外源氮输入对不同土地利用排水沟底泥反硝化和N2O排放影响

农田排水沟通过底泥硝化-反硝过程可消纳部分农业面源氮.水稻、蔬菜和水果是太湖地区种植业的主要土地利用类型,各种植区排水河沟密布,且不同种植区沟道接受外源氮差异明显,直接影响沟道消纳氮能力.分别采集太湖地区果园、稻田和菜地种植区排水沟道沉积物,设计上覆水N0、N1、N2、N3和N4这5个外源NO-3-N输入梯度,净氮输入量分别为0、0.5、1.0、5.0和10 mg·L~(-1),开展室内培养试验,研究外源氮输入对不同土地利用区排水沟道底泥反硝化和N2O排放的影响.结果表明,外源氮输入激发了排水沟底泥反硝化作用,3条沟道底泥反硝化速率均随上覆水NO-3-N输入浓度增大显著增大(P0.05),底泥累积反硝化量与输入NO-3-N浓度呈显著线性正相关关系(R20.75);除菜地外,沟道底泥N2O排放速率和累积排放量随外源NO-3-N输入浓度增大均无显著增大趋势(P0.05).在无外源氮或低外源氮输入时(N0和N1),果园、菜地和稻田种植区3种沟道之间底泥反硝化和N2O排放累积损失氮量的差异不显著(P0.05).随NO-3-N输入浓度增大,特别是高外源氮输入(N3和N4)条件下,果园和稻田排水沟道底泥反硝化消纳氮量显著高于菜地沟道底泥反硝化损失氮量(P0.05),而菜地排水沟底泥N2O排放损失氮量显著高于其它2条沟道底泥的N2O排放损失氮量(P0.05).排水沟底泥有机碳矿化速率与反硝化损失速率成正相关关系(n=15),微生物矿化(CO2-C)作用促进了沟道底泥硝化反硝过程.

Impact of Exogenous Nitrogen Import on Sediment Denitrification and N2O Emissions in Ditches Under Different Land Uses

Farmland drainage ditch soil can consume part of the agricultural non-point nitrogen through nitrification-denitrification processes. Paddy fields, vegetable land, and orchards are the main types of land uses in the Taihu Lake region, and many drainage ditches are distributed across these lands. The way exogenous nitrogen is imported to drain ditches under different land uses differs significantly, which can directly affect the nitrogen consumption ability of the channels. A soil incubation experiment was conducted under laboratory conditions to study the denitrification loss and N₂O emissions of drainage ditch soil under different land uses. In this study, drainage ditch sediment was collected from orchards, paddy fields, and vegetable land in the Taihu Lake region. Five different NO₃^--N content import levels were set:0, 0.5, 1.0, 5.0, and 10 mg·L^-1, which were denoted as N₀, N₁, N₂, N₃, and N₄, respectively. The results showed that exogenous nitrogen input stimulated sediment denitrification in the drainage ditches. The sediment denitrification rates of the three types of channels increased significantly with the increase of input NO₃^--N concentration (P<0.05). There was a significant linear positive correlation between the cumulative denitrification loss and input NO₃^--N concentration (R²>0.75). Excluding for the vegetable land sediment, the N₂O emission rate and cumulative emissions did not increase significantly with the increase of input NO₃^--N concentration (P>0.05). There was no significant difference in the denitrification and N₂O emissions among the three kinds of channel sediment, with no or low exogenous nitrogen input (N₀and N₁) (P>0.05). As the input NO₃^--N concentration increased, especially under the condition of high exogenous nitrogen input (N₃and N₄), the nitrogen consumed via denitrification in orchard and paddy field sediment was significantly higher than that in vegetable land sediment (P<0.05), whereas the N₂O emissions of drainage ditch sediment from the vegetable land was significantly higher than that of the other two channel sediments (P<0.05). The mineralization rate of ditch soil organic carbon had a positive correlation with denitrification rate (n=15), and microbial mineralization (CO₂-C) promoted the nitrification and denitrification of the drainage ditch soils.