Characteristics Of Soil Carbon And Iron Oxide And Their Responses To Moisture Change And Iron Oxide Addition In The Forests Of The South Subtropical In Dinghushan

With global climate change,atmospheric CO₂ concentration continues to rise and regional precipitation will undergo changes.Forest soil carbon is significance for maintaining global carbon balance and climate stability and soil carbon accumulation has been paid more and more attention.There are abundant soil iron oxide contents in the south subtropical forest and the carbon accumulation process may be affected by soil moisture change and iron oxide.Therefore,two forest soils,evergreen broad-leaved forest soil and masson pine forest soil,were studied in Dinghushan National Nature Reserve in the south subtropical region.We measured soil organic carbon components and ferric oxide components in subtropical forests and explored their relationships.After that,in 90 days indoor culture experiment,different soil moisture(30%,60%and 90%water holding capacity,WHC)and add iron oxide treatment groups were set up.This study researched the response of soil carbon mineralization,accumulation and ferric oxide to soil moisture changing and ferric oxide addition.The conclusions are as follows.(1)There is a close relationship between soil carbon and iron oxide in south subtropical forests and soil moisture is an important environmental factor affecting iron oxide.Soil total carbon,total organic carbon and non-oxidized organic carbon were significantly positively correlated with Fe_d,Fe_o and Fe_p,but not with soil total iron.There was a strong positive correlation between ROC and Fe_p.The C/Fe mole ratio is greater than 1 and it indicated that Co-precipitation is the main process of carbon and iron binding in soil.There was a close relationship between soil carbon components and iron oxide components in subtropical forests.Soil water content and water holding capacity were positively correlated with soil total carbon,total organic carbon,NROC,Fe_d,Fe_o and Fe_p and free degree.The results of RDA analysis and SEM path analysis showed that soil water content was an important environmental factor affecting soil iron composition.There is a strong positive correlation between Fe_d and soil water content.(2)The average mineralization rate of soil organic carbon in south subtropical forest under different soil holding water capacity was 60%>90%>30%.The total amount of soil organic carbon mineralization increased with the increase of water holding capacity.After adding iron oxide,the average rate and cumulative amount of soil carbon mineralization in evergreen broad-leaved forest of 60%and 90%WHC groups decreased compared with the control group,while the decrease occurred in 30%and 90%WHC groups of masson pine.Factor variance analysis showed that soil moisture significantly affected the average soil mineralization rate and cumulative soil mineralization.The interaction of forest type,WHC and iron oxide had a significant effect on the cumulative soil organic carbon mineralization.There was a positive correlation between the amount of soil carbon mineralization and Fe_o and Fe_p,while the total soil organic carbon had no obvious response to the change of soil water content and the addition of ferric oxide.(3)After ferric oxide was added,Fe_d increased significantly compared with the control group.The content of Fe_o and Fe_p had no obvious change.The activation degree and complexation degree decreased significantly.Soil iron oxide components in evergreen broad-leaved forest were affected by moisture.Fe_o has the highest sensitivity to WHC change.In the culture experiment,both Fe_d and Fe_o were positively correlated with soil total organic carbon,while Fe_p had no significant correlation with soil total organic carbon.In conclusion,forest soil organic carbon is closely related to iron oxide.The decomposition and accumulation process of soil organic carbon has obvious response to soil moisture change and iron oxide addition.With future climate change,the stability of soil carbon pool in south subtropical forests may change due to the change of iron oxides.Then it affects the carbon cycle of terrestrial forest ecosystems.