Soil Respiration And Soil Carbon Storage Of A Secondary Forest Chronosequense In The In Maoershan Region,Northeast China

Soil respiration?R_S?and belowground carbon storage are the two important roles in both local and national carbon budgets.The spatial and temporal changes in soil surface CO₂ flux,the major CO₂ source to the atmosphere from terrestrial ecosystems,directly influence the local and regional carbon budgets.Soil organic carbon,is the largest carbon storage pool of forest ecosystems in high latitude regions,play a key important on component of ecosystem carbon budgets.Soil respiration?R_S?is the major source of CO₂ efflux to the atmosphere from forest ecosystems.It plays an important role in the carbon balance of the ecosystem.The temperate forests in Northeast China are a mosaic of different aged secondary stands resulting from various logging disturbances.The objective of the present study was to examine variations in R_S and its driving factors as the forests recovered from clear cutting with a chronosequence approach.The chronosequence that included stands of four ages?i.e.,1,10,25,and 56 years since logging?was established in 2014 in the Maoershan region,Northeast China?45°24?N,127°40?E?.The R_S was measured with a LI-840 CO₂/H₂O analyzer from April 2014 to March 2015;and the soil temperature and water content at a depth of 5cm were measured simultaneously.Soil organic carbon?SOC?and fine root?diameter<0.5mm?biomass were also measured at the end of the growing season.The results showed that:?1?the annual R_S differed significantly among the stands?P<0.05?,and averaged 686.5,639.7,733.3,and 762.3g C·m^–2·a^–1 for the 1-,10-,25-,and 56-year old stands,respectively.The R_S in the growing and non-growing seasons differed significantly among the stands.It showed a decreasing trend immediately after the clear cutting,and subsequently increased with increasing stand age.The coefficients of variation in R_S among the stands were 7.6,6.3,and 21.1%for the whole year,growing season,and non-growing season,respectively,suggesting that the variability in annual R_S among stands increased with increase in the non-growing season.?2?The R_S of all the stands followed a similar seasonal trend,but the controlling factors varied with seasons.The R_S between June and August was significantly related with soil water content in a polynomial function?R²=56-79%?,whereas the R_S during the subsequent months was significantly related with soil temperature in an exponential function?R²=85-93%?.?3?The R_S in the growing season was positively correlated with SOC content at a depth of 0-20cm in all the stands?R²=0.434,P<0.05?,whereas that in the non-growing season was correlated positively with soil temperature at a depth of 5cm in the same season?R²=0.959,P<0.01?.These results suggest that the R_S in these forests decrease after logging disturbance and increase with increasing stand age,driven mainly by the increased SOC content and changes in soil temperature during the non-growing season.Total soil organic carbon?SOC?density at 0⁴0 cm differed significantly among the stands?P<0.05?,and averaged 7.68,8.53,8.52,and 8.77 kg/m² for the 1-,10-,25-,and 56-year old stands,respectively.The total SOC density in the 1-year old stand lower than the other aged stands significantly?P<0.05?,and the other aged stands beside 1-year old stand did not differ from each other significantly?P>0.05?.The SCO density at 0⁴0 cm increased subsequently with increasing the stand age.The result suggest that the scores for soil carbon sequestration increased along with the stand age.Our results also showed that the contents of soil organic carbon density decreased with the increased of soil depth.