植物种类对野芷湖湖岸带土壤反硝化作用的影响

反硝化作用是湖岸带有效去除氮素的关键氮循环过程,受到植物、土壤理化性质及微生物等因素的影响。为探究湖岸带不同植物对土壤反硝化作用的影响,通过调查测定野芷湖湖岸带9种常见植物的根际与非根际土壤的反硝化功能基因丰度和反硝化潜势,分析其与土壤理化性质的关系,阐明植物种类影响反硝化作用的机制。研究结果表明:(1)种植植物会改变湖岸带土壤的理化指标,植物根际土的硝态氮(NN)、铵态氮(AN)、总碳(TC)、总氮(TN)和可溶性有机碳(DOC)含量等显著高于非根际土,其中柳树、黄素馨、喜旱莲子草根际土的TC、DOC、TN、NN显著高于其他物种,桂树的根际和非根际土的pH均显著低于其他物种;(2)植物根际土的微生物反硝化功能基因(narG、napA、nirS、nirK和nosZ)丰度显著高于非根际土,其中柳树、黄素馨、喜旱莲子草根际土的基因丰度显著高于其他物种, pH、TN、NN和DOC等对反硝化功能基因丰度影响较大;(3)根际土的反硝化潜势显著高于非根际土,其中柳树、桂树、黄素馨根际土的反硝化潜势显著高于其他物种,黄素馨非根际土的反硝化潜势也较高,pH、DOC、TN以及napA、nirS、norB基因丰度等对土壤的反硝化潜势具有显著影响。本研究说明植物根际微环境更有利于反硝化微生物的生长与繁殖,湖岸带种植植物时可考虑不同的常绿和落叶乔木、灌木、草本植物的合理配置来提高湖岸带的氮素截留能力,以减少由过量氮素进入水生生态系统导致的面源污染。

Effects of plant species on soil denitrification in the lakeshore zone of Yezhi Lake

The lakeshore zone is a transitional zone between aquatic ecosystem and terrestrial ecosystem, which can reduce the impact of nonpoint source pollution. Plants are key parameters to prevent and control nitrogen migration into the lakeshore zone. Denitrification is a key process in the nitrogen cycle for the effective removal of nitrogen in the lakeshore zone, which can be affected by plant species, soil physicochemical properties, and microorganisms. In order to explore the effects of plant species on soil denitrification and the mechanism, the soil denitrification potential and denitrifying functional gene abundance of rhizosphere and non-rhizosphere of nine common plant species in the lakeshore zone of Yezhi Lake, and their relations with soil physicochemical properties were elucidated. The results showed that: (1) different plant species planting in the lakeshore zone changed the soil physicochemical properties. The contents of ammonium (NN), nitrate (AN), total carbon(TC), total nitrogen (TN), and soluble organic carbon (DOC) in the rhizosphere soils of all sampled species were significantly higher than those in the non-rhizosphere. The TC, DOC, TN, and NN in the rhizosphere soils of Salix babylonica, Jasminum nudiflorum, and Alternanthera philoxeroides were significantly higher than those of other plant species, while the pH of both rhizosphere and non-rhizosphere soils of Osmanthus fragrans were significantly lower. (2) The abundances of soil denitrifying functional genes, including narG, napA, nirS, nirK, and nosZ in the rhizosphere soils were significantly higher than those in the non-rhizosphere. The gene abundances in the rhizosphere soils of S. babylonica, J. nudiflorum, and A. philoxeroides were significantly higher than those of other plant species. pH, TN, NN, and DOC had significant impacts on the abundance of soil denitrification functional genes. (3) The soil denitrification potentials of the rhizosphere soils (0.44-1.99 mg N kg^-1h^-1) were much higher than those of non-rhizosphere soils (0.14-0.48 mg N kg^-1h^-1), with the rhizosphere soil denitrification potential of S. babylonica, O. fragrans, and J. nudiflorum significantly higher among the nine plant species, and the soil denitrification potential of J. nudiflorum was the highest in the non-rhizosphere soils. pH, DOC, TN, napA, nirS, and norB significantly affected the soil denitrification potential of the Yezhi lakeshore zone. The study indicates that denitrifying microorganisms grow vigorously in the plants'' rhizosphere microenvironment, and plant species enhance the soil denitrification intensity of the lakeshore zone significantly and differently. Various species of evergreen and deciduous trees, shrubs and herbs were suggested in the planting arrangement of lakeshore zone, so as to increase the nitrogen retention capacity of lakeshore zone and reduce the nonpoint source pollution caused by excessive nitrogen entering the aquatic ecosystem.