The potential for feedback effects induced by global warming on emissions of nitrous oxide by soils
The potential for feedback effects induced by global warming on emissions of nitrous oxide by soils
复制标题
DOI：
10.1046/j.1365-2486.1997.00100.x
复制
发表时间：
1997-08-01
影响因子：
11.6
通讯作者：
Smith, KA
中科院分区：
文献类型：
--
作者：
Smith, KA
约65%的一氧化二氮排放来自土壤，由好氧硝化和厌氧反硝化作用引起。热带森林土壤可能是最重要的单一来源，其次是耕作土壤。自然系统中的排放速率与有机质的氮矿化速率和氮沉积有关；在农业系统中，排放速率与用作肥料的氮素的数量有关，在相关情况下，还与最近的土地利用变化有关。全球N2O预算并不平衡，来源可能仍被低估。全球变暖对N2O排放产生积极反馈的直接证据来自对冰芯中空气的研究。未来全球变暖的预计影响之一是北部泥炭地地下水位的下降；实验表明，这将导致排放量增加，但对总排放量的影响将很小。在非泥炭地土壤上进行的许多实验结果表明，温度对土壤排放的影响总体上是积极的，当反硝化作用是主要过程时，增加的速度可能会非常陡峭。过程水平的模拟表明，原因是土壤呼吸增加，导致发生反硝化的厌氧量增加，以及温度上升直接带来的单位厌氧量反硝化率的增加。这些结果表明，通常情况下，土壤排放的正反馈是可能的。然而，在一些环境中，很大比例的年排放总量可能发生在冻融循环期间；这种循环可能会变得或多或少频繁，这取决于气候区域，这可能会因全球变暖而产生积极或消极的反馈效应。全球和区域趋势模型对气候影响通量的方向和大小给出了非常矛盾的预测，但正反馈的预测似乎更可靠。
About 65% of all emissions of nitrous oxide, N2O, are from soils, and are caused by aerobic nitrification and anaerobic denitrification. Tropical forest soils are probably the most important single source, followed by cultivated soils. Emission rates in natural systems are related to the rate of N mineralization from organic matter, and N deposition; in agricultural systems they are related to the quantities of N used as fertilizers and, where relevant, to recent land use change. The global budget for N2O is not well balanced, and sources may still be underestimated. Direct evidence of a positive feedback of global warming on N2O emissions comes from studies of air in ice cores. One of the projected effects of future global warming is a lowering of water tables in northern peatlands; experiments suggest that this would lead to increased emissions, but that the effect on total emissions would be small. The results of many experiments with non-peatland soils indicate that the effect of temperature on soil emissions is generally positive, and that the rate of increase may be very steep when denitrification is the principal process involved. process-level modelling suggests that the reason is increased soil respiration, which causes an increase in anaerobic volume in which denitrification can take place, in addition to the increased denitrification rate per unit anaerobic volume brought about directly by the rise in temperature. These results imply that generally a positive feedback on emissions from soils is likely. However, in some environments, a large proportion of total annual emissions can occur during freeze-thaw cycles; such cycles may become more or less frequent, depending on the climatic zone, and this may result in either a positive or negative feedback effect due to global warming. Models of global and regional trends give very conflicting predictions of the direction and the magnitude of climatic impacts on fluxes, but the prediction of a positive feedback seems to be the more soundly based.