耕作及水蚀影响下坡耕地土壤有机碳动态模拟

土壤侵蚀和沉积明显影响土壤有机碳(SOC)的积累与损耗,在以往土壤碳平衡模拟中却未得到应有的重视。本文以典型黑土漫岗坡耕地表层土壤为研究对象,利用CENTURY模型模拟特定质地下自然黑土有机碳的积累过程,估算研究区黑土有机碳及各组分的背景值;对比研究侵蚀泥沙对SOC富集的影响,将模型模拟值与实测值进行统计比较来验证模型;进而模拟侵蚀区开垦后SOC以及各组分随时间的变化,定量研究土壤侵蚀对SOC各组分损失的贡献。研究结果表明:黑土有机碳的累积大致可分为初期的快速积累和后期缓慢积累两个阶段,前期慢性有机碳库的累积对SOC库的增加贡献最大,后期SOC累积主要由惰性有机碳缓慢累积来完成。达到平衡状态时,研究区黑土有机碳含量为7 240 g m-2,以慢性和惰性有机碳为主,约占总SOC的97.4%。考虑泥沙对SOC的富集作用,模型模拟值与实测值更加吻合。自然黑土开垦后,微生物分解矿化作用是活性和慢性有机碳损失的主要途径,土壤侵蚀明显降低惰性有机碳含量,其贡献率随侵蚀速率的增加而增大。因研究区侵蚀不严重,土壤侵蚀对开垦以来的SOC库损耗贡献较小。

SIMULATION ON DYNAMICS OF SOIL ORGANIC CARBON UNDER THE EFFECT OF TILLAGE AND WATER EROSION

Soil erosion and deposition influences accumulation and loss of soil organic carbon(SOC),yet it has never been an issue of proper attention in the study of soil carbon cycle.In this paper,the CENTURY model was used to simulate original organic carbon accumulation in black soil of a given soil texture in a typical rolling farmland in the Black soil region,Northeast China to get the initial value of SOC and its fractions;Then the model was verified through statistical comparison between the simulations and actual measurements with and without considering SOC enrichment with sediments;And then temporal variation of SOC and its fractions after reclamation,and contribution of soil erosion to SOC loss were assessed.The results show that SOC accumulation could be divided into two stages,i.e.fast accumulation in earlier stage and slow accumulation in later stage.The slow organic carbon accumulation in the former stage contributed the most to the SOC pool and passive organic carbon played a dominant role in SOC accumulation at the latter stage.When equilibrium was reached the content of organic carbon in the black soil in the study area was 7 240 g m~(-2),of which slow and passive organic carbon accounted for 97.4%;The simulations tallied better with the actual measurements was better when the effect of sediments on SOC enrichment was taken into account;When natural black soil was cultivated,active and slow carbon was most likely to get decomposed by microorganism and mineralized,while passive carbon was losing with soil erosion.It was not so significant because soil erosion was not serious problem in the study area.