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Aims: Soil organic carbon (SOC) plays an important role in improving soil quality, however, how long-term fertilization influences SOC and contrasting active C (AC) and passive C (PC) pools at large scale remains unclear. The aim of this study was to examine the effect of long-term fertilization on SOC, including AC and PC, across four typical croplands in China and to explore the potential relationships and mechanisms. Methods: We assessed the effect of chemical fertilizer and manure amendment (standard rate and 1.5 × standard rate of inorganic fertilizer (NPK) with or without manure (M), with a Control for comparison) at three soil depths (0–20 cm, 20–40 cm, 40–60 cm) on SOC, AC and PC. Results: We found that SOC, AC and PC increased in the order NPK < NPKM < 1.5NPKM. 1.5NPKM resulting in a significant increase in SOC, AC and PC, of 76.3%, 53.0% and 108.5% respectively across the soil profile (0–60 cm) compared with Control. The response ratio of PC to long-term fertilization was 2.1 times greater than that of AC across four sites on average. In addition, clay was identified as the most important factor in explaining the response of AC and PC to different fertilization application. Conclusions: Long-term fertilization enhanced both AC and PC, but the greater response of PC suggests that fertilization application could enhance the stability of C and thus the potential of cropland for SOC accumulation. [ABSTRACT FROM AUTHOR]

Peatlands are one of the most significant carbon reservoirs in the terrestrial ecosystem. Understanding past peatland carbon accumulation processes and their responses to varying external and internal forcing factors would help reveal the general development patterns of peatland ecosystems and provide useful insights into projecting the fate of carbon reservoirs into the future. In this paper, the basal ages of 17 peat cores were used to explore the lateral expansion processes of the Laolike peatland, northeast China. Two cores were selected to calculate carbon accumulation rates (CAR) and reconstruct moisture/precipitation records based on δ13C and grain size analyses. The basal ages show that the peatland was initiated at 12.1 cal kyr BP, then laterally expanded with its fastest rate occurring during the early Holocene, and reached its largest area around 6 cal kyr BP. The time-weighted mean CAR in the Laolike peatland ranged from 31.1 to 52.9 g C/m2/yr (with an average of 42 g C/m2/yr) during the Holocene. The peatland experienced a high CAR of 52.5 g C/m2/yr from 11.7 to 5 cal kyr BP, followed by a low CAR of 35.1 g C/m2/yr after 5 cal kyr BP. Both lateral expansion and vertical accretion are consistent with the summer insolation, climate seasonality, and the strength of the East Asia summer monsoon (EASM) over multi-millennium timescales, where the CAR correlated well with δ13C and grain size, implying moisture/precipitation might be the primary factors controlling carbon accumulation over millennium timescales. Local conditions, such as topography and hydrology, also played an important role in the process of peatland initiation and lateral expansion, as well as the discrepant CAR within the peatland. This study reveals the roles of climate and local conditions in peatland initiation, expansion, and CAR during the Holocene. In addition, we provide a window for a better understanding of the driving factors of peatland development in the temperate zones of the Northern Hemisphere. • Climate conditions are the primary control on the lateral expansion and vertical accretion of Laolike peatland over multi-millennium timescales. • Moisture/precipitation affects carbon accumulation of Laolike peatland over millennium timescales. • Local conditions play an important role in the lateral expansion and the internal differences of carbon accumulation rate. [ABSTRACT FROM AUTHOR]