Damashek Julian, Smith Jason M, Mosier Annika C, Francis Christopher A
Department of Environmental Earth System Science, Stanford University Stanford, CA, USA.
Front Microbiol. 2015 Jan 8;5:743. doi: 10.3389/fmicb.2014.00743. eCollection 2014.
Nitrogen pollution in coastal zones is a widespread issue, particularly in ecosystems with urban or agricultural watersheds. California's Sacramento-San Joaquin Delta, at the landward reaches of San Francisco Bay, is highly impacted by both agricultural runoff and sewage effluent, leading to chronically high nutrient loadings. In particular, the extensive discharge of ammonium into the Sacramento River has altered this ecosystem by vastly increasing ammonium concentrations and thus changing the stoichiometry of inorganic nitrogen stocks, with potential effects throughout the food web. This debate surrounding ammonium inputs highlights the importance of understanding the rates of, and controls on, nitrogen (N) cycling processes across the delta. To date, however, there has been little research examining N biogeochemistry or N-cycling microbial communities in this system. We report the first data on benthic ammonia-oxidizing microbial communities and potential nitrification rates for the Sacramento-San Joaquin Delta, focusing on the functional gene amoA (which codes for the α-subunit of ammonia monooxygenase). There were stark regional differences in ammonia-oxidizing communities, with ammonia-oxidizing bacteria (AOB) outnumbering ammonia-oxidizing archaea (AOA) only in the ammonium-rich Sacramento River. High potential nitrification rates in the Sacramento River suggested these communities may be capable of oxidizing significant amounts of ammonium, compared to the San Joaquin River and the upper reaches of San Francisco Bay. Gene diversity also showed regional patterns, as well as phylogenetically unique ammonia oxidizers in the Sacramento River. The benthic ammonia oxidizers in this nutrient-rich aquatic ecosystem may be important players in its overall nutrient cycling, and their community structure and biogeochemical function appear related to nutrient loadings. Unraveling the microbial ecology and biogeochemistry of N cycling pathways, including benthic nitrification, is a critical step toward understanding how such ecosystems respond to the changing environmental conditions wrought by human development and climate change.
沿海地区的氮污染是一个普遍存在的问题，尤其是在有城市或农业流域的生态系统中。加利福尼亚州的萨克拉门托 - 圣华金河三角洲位于旧金山湾的内陆地区，受到农业径流和污水排放的严重影响，导致长期高营养负荷。特别是，大量铵排入萨克拉门托河改变了这个生态系统，大幅增加了铵浓度，从而改变了无机氮库的化学计量，对整个食物网产生潜在影响。围绕铵输入的这场辩论凸显了了解整个三角洲氮（N）循环过程的速率和控制因素的重要性。然而，迄今为止，很少有研究考察该系统中的氮生物地球化学或氮循环微生物群落。我们报告了萨克拉门托 - 圣华金河三角洲底栖氨氧化微生物群落和潜在硝化速率的首批数据，重点关注功能基因amoA（编码氨单加氧酶的α亚基）。氨氧化群落存在明显的区域差异，只有在铵含量丰富的萨克拉门托河中，氨氧化细菌（AOB）的数量超过氨氧化古菌（AOA）。与圣华金河和旧金山湾上游相比，萨克拉门托河较高的潜在硝化速率表明这些群落可能能够氧化大量的铵。基因多样性也呈现出区域模式，以及萨克拉门托河中系统发育独特的氨氧化菌。这个营养丰富的水生生态系统中的底栖氨氧化菌可能是其整体营养循环的重要参与者，它们的群落结构和生物地球化学功能似乎与营养负荷有关。阐明包括底栖硝化作用在内的氮循环途径的微生物生态学和生物地球化学，是理解此类生态系统如何应对人类发展和气候变化带来的不断变化的环境条件的关键一步。
