| As an important carbon pool in terrestrial ecosystems,peatlands play an important role in the global carbon cycle and have profound impacts on global climate change.The initiation and carbon accumulation processes,rates,and their influencing factors during the Holocene,which is of great significance for revealing the contribution of modern carbon cycle and protecting the ecological function of peatlands,are closely related to the climate change,vegetation dynamics,and regional hydrological pattern.Studies on the initiation and carbon accumulation of peatlands are mainly focus on the northern（middle-high latitudes in the Northern Hemisphere）and tropical peatlands.Changbai Mountains,as a concentrated distribution area of peatlands in China,belongs to the southern extension of northern peatlands in eastern Eurasia.Compared with the northern peatlands,the initiation and carbon accumulation processes and the biodiversity of the peatlands in Changbai Mountains have certain regional characteristics due to the warm climate and abundant precipitation in this area.Previous studies on the initiation and carbon accumulation process of peatlands in Changbai Mountains were mostly based on a single or a few cores,which made it difficult to form a systematic cognition from individual（single peatland）and regional scales.This paper also analysed the effects of climate,vegetation,and topography on the initiation,expansion and carbon accumulation rate of peatlands in Changbai Mountains.The scientific question to be answered in this article are as follows:1)How did the peatland initiate,expand,and carbon accumulate in the Changbai Mountains during the Holocene?2)Does the carbon accumulation process of peatlands at a regional scale have unique characteristics that are compatible with the climate?3)How does climate,species composition,and topography affect the initiation,expansion and carbon accumulation rate?The aims of this study were to:1)Identify the initial age and reconstruct the initiation and expansion process of peatland in Changbai Mountains during the Holocene.2)Discuss the effect of local topography in the lateral expansion of peatland based on the Laolike peatland and Baijianghe peatland.3)Reveal the process of carbon accumulation of peatland in the Changbai Mountains using age-depth models based on the 14 cores obtained from 11 peatlands by measuring bulk density,total organic carbon content,and of carbon calculation accumulation rates of each core.4)Explore the regional characteristics of carbon accumulation of peatlands in Changbai Mountains through correlation analysis among the lateral expansion rate,deposition rate,and carbon accumulation rate of peatlands in the Changbai Mountains.5)Investigate the effects of climate,vegetation,and topography on the initiation and carbon accumulation of peatlands in Changbai Mountains by palaeoclimate reconstruction,macrofossil analysis,and multi-core comprehensive comparison.The main conclusions are as the follows:（1）Most of the peatlands in the Changbai Mountains initiated from middle and late Holocene.For example,the Baijianghe peatland initiated from 7.9 cal.kyr BP,had the highest lateral expansion rate during 5–4 cal.kyr BP and decreased slowly since then.Only a few peatlands initiated in the early Holocene.For example,the Laolike peatland initiated from 12.1 cal.kyr BP and had highest lateral expansion rate during 12–9 cal.kyr BP.（2）Based on the data analysis of 14 peat cores,154 AMS14C dating points and 4552peat samples from 11 peatlands,the general characteristics of peat deposition rates and carbon accumulation rates in Changbai Mountains during the Holocene were obtained.The deposition rates and the carbon accumulation rates ranged from 0.01 to 0.33 cm/yr and 3.9 to198.5 g C/m2/yr,respectively,with average values of 0.08±0.04 cm/yr and 43.4±19 g C/m2/yr,respectively.The carbon accumulation rates in Changbai Mountains were highest during the period from 12 to 9 cal.kyr BP and decreased between 9 and 3 cal.kyr BP but increased since then.（3）Climate was the main factor influencing the initiation,expansion,and carbon accumulation rate of peatlands in Changbai Mountains.The high summer insolation,great climate seasonality,and strong East Asian summer monsoon during the early Holocene in the Northern Hemisphere resulted in the deeper surface water in the low-lying areas of the Changbai Mountains and were not conducive to the initiation and expansion of peatlands.However,such climatic conditions were benefiting for the extension of the growth season,the improvement of net primary productivity and the highest rate of carbon accumulation.The initiation frequency of peatlands increased but the rate of carbon accumulation decreased due to the shortened growth season and reduced net primary productivity caused by the weakening of solar insolation,the reduction of climate seasonality,and the weaken of the East Asian summer monsoon during the middle Holocene in the Northern Hemisphere.During the late Holocene,there were weakest summer solar insolation,climate seasonality,and the East Asian summer monsoon intensity,which reduced the water table in the low-lying areas of Changbai Mountains,induced peatland’s initiation and expansion at large-scale.The increasing carbon accumulation rate mainly attributed to the low degree of decomposition of the newly formed peat.The relationship between paleoclimate reconstruction and carbon accumulation rate based onδ13C,δ18O,and grain size in the Laolike peatland showed that carbon accumulation rates were highest under wettest condition between 12 to 9 cal.kyr BP and were lowest under driest and coldest condition during the last3 cal.kyr BP.（4）The relationship between lateral expansion rate and deposition rate varied among different peatlands in Changbai Mountains based on the correlation analysis among the lateral expansion rate,deposition rate,and carbon accumulation rate.The peat deposition rates were different among different peatlands with similar expansion processes.In addition,the carbon accumulation rate varied among different peat cores at the local scale.Local factors such as species composition and topography could play important roles in determining the carbon accumulation rate in Changbai Mountains.（5）The effect of species composition on the carbon accumulation rates varied among different peatlands in Changbai Mountains.The carbon accumulation rate was high when the vegetation dominated by herbaceous in Laolike peatland,but low when the dominated by Sphagnum spp.increased.The deposition rate and carbon accumulation rate were low when the vegetation dominated by woody plants in Baijianghe peatland.However,the correlation analysis between Sphagnum spp.and carbon accumulation rate varied among different cores with positive correlation or negative correlation.（6）The comprehensive comparative analysis of multiple-core in the Laolike and Baijianghe peatland indicated that topography was the main reason for the heterogeneity of the carbon accumulation rate at local scale in Changbai Mountains The accumulation rate in peatlands had great spatial differences during the early stage of carbon accumulation due to differences in local topography,hydrology,and their effects on the redistribution of climate factors such as temperature and precipitation.During the late stage of carbon accumulation,the influence of topography and hydrology gradually weakened,and climatic conditions became the main influencing factors of carbon accumulation in peatlands.Therefore,with the increase of peat thickness,the rate of carbon accumulation showed consistent changes during the late stage of carbon accumulation.Based on the reconstruction of initiation,expansion,and carbon accumulation of peatlands in Changbai Mountains,this paper revealed and discussed the characteristics,rules,and influencing factors of initiation,expansion and carbon accumulation rates of peatlands at different spatial scales.Our results were not only conducive to the deep understanding of the laws and potential mechanisms of peatland initiation,expansion,and carbon accumulation in the mid-latitudes of the northern hemisphere,but also provide scientific basis and great data support for further assessing the carbon sequestration capacity of peatlands in Changbai Mountains and formulating regional carbon neutralization programs,respectively. |
