Effect of soil mixing on nitrification rates in soils of two deciduous forests of Vermont, USA
Effect of soil mixing on nitrification rates in soils of two deciduous forests of Vermont, USA
复制标题
土壤混合对美国佛蒙特州两片落叶林土壤硝化率的影响
作者：
A. Kaur;D. Ross;G. Fredriksen
采样干扰已被证明在一些森林土壤中迅速增加净硝化速率。为了深入了解机理，我们调查了完整岩芯和混合复合样品中氨化和硝化的总速率和净速率。使用同位素池稀释法，我们研究了美国东北部的两个分水岭，佛蒙特州的刷子溪和睡眠河，以前的工作发现那里的净硝化率很高。总氨化作用在完整岩芯和混合样品之间通常没有显著差异。然而，混合样品的总硝化速率和净硝化速率相似(平均∼24 /N kg−1 hr−1或∼8 mg/N kg−1 d−1)，显著高于完整岩芯(毛和净平均值分别为7.7和3.4 /N/kg−1 h−1)。硝酸盐消耗量在一定程度上受到干扰的影响而减少，但不能解释净化率的巨大差异。由于两个处理的总氨化速率相似，这些扰动土壤中硝化作用的增加肯定是氨氧化菌对氨的利用增加的结果，而牺牲了其他氨的消耗途径。不同的土壤可能有不同的作用机制；在这些氮素循环速率较高的土壤中，增加硝化作用似乎是主要途径。
Sampling disturbance has been shown to rapidly increase net nitrification rates in some forest soils. To gain insight on mechanisms, we investigated both gross and net rates of ammonification and nitrification in intact cores and mixed composite samples. Using the isotope pool dilution method, we studied samples from two northeastern USA watersheds, Brush Brook and Sleepers River in Vermont, where previous work had found high net nitrification rates. Gross ammonification was usually not significantly different between intact cores and mixed samples. However, gross and net nitrification rates in mixed samples were similar (mean ∼24 µmol N kg−1 hr−1 or ∼8 mg N kg−1 d−1) and significantly higher than in intact cores (7.7 and 3.4 µmol N kg−1 h−1 for means of gross and net respectively). Nitrate consumption was decreased somewhat by disturbance but did not account for the large differences in net rates. Because there were similar gross ammonification rates in both treatments, increased nitrification in these disturbed soils must be a result of an increase in the utilization of ammonium by the ammonia oxidizers at the expense of other ammonium consumption pathways. Different mechanisms may operate in different soils; increased nitrification appears to be the primary pathway in these soils with high N cycling rates.