两种氮浓度对轮叶黑藻(Hydrilla verticillata)腐解过程营养盐释放及附着生物膜内氮循环基因丰度的影响

氨氮是地表水常见污染物,尤其在农业区域,氮类化肥的不合理施用会导致周边水体氮浓度迅速升高并保持较高水平.然而,当前对高氮水平下沉水植物腐败和附着氮循环微生物的影响尚不清楚.以轮叶黑藻(Hydrilla verticillata)为研究用沉水植物,在实验室内模拟水体内8和16 mg/L氮浓度下轮叶黑藻腐解过程中营养盐释放及残体表面微生物氮循环功能基因丰度的变化.研究发现水体两种氮浓度下轮叶黑藻腐解过程中残体腐解及营养盐释放速率无显著差异;与对照相比,植物腐败初期水体内碳、磷浓度迅速增加,而溶解氧浓度及氧化还原电位迅速降低,随着时间的推移上述水质指标逐步恢复至初期状态(第146天);水体荧光溶解性有机质主要包括紫外类富里酸、可见类富里酸、色氨酸类蛋白质和酪氨酸类蛋白质等类型.在5个氮循环相关基因中,氮负荷增加对轮叶黑藻残体生物膜内amo A、napA和narG的丰度有显著影响.冗余分析表明氮循环基因丰度受水体总氮浓度的影响较小,与植物总有机碳含量和水体化学需氧量及溶解氧浓度存在相关性.研究结果表明虽然当前氮水平对植物腐败过程影响不大、对氮循环基因丰度有一定影响,但是对该水生植被(尤其是植物腐败初期)和农业退水排放的管理仍需加强,以降低其对水体的影响.

Impacts of two nitrogen concentrations on nutrients release and nitrogen cycle genes abundance in biofilm during Hydrilla verticillata decomposition

Ammonia nitrogen is a common pollutant in surface water, especially in agricultural areas, because the unreasonable application of nitrogen fertilizer will lead to the rapid increase of nitrogen concentration in surrounding water and maintain a high level. However, little is known about nitrogen loading on the decomposition of submerged macrophytes and N cycle genes in biofilms on plant debris. The alterations in epiphytic microbial abundances of nitrogen cycle-related genes and nutrient release were investigated in decomposition progress of Hydrilla verticillata, simulated in tanks with the concentrations of total nitrogen were 8 and 16 mg/L. The results show that there was no significant difference in the decomposition rates of Hydrilla verticillata residual between treatments with 8 and 16 mg/L total nitrogen. Compared with the control experiment, the dissolved oxygen concentrations and oxidation-reduction potential values decreased while the concentrations of carbon and total phosphorus rapidly increased in overlaying water in the early stage of plant decay. With prolonged decomposition time, the quality of overlying water was almost recovered back to the initial level (146 days). During the plant decomposition, the dissolved organic matter was composed of fulvic acid-like substances (including ultraviolet fulvic acid-like and visible fulvic acid-like) and protein-like substances (including tryptophan and tyrosine). Among five nitrogen cycle genes, changes in abundance of three genes were detected in biofilms on plant debris of two treatments. Redundancy analysis showed that the abundance of nitrogen cycle gene was less affected by the total nitrogen concentration of water, but was correlated with total organic carbon of plants, chemical oxygen demand, and dissolved oxygen concentration in overlaying water. Our results demonstrate that nitrogen loading did not affect the decomposition of plant debris but somewhat altered nitrogen cycle gene abundances in biofilm. However, the management of the aquatic vegetation (especially in the early stage of plant decomposition) and wastewater in the agriculture area still needs to be strengthened to reduce its impact on receiving water body.