Co-occurrence of in-stream nitrogen fixation and denitrification across a nitrogen gradient in a western US watershed
Co-occurrence of in-stream nitrogen fixation and denitrification across a nitrogen gradient in a western US watershed
复制标题
DOI：
10.1007/s10533-018-0461-y
复制
发表时间：
2018-07-01
期刊：
影响因子：
4
通讯作者：
Baxter, Colden V.
中科院分区：
文献类型：
--
作者：
Eberhard, Erin K.;Marcarelli, Amy M.;Baxter, Colden V.
人们经常假设固氮 (N-2) 固定和反硝化不会在河流中同时发生，因为每个过程在不同浓度的溶解无机氮 (DIN) 下都有利于，因此这些过程很少一起量化。我们询问这些过程是否可以通过使用乙炔还原和使用乙炔块反硝化进行 N-2 固定的空间调查来共存[有或没有修正碳 (C) 作为葡萄糖和氮 (N) 作为硝酸盐]。对爱达荷州东南部 8 条溪流中的岩石和沉积物进行了速率测量，其 DIN 梯度为 26-615 A mu g L-1。 2015 年和 2016 年夏季在每个地点重复采样。我们发现反硝化和 N-2 固定都发生在 DIN 浓度梯度上，其中 N-2 固定主要发生在岩石上，反硝化发生在沉积物中。在研究的 1 年内，岩石上的 N-2 固定率在 DIN 梯度上显着下降了 100 倍，而修正后的（使用 N 和 C）反硝化率在这两年中在 DIN 梯度上增加了 10 倍。在整个河流河段范围内测量环境特征的多元线性回归和偏最小二乘模型表明，C 和磷是修正和未修正反硝化率的正向预测因子，但没有显着的模型可以解释所有河流和年份的 N-2 固定率。再加上可检测到的 N-2 固定主要发生在岩石上和反硝化主要发生在沉积物上的观察结果表明，微生境尺度因素可以更好地预测河流河段内这些过程的同时发生。忽视河流生态系统中 N-2 固定和反硝化的潜在同时发生，将过分简化每个过程对氮循环的贡献，从而妨碍理解。
It is frequently assumed that nitrogen (N-2) fixation and denitrification do not co-occur in streams because each process should be favored under different concentrations of dissolved inorganic nitrogen (DIN), and therefore these processes are rarely quantified together. We asked if these processes could co-exist by conducting a spatial survey of N-2 fixation using acetylene reduction and denitrification using acetylene block [with and without amendments of carbon (C) as glucose and nitrogen (N) as nitrate]. Rates were measured on rocks and sediment in 8 southeastern Idaho streams encompassing a DIN gradient of 26-615 A mu g L-1. Sampling at each site was repeated in summer 2015 and 2016. We found that both denitrification and N-2 fixation occurred across the gradient of DIN concentrations, with N-2 fixation occurring primarily on rocks and denitrification occurring in sediment. N-2 fixation rates on rocks significantly decreased 100x across the DIN gradient in 1 year of the study, and amended (with N and C) denitrification rates increased 10x across the DIN gradient in both years. Multiple linear regression and partial least squares models with environmental characteristics measured at the scale of entire stream reaches showed that C and phosphorus were positive predictors of amended and unamended denitrification rates, but no significant model could explain N-2 fixation rates across all streams and years. This, coupled with the observation that detectable rates of N-2 fixation occurred primarily on rocks and denitrification occurred primarily on sediment, suggests that microhabitat scale factors may better predict the co-occurrence of these processes within stream reaches. Overlooking the potential co-occurrence of N-2 fixation and denitrification in stream ecosystems will impede understanding by oversimplifying the contribution of each process to the N cycle.