我国东北土壤有机碳、无机碳含量与土壤理化性质的相关性

根据黑龙江、吉林、辽宁省和内蒙古地区相关历史资料数据,分析了我国东北表层土壤(0-50 cm)土壤相关理化性质与有机碳、无机碳的相关性,得到如下结论:土壤全氮、碱解氮、全磷、速效磷、速效钾、K⁺离子交换量、Fe₂O₃、P₂O₅、总孔隙度均与土壤有机碳含量呈显著正相关(R²=0.10-0.94, n=38-345, P<0.0001),但与土壤无机碳含量则大多呈显著负相关(R²=0.11-0.30, n=37-122, P<0.01);与此相反,土壤pH值、容重与土壤有机碳呈负相关(R²=0.36-0.42,n=41-304, P<0.0001),而与无机碳呈显著正相关(R²=0.29-0.31,n=39-125, P <0.01)。表层土壤有机碳、无机碳与土壤理化性质呈相反变化趋势的结果说明,由于土壤利用方式变化所导致的土壤理化性质改变对土壤无机碳和有机碳可能具有相反影响。在研究土壤碳平衡过程中,应该充分考虑这种关系所导致的相互补偿作用,即有机碳的增加,可能意味着无机碳的减少,或者反之。目前研究中普遍忽略无机碳的变化,可能导致生态系统碳收支计算显著偏差,所获得的经验拟合方程有利于对我国东北地区土壤碳平衡研究产生的这种偏差进行粗略估计。

Soil organic and inorganic carbon contents in relation to soil physicochemical properties in northeastern China

Soil carbon includes two components of organic carbon(SOC) and inorganic carbon (SIC) and, the amount of SIC in the earth surface is about half of the SOC amount (1500Pg), showing its critical importance in global carbon balance although more studies are on SOC dynamics compared to SIC. Concurrent study on SIC and SOC will give a more detailed understanding on soil carbon budget than any study on either SOC or SIC alone. Based on the pooled data from Heilongjiang Province, Liaoning Province, Jilin Province and Inner Mongolia Autonomous Region in northeastern China, correlation analyses between variable soil physical-chemical properties and SOC content as well as SIC content were performed in order to find their possible functions in affecting those two components and the potential influence on soil carbon budget estimation in this paper. In general, a larger dataset for SOC (38 to 345 pairs) compared with those for SIC (36 to 122 pairs) was compiled in this paper owing to SIC data shortage. As shown by our results, significant and positive correlations were found between SOC and parameters of total nitrogen, available nitrogen, total phosphorus, available phosphorus, available potassium, exchangeable K⁺ capacity, Fe₂O₃, P₂O₅, total soil porosity (R²=0.10-0.94, n=38-345, P <0.0001), while those for SIC were of significant negative correlations (R²=0.11-0.30, n=37-122, P <0.01) except available P and available K (P>0.05, ns). Given that soil fertilization could affect soil carbon dynamics, this finding indicates that most parameters of soil fertility can contrarily affect the content of SIC and SOC. Furthermore, soil pH and bulk density showed negative correlations with SOC (R²=0.36-0.42, n=41-304, P <0.0001), but they were positively correlated with SIC (R²=0.29-0.31, n=39-125, P <0.01). As obviously manifested by these results, SOC and SIC in northeastern China were markedly correlated with most soil physical-chemical properties, but completely differed in the direction. Land utilization as well as soil management can largely affect soil physical-chemical properties and such changes have already been well-documented. For example, over 30% soil organic matter (SOM) has been lost during the long-term agricultural reclamations and recent studies also found tens of grams of SOC per square meter per year have been accumulated after the return of degraded farmland to forests in this region, but less information is available for SIC. The contrary tendencies of SIC with respect to SOC observed in this paper indicate that inclusion of SIC in the carbon balance calculation may offset the SOC change to some degree. Therefore, in future studies of soil carbon balance, we should pay more attention to the mutual compensatory effect between SOC and SIC, i.e., SOC increases may indicate SIC decreases, or vice versa, and concurrent measurement of SOC and SIC may improve the precision of carbon budget estimation. The empirical equations best-fitted from this study might be used to correct previous bias shown by the lack of SIC represented in former studies. However, this mutual compensatory effect between SIC and SOC will be more sound after long-term studies on permanent plots or well-designed fertilization experiments. Anyway, our results strongly suggest that the general neglect of SIC in current soil carbon research might produce an evident bias in calculation of total carbon budget; especially in some regions with high SIC content, such as the chernozem (a kind of black soil abundant in SIC) widespread in northeastern China.