径流输入性氮在生物滞留系统中的转化与归趋

Transformation and Fate of Incoming Nitrogen Associated with Runoff in Bioretention System

为探究径流输入性氮在生物滞留系统多介质中的即时转化规律与归趋特性,以水、植物、土壤、微生物等多介质中的氮素为研究对象,采用^(15)N同位素示踪技术考察场次径流输入性氮在多介质中的即时赋存形态与含量,分析不同前期干旱天数(ADD)形成的干湿交替条件下氮的转化特性与多介质归趋。结果表明,径流输入性NO_(3)^(-)-N可同时发生反硝化与硝酸盐异化还原成铵(DNRA)作用,且两者存在协同性。适当的干旱可促进气态氮排放,使其成为NO_(3)^(-)-N的主要归趋路径。但干旱也增加了淋洗排放风险,尤其是长期干旱(ADD=22 d)会抑制反硝化与DNRA作用,显著增加淋洗排放归趋分配比例(高达32.30%)。土壤对NO_(3)^(-)-N的非生物固定和微生物固持作用随ADD的增加而减弱,但长期干旱条件下根际耐干旱微生物成优势菌后可强化土壤的归趋作用,并通过协同竞争作用促进植物对NO_(3)^(-)-N的直接吸收。径流输入性NH_(4)^(+)-N在干旱条件下易以NO-3-N形式发生淋洗排放,但淋洗排放比例最大仅为0.34%。土壤对NH_(4)^(+)-N的归趋以微生物固持作用为主,且归趋分配比例显著高于NO_(3)^(-)-N。干旱期土壤含水率可调控微生物固持和非生物固定作用发生的空间与强度。植物对NH_(4)^(+)-N的吸收主要与植物生物量有关,且营养和水分双重胁迫作用会促进植物根系对NH_(4)^(+)-N的吸收。以上结果证实,不同形态氮在多介质中的即时转化路径和分配比例受ADD影响而存在较大差异,且长时间干旱易发生NO_(3)^(-)-N淋洗排放。

In order to explore the immediate transformation and the fate of incoming nitrogen associated with runoff in multi-media of bioretention systems,such as water,plants,soil,and microbes,the immediate occurrence and content of incoming nitrogen in multi-media were studied with ^(15)N isotope tracing technology.And the transformation of nitrogen under different drying-rewetting regimes which forming through antecedent dry days(ADD)were analyzed.Results showed that there existed denitrification and dissimilatory nitrate reduction to ammonium(DNRA)with cooperativity simultaneously for incoming NO_(3)^(-)-N.Appropriate aridity promoted the emission of gaseous nitrogen,and then it became the dominant fate for NO_(3)^(-)-N.However,aridity also aggrandized the risk of nitrogen leaching,particularly in overlong drought(ADD of 22 d),in which denitrification and DNRA can be inhibited,resulting in an increase of partitioning ratio in leaching fate(up to 32.30%).The abiotic fixation(AF)and microbial immobilization(MI)of soil to NO_(3)^(-)-N was attenuated with the increase of ADD,while rhizosphere microorganism living in an arid environment during an overlong drought could strengthen the fate of nitrogen in the soil,and which facilitated direct assimilation of plants to NO_(3)^(-)-N with a synergistic and competitive effect.The incoming NH_(4)^(+)-N was easy to leaching in the state of nitrate during arid soil conditions,but the leaching ratio only up to 0.34%.The soil fate of NH_(4)^(+)-N was dominated by MI,and the fate partitioning ratio was significantly higher than NO_(3)^(-)-N.The occurring space and intensity of AF and MI were controlled by the soil moisture content during dry period.The assimilation of plants to NH_(4)^(+)-N was mainly related to plant biomass,and it was found that the dual stress effect of nutrients and water in the soil could accelerate the uptake of plant roots to NH_(4)^(+)-N.This research presented here confirmed that the path of immediate transformation and partitioning characteristic of different nitrogen in multi-media were controlled by ADD,which resulted in a quite different,and the leaching of NO_(3)^(-)-N in bioretention system was likely to occur suffering in a prolonged drought.