Abstract:

Soil is the largest reservoir of organic carbon in terrestrial ecosystems, and small changes in it have a huge impact on the global carbon cycle. Iron oxides in soil play an important role in the fixation of organic carbon, but the effect of different types of iron oxides on the fixation of organic carbon remains to be further studied. This study selected two kinds of zonal soil in the south and north of China, designed a culture experiment of adding straw, and took regular samples during the 24 months of culture. The contents of different types of organic matter and iron oxides in soil were determined and their correlations were obtained. The spatial distribution of iron oxides and organic functional groups with straw and time was obtained by synchrotron radiation infrared spectroscopy (SR-FTIR). The results showed that: 1) the balance of organic carbon in Red soil reached after 12 months of cultivation, and the balance of organic carbon in Black soil was broken after 20 months of cultivation; 2) In Red soil, there was a significant positive correlation between crystalline iron and total organic carbon (r=0.519, p<0.01), and a significant negative correlation between amorphous iron and total organic carbon (r=−0.454, p<0.01) and humic acid (r=−0.434, p<0.01), indicating that crystalline iron promoted the fixation of organic carbon in Red soil. In Black soil, there was a significant positive correlation between crystalline iron and total organic carbon and humic acid, with r values of 0.545 and 0.643, respectively. There was a significant negative correlation with dissolved organic carbon (r=−0.433, p<0.01). The results show that crystalline iron promotes the fixation of solid components in organic carbon in Black soil. 3) Synchrotron radiation infrared results showed that clay minerals and iron oxides preferentially fixed fatty carbon in two different soil treatments; In Red soil, time promoted the binding of two kinds of minerals with various types of organic carbon, and straw promoted the binding of iron oxides with various types of organic carbon. In Black soil, the combination of the two types of minerals and various types of organic carbon is more affected by time. These results show that crystalline iron plays an important role in the fixation of organic carbon in both soils, and time promotes the aggregation of minerals and organic matter in Red soil, while the opposite result is found in Black soil, where straw promotes the binding of iron oxides and organic carbon. This study revealed the dynamic change process of various types of organic carbon and iron oxides when exogenous straw was added to Red soil and Black soil, and clarified the role of various types of iron oxides on organic carbon fixation, which could provide a theoretical basis for organic carbon management in Red soil and Black soil.

Key words: soil organic carbon, iron oxides, soil components, straw turnover, synchrotron radiation infrared spectrum, mineral conservation

摘要：

土壤是陆地生态系统中最大的有机碳库，其微小的变化对全球碳循环影响巨大。土壤中铁氧化物对有机碳的固定起重要作用，但不同类型的铁氧化物对有机碳固定的影响还有待进一步研究。选取南、北方两种地带性土壤，设计添加秸秆的培养试验，培养24个月，定期取样。测定土壤中不同类型有机碳和铁氧化物含量并获得其相关性；利用同步辐射红外光谱技术得到铁氧化物、有机物官能团随秸秆、时间变化的空间分布等信息。研究结果表明，1）秸秆还田后，红壤中有机碳在培养12个月后到达平衡，黑土中有机碳在培养20个月后分解量增加；2）在红壤中，晶型铁与总有机碳呈极显著正相关（r=0.519，p<0.01），非晶型铁与总有机碳（r=−0.454，p<0.01）、腐殖酸呈极显著负相关（r=−0.434，p<0.01），说明晶型铁对红壤有机碳的固定起促进作用。在黑土中，晶型铁与总有机碳、腐殖酸呈极显著正相关，r值分别为0.545和0.643；与溶解性有机碳呈极显著负相关（r=−0.433，p<0.01），说明在黑土中晶型铁对有机碳固相组分的固定起促进作用；3）同步辐射红外结果显示，在两种土壤不同处理中，粘粒矿物、铁氧化物优先固定脂肪碳；在红壤中，时间促进了两类矿物与各类型有机碳的结合，秸秆促进了铁氧化物与各类型有机碳的结合；在黑土中，两类矿物与各类型有机碳的结合受时间影响更大。该研究揭示了外源秸秆添加到红壤和黑土中，各类型有机碳、铁氧化物的动态变化过程，明确了各类型铁氧化物对有机碳固定的作用，可为红壤及黑土中有机碳管理提供理论依据。

关键词: 土壤有机碳, 铁氧化物, 土壤组分, 秸秆还田, 同步辐射红外光谱, 矿物保护