Possible Mechanisms Leading to a Delay in Carbon Stock Recovery after Land Use Change

Abstract

Changes in land use sometimes lead to soil C loss, and a long time may be required for the C stock to recover to initial levels. Thus, it is important to evaluate the mechanisms related to accumulation of newly input C following land use changes. In this study, we sought to determine the signature of newly input C in the soil profile after land use change. We used stable and radioactive C isotopes with soil fractionation methods in a C3 coniferous plantation converted from C4 grassland in Japan. The difference in δ13C values between the surface litter and the soil organic carbon (SOC) below the litter was 5‰ or greater; this large isotopic difference was attributed to rapid decomposition in the litter layer and preservation of C derived from the previous C4 vegetation. Most SOC Δ14C values were negative throughout the soil profile, suggesting that most of the SOC in the soil profile was recalcitrant and had been preserved for a long time. Only the surface sand values were slightly positive. These results suggest that most newly input C is consumed at the soil surface. The low ability of these soils to preserve newly input C is one factor in the slow recovery of soil C.

Factors contributing to greater soil organic carbon accumulation after afforestation in a Japanese coniferous plantation as determined by stable and radioactive isotopes

“…The δ 13 C values of the SOC in the C. japonica plantation stand was used as δS, and the reference δ 13 C values for C 3 SOC (δC 3 ) were those observed in the natural forest stand. Due to the lack of reference δ 13 C values for C 4 -derived SOC (δC 4 ) in this study, the δC 4 values were estimated using the δ 13 C value for M. sinensis (−10.9‰; Arai et al, 2007) based on the assumption that the proportional discrimination (D) of M. sinensis during decomposition processes was the same as that of the δ 13 C profiles of the natural forest stand soil (Roscoe et al, 2001):…”

“…Thus, evaluating SOC accumulation mechanisms after afforestation is important. In a previous report, Arai et al (2007) used stable and radiocarbon isotope studies to suggest that the lower C sequestration potential was due to faster decomposition rates in a Cryptomeria japonica stand that replaced a C 4 Miscanthus sinensis grassland. However, the study used soil samples obtained from a single soil profile, although the stand was established at the same time that the atmospheric radiocarbon content began to increase (Manning et al, 1990).…”

“…The present study was conducted using the same C. japonica plantation stand used by Arai et al (2007) and the adjacent natural forest, which was employed as a C 3 reference site. The SOC stock derived from the current C. japonica stand was estimated using the δ 13 C values of the SOC.…”

Soil organic carbon accumulation following afforestation in a Japanese coniferous plantation based on particle-size fractionation and stable isotope analysis

“…The other stand was a 55-year-old C. japonica plantation. Before establishment of the plantation, this site had been used as a common community area for harvesting M. sinensis for roofing materials (Arai et al, 2007). The soils at both sites are characterized as silt loam (Dystrochrept).…”

“…In each fraction, the δ 13 C values of SOC from the C. japonica plantation were used as δS, and the reference δ 13 C values for C 3 SOC (δC 3 ) were those observed in the natural forest stand. The δ 13 C values for C 4 -derived SOC (δC 4 ) were estimated using the δ 13 C value for M. sinensis (−10.9‰; Arai et al, 2007) based on the assumption that the proportional discrimination (D) of M. sinensis during decomposition processes is the same as that of the δ 13 C profiles of natural forest soil (Roscoe et al, 2001):…”