Climate Evolution Recorded by Organic Carbon Stable I sotope since 5 kaB.P.in Poyang Lake Area, China

Based on the data of organic carbon stable isotope ratios and magnet ic susceptibility, climate evolution in the past 5 kaB.P. in Poyang Lake plain (in Jiangxi Province) has been reconstructed. The results of the research indicate that the climate evolution can be divided into nine stages in the past 5 kaB.P.. Comparisons of different regional environmental records suggest that the intens ity and the temporal spatial changes of monsoon in China mainly controlled the climate evolution.

Effects of precipitation on soil organic carbon fractions in three subtropical forests in southern China

Aims The aim of this study was to investigate the effects of precipitation changes on soil organic carbon(SOC)fractions in subtropical forests where the precipitation pattern has been altered for decades.Methods We conducted field manipulations of precipitation,including ambient precipitation as a control(CK),double precipitation(DP)and no precipitation(NP),for 3 years in three forests with different stand ages(broadleaf forest[BF],mixed forest[MF]and pine forest[PF])in subtropical China.At the end of the experiment,soil samples were collected to assay SOC content,readily oxidizable organic carbon(ROC)and non-readily oxidizable organic carbon(NROC),as well as soil microbial biomass carbon(MBC),pH and total nitrogen content.Samples from the forest floors were also collected to analyze carbon(C)functional groups(i.e.alkyl C,aromatic C,O-alkyl C and carbonyl C).Furthermore,fine root biomass was measured periodically throughout the experiment.Important Findings Among the forests,ROC content did not exhibit any notable differences,while NROC content increased significantly with the stand age.This finding implied that the SOC accumulation observed in these forests resulted from the accumulation of NROC in the soil,a mechanism for SOC accumulation in the mature forests of southern China.Moreover,NP treatment led to significant reductions in both ROC and NROC content and therefore reduced the total SOC content in all of the studied forests.Such decreases may be due to the lower plant-derived C inputs(C quantity)and to the changes in SOC components(C quality)indicated by C functional groups analyses under NP treatment.DP treatment in all the forests also tended to decrease the SOC content,although the decreases were not statistically significant with the exception of SOC and ROC content in PF.This finding indicated that soils in MF and in BF may be more resistant to precipitation increases,possibly due to less water limitations under natural conditions in the two forests.Our results therefore highlight the different responses of SOC and its fractions to precipitation changes among the forests and suggest that further studies are needed to improve our understanding of SOC dynamics in such an important C sink region.

Soil organic carbon saturation deficit under primary agricultural managements across major croplands in China

Introduction:To generate information for the effective management of soil organic carbon(SOC)sequestration in Chinese croplands,we compared the additional organic carbon(C)that can be stabilized by fine soil particles(<20μm)with typical fertilization practices across soil types and climate zones.Using data from 30 long-term experimental study sites across the major agricultural zones in China,we estimated stable SOC saturation deficit(SOC_(deficit))under no fertilization(CK),chemical fertilization(CF),straw plus CF(S+CF),and manure plus CF(M+CF).Stable SOC_(deficit)was defined as the difference between potential and current SOC stabilized by fine soil particles.Outcomes:Stable SOC_(deficit)values varied from 51%to 82%.Soils dominated by 2:1 clay minerals showed larger stable SOC_(deficit)than soils dominated by 1:1 clay minerals under each treatment.For soils dominated by 2:1 clay minerals,stable SOC_(deficit)was significantly lower under M+CF(69%)than under CK,CF,and S+CF(78-82%)treatments,and it increased with increasing mean annual temperature(<10°C).In soils dominated by 1:1 clay minerals,stable SOC_(deficit)was considerably lower in paddy and paddy-upland than in upland soils,suggesting that paddies effectively stabilize C inputs.Discussion:Agricultural soils in China have considerable C sequestration potential,despite decades of fertilization practices.To manage soil C sequestration and model soil C dynamics effectively,factors such as soil mineral types,fertilization,and cropland use should be considered.Conclusion:Our results demonstrated that manure addition was the best fertilization method for improving soil fertility,whereas straw return in Chinese croplands should take into account climate mitigation in future.

Variations in paleoproductivity and the environmental implications over the past six decades in the Changjiang Estuary

Total organic carbon and organic carbon stable isotope, biogenic silica, chlorin were measured from a high resolution sediment core to indicate the variation in paleoproductivity and the environmental implications over the past decades （1942 to 1997） in the Changjiang Estuary. Based on these biomarkers, the shift in the phytoplankton community structure in the past decades was discussed in response to the long-term variations in nutrient concentrations and nutrient ratios. The results showed that the δ 13 C values varied from –26.15‰ to –19.5‰, suggesting the combined organic carbon sources of riverine and marine organisms. Based on the biogenic proxies, paleoproductivity changes were categorized into three stages： low production before 1950; an increase in production with the dominance of diatoms during 1950 to 1980, consistent with increasing of nutrient concentrations; a decrease in production after 1980 when the diatom production decreased while the production of non-silicious phytoplankton increased due to high nutrient inputs, and high N/P and P/Si ratios in the Changjiang Estuary. The sedimentation records also indicated that the riverine organic carbon increased since 1980.