temperature. At each incubation stage, the woodland exhibited the highest average soil respiration rates. The exponential decay trend of delta(CO2)-C-13 with time was influenced by the land-use type and incubation temperature; the shift from enriched to depleted delta(CO2)-C-13 values first appeared in woodland. Interestingly, carbon isotopic discrimination between the substrate and respired CO2 (Delta C-13, delta(CO2)-C-13 - delta C-13(SOC)) increased with aggregate size only in woodland, especially at 30 degrees C. Overall, aggregational differentiation of soil-respired CO2 and its delta C-13 was found only in the woodland, and warming intensified these differences, suggesting that it would be difficult to generalize the integrative effects of warming on soil respiration and its isotopic fractionation at the microscale from a single ecosystem study. Our findings highlight that land-use types affect the feedback of soil carbon pool to future global warming at the soil microenvironmental scale (aggregate), and are of great significance for improving carbon emission prediction in terrestrial ecosystems.

Automated summary

Land-use type influences CO2 emission fluxes, delta(CO2)-C-13, and the effects of heterogeneity in soil microenvironment. This study investigated the effects of land-use type on soil-respired CO2 and delta(CO2)-C-13 using long-term soil incubation and fractionation techniques. Results showed that woodland had the highest soil respiration rates and exhibited a shift in delta(CO2)-C-13 values. Aggregational differentiation of soil-respired CO2 and delta C-13 was found only in the woodland, and warming intensified these differences. These findings are important for understanding the feedback of soil carbon pool to global warming.