外加氮源影响下铁铝氧化物在土壤氮素转化中的作用

Role of Fe and Al Oxides in Soil Nitrogen Transformation under Nitrogen Addition Condition

土壤中铁铝氧化物在团聚体稳定性和有机碳吸附方面具有重要作用,而氮添加对土壤氮循环影响的变化也可能与其有关,但是目前尚缺乏在氮循环方面的研究.为了探究铁铝氧化物在土壤氮素转化中的作用,选择福建省建瓯罗浮栲森林土壤为研究对象,采用选择性溶提技术准备不同的土壤——未经处理(T1)的土壤和去除游离态铁铝氧化物(T2)土壤、去除非晶质铁铝氧化物(T3)土壤、去除络合态铁铝氧化物(T4)土壤,在这些土壤中添加不同形态氮(40 mg/kg)——丙氨酸(氨基酸态氮,AA)、硫酸铵(铵态氮,AN)、硝酸钠(硝态氮,NAN)和亚硝酸钠(亚硝态氮,NIN),进行室内培养试验,分析氮含量变化和氮素转化情况.结果表明:①与CK处理相比,AA和AN处理均增加了T1土壤中w(NH4+-N),NAN处理增加了w(NO3--N),但低于添加量,表明添加氨基酸和铵态氮均会促进氮矿化,添加硝态氮会增加NO3--N的固定且抑制其硝化.②在CK处理下,与T1土壤相比,T2和T4土壤中w(NH4+-N)、w(NO3--N)和w(氨基酸)均降低,但T3土壤中w(NH4+-N)和w(氨基酸)增加、w(NO3--N)降低,表明土壤中游离态氧化铁铝和络合态氧化铁铝的存在有助于氮素矿化,非晶质氧化铁铝有助于硝化.③在不同氮处理下,各土壤的氮含量及其转化速率与CK处理规律相似.与CK处理相比,各氮处理均未显著增加T2和T4土壤中w(NH4+-N),且AA和AN处理均未影响T2、T3和T4土壤中w(NO3--N)和w(氨基酸).结果显示,氮添加并没有改变铁铝氧化物的作用,其中,矿化和氨化作用均表现为游离氧化铁铝>络合氧化铁铝>非晶质氧化铁铝,硝化作用表现为非晶质氧化铁铝>游离氧化铁铝>络合态氧化铁铝.因此,土壤铁铝氧化物的不同存在状态应该是调节氮素转化的重要土壤条件.

Fe and Al oxides play an important role in the stability of soil aggregates and organic carbon adsorption. It is possible that the changes in the effects of nitrogen addition on soil nitrogen transformation are related to Fe and Al oxides. However,there is a lack of research on the role of Fe and Al oxides in soil nitrogen cycling. In order to explore the role of Fe and Al oxides in soil nitrogen transformation,the soils from Castanopsis fabric forest in Jian’ou County of Fujian Province were selected. Different soils were prepared by selective stripping techniques: native soil (T1),removing free Fe and Al oxides (T2),removing amorphous Fe and Al oxides (T3) and removing complex Fe and Al oxides (T4). Incubation experiments were conducted after adding amino acids (AA),ammonium nitrogen (AN),nitrate nitrogen (NAN),and nitrite nitrogen (NIN). The changes in nitrogen content and net transformation rate were investigated. The results showed that: (1) Compared with CK,AA and AN treatments in T1 soil significantly increased w (NH4+-N),and NAN treatment increased w (NO3--N),which was lower than the added amount. These results indicated that addition of amino acids and ammonium nitrogen promoted nitrogen mineralization, and nitrate addition increased NO3--N fixation and inhibited nitrification. (2) Under CK treatment,compared with T1,w (NH4+-N),w (NO3--N) and w (amino acid) in T2 and T4 soils decreased. But in T3 soil,w (NH4+-N) and w (amino acid) increased,and w (NO3--N) decreased. These results suggested that the presence of free Fe and Al oxides and complex Fe and Al oxides was conducive to nitrogen mineralization,while amorphous Fe and Al oxides was conducive to nitrification. (3) Under different nitrogen treatments,the nitrogen content and transformation rate of each soil were similar to those of CK treatment. Compared with CK,each nitrogen treatment did not increase w (NH4+-N) in T2 and T4 soils. In addition,AA and AN treatments did not affect w (NO3--N) and w (amino acid) in T2,T3 and T4 soil. The results indicated that nitrogen addition did not change the role of Fe and Al oxides. The order of Fe and Al oxides in mineralization and ammonification was: free Fe and Al oxides >complex Fe and Al oxides > amorphous Fe and Al oxides,and in nitrification was: amorphous Fe and Al oxides > free Fe and Al oxides >complex Fe and Al oxides. Therefore,the presence of Fe and Al oxides in soil may be an important condition for regulating nitrogen transformation.