人工遮光和营养添加对河流反硝化活性和反硝化细菌群落结构的影响

河流生态系统受到人类活动例如河岸带森林植被毁损和农业活动施肥等的干扰日益加剧,而这些活动使河流接收的光照增多、河流的氮磷营养盐浓度增加。微生物的反硝化作用是河流去除氮的有效途径。在汉江的一级支流金水河上游核心保护区内选取6条溪流开展野外控制实验,利用营养添加模拟河流中营养的增加,遮盖河面来模拟源头溪流的隐蔽状态,来研究河流沉积物中微生物的反硝化作用对光照和营养改变的响应,并利用高通量测序(Mi Seq)技术研究在两种处理下河流沉积物中nir S型反硝化细菌的群落结构变化。结果显示:营养元素添加促进了沉积物的反硝化活性,河面遮盖抑制了沉积物的反硝化活性。营养添加和遮盖两种处理均降低了控制实验区域内脱氯单胞菌属(优势菌属)的相对丰度,同时也降低了该区域nir S型反硝化菌群落的Chao多样性。本研究初步证实了光照增加和河流的营养增加提高了河流沉积物反硝化活性,并为提高河流的脱氮能力提供科学依据。

Influences of artificial shading and nutrient addition on denitrification activity and community structure of denitrifying bacteria in a stream

River ecosystems have been disturbed and aggravated by increasing human activities including those activities wherein forest area is changed to agricultural area in riparian zones and intensive fertilizer usage in agriculture. These anthropogenic activities lead to an increase in the light received by the surface of the river and nutrient (nitrogen and phosphorus) enrichment in the river. Denitrification driven by microorganisms in sediments is the most important path for the removal of nitrogen from aquatic ecosystems. The alteration of light intensity influences the denitrification process owing to the change in the amount of available organic carbon produced via the metabolism of algae and photosynthetic bacteria. We added slow-releasing fertilizer into the river to simulate nutrient enrichment similar to the effect of fertilization from the agricultural industry. We also covered a part of the stream surface to achieve conditions similar to those of rivers in headwaters with thick forest coverage. We selected six streams to conduct manipulated experiments at the core area in the natural reserve in the upper Jinshui River, Hanjiang, to assess the responses of denitrification to the different treatments-nutrient addition and coverage. We also analyzed subsequent changes in community structure and diversity of bacteria using the encoding nirS gene by MiSeq high-throughput sequencing technology. The results showed that artificial shading above streams can reduce the denitrification activity of sediments, relative abundances of dominant bacteria (Dechloromonas) and the diversity of bacteria as indicated by the encoding nirS gene. Furthermore, nutrient addition into the stream increased the denitrification activity of sediments, whereas there was a decrease in relative abundance of dominant bacteria and the diversity of bacteria. The preliminary results confirmed the increase in denitrification activity of stream sediments as a result of increasing light intensity and nutrient content. This study has allowed us to understand the denitrifying capacity of rivers and provides scientific primary data for river management.