Wang Weibo, Wang Xu, Shu Xiao, Wang Baoru, Li Hongran, Zhang Quanfa
CAS Key Laboratory of Aquatic Botany and Watershed Ecology, Wuhan Botanical Garden, Chinese Academy of Sciences, Wuhan 430074, China.
Center of Plant Ecology, Core Botanical Gardens, Chinese Academy of Sciences, Wuhan 430074, China.
Microorganisms. 2021 Oct 22;9(11):2202. doi: 10.3390/microorganisms9112202.
Sediment particle size and heterogeneity play an important role in sediment denitrification through direct and indirect effects on, for example, the material exchange rate, environmental gradients, microbial biomass, and grazing pressure. However, these effects have mostly been observed in impermeable sediments. On the other hand, the material exchange of permeable sediments is dominated by advection instead of diffusion, with the exchange or transport rates exceeding those of diffusion by two orders of magnitude relative to impermeable sediments. The impact of permeable sediment particle size and heterogeneity on denitrification remains poorly understood, especially at the millimeter scale. Here, we conducted an in situ control experiment in which we sorted sand sediment into four homogeneous-particle-sizes treatments and four heterogeneous treatments. Each treatment was deployed, in replicate, within the riffle in three different river reaches with contrasting physicochemical characteristics. After incubating for three months, sediment denitrifier communities (nirS, nirK, nosZ), denitrification gene abundances (nirS, nirK, nosZ), and denitrification rates in all treatments were measured. We found that most of the denitrifying microbes in permeable sediments were unclassified denitrifying microbes, and particle size and heterogeneity were not significantly correlated with the functional gene abundances or denitrification rates. Water chemistry was the key controlling factor for the denitrification of permeable sediments. Water NO-N directly regulated the denitrification rate of permeable sediments, instead of indirectly regulating the denitrification rate of sediments by affecting the chemical characteristics of the sediments. Our study fills a knowledge gap of denitrification in permeable sediment in a headwater river and highlights that particle size and heterogeneity are less important for permeable sediment denitrification.
沉积物粒径和异质性通过对物质交换率、环境梯度、微生物生物量和捕食压力等产生直接和间接影响，在沉积物反硝化过程中发挥着重要作用。然而，这些影响大多是在不透水沉积物中观察到的。另一方面，透水沉积物的物质交换以平流为主而非扩散，其交换或传输速率相对于不透水沉积物超过扩散速率两个数量级。透水沉积物粒径和异质性对反硝化的影响仍知之甚少，尤其是在毫米尺度上。在此，我们进行了一项原位对照实验，将砂质沉积物分为四种均匀粒径处理和四种非均匀处理。每种处理在具有不同理化特征的三条不同河段的浅滩中重复设置。孵育三个月后，测量了所有处理中沉积物反硝化菌群落（nirS、nirK、nosZ）、反硝化基因丰度（nirS、nirK、nosZ）和反硝化速率。我们发现，透水沉积物中的大多数反硝化微生物是未分类的反硝化微生物，粒径和异质性与功能基因丰度或反硝化速率没有显著相关性。水化学是透水沉积物反硝化的关键控制因素。水中的硝态氮直接调节透水沉积物的反硝化速率，而不是通过影响沉积物的化学特征间接调节沉积物的反硝化速率。我们的研究填补了源头河流中透水沉积物反硝化方面的知识空白，并强调粒径和异质性对透水沉积物反硝化的重要性较低。
