枯萎期芦苇收割时间对湿地脱氮效果及根系呼吸代谢的影响

Effects of Reed(Phragmites australis)Harvest Time on Nitrogen Removal and Root Respiratory Metabolism in Wetland

冬季植物枯萎会影响湿地的脱氮效果,而收割是湿地植物最主要的管理措施之一.为探讨亚热带地区芦苇不同收割时间对冬季湿地的脱氮效果和湿地植物功能的影响,运用水平潜流湿地开展了2年〔第1年(2017年7月—2018年3月)进水ρ(TN)为17.60~34.65 mg/L,第2年(2018年8月—2019年4月)进水ρ(TN)为3.16~10.03 mg/L〕不同收割时间(W1为不收割、W2为枯萎前收割、W3为枯萎中期收割、W4为枯萎末期收割)试验,以研究枯萎期湿地脱氮效果和芦苇根系呼吸代谢特征对收割时间的响应.结果表明:①2年试验均表现为收割后湿地脱氮效果降低,与枯萎前和枯萎中期收割相比,枯萎末期收割对湿地TN和NH_(4)^(+)-N的去除率降低程度较小.②进水ρ(TN)较高的年份,枯萎前收割显著增强芦苇冬季的根系活力以及己糖激酶(HK)、丙酮酸激酶(PK)、磷酸果糖激酶(PFK)活性,湿地氮去除率的变化整体上由异柠檬酸脱氢酶(ICDH)和HK活性主导;进水ρ(TN)较低的年份,收割处理对根系活力以及HK、PK、PFK活性的影响不大,但HK活性对湿地氮去除率的影响最大.③2年试验的收割处理均降低了根系ICDH和细胞色素氧化酶(COX)活性,但枯萎末期收割对其影响程度相对较小.研究显示,冬季湿地脱氮效果与根系呼吸代谢特征存在一定相关性,枯萎末期收割芦苇对湿地脱氮效果和根系呼吸代谢的影响较小.

Wetlands are ecotones between aquatic and terrestrial ecosystems,and play an important role in intercepting nitrogen sources on the land and reducing nitrogen levels in water bodies.Plants play a very important role in removing nitrogen in wetlands,and the plant harvesting(cutting)time affects the removing efficiency.During the plant wilting period(winter),there is inevitably a low nitrogen removal efficiency from wetlands.Understanding the optimal harvest time of reed(Phragmites australis)will allow the use of management practices to balance the trade-off between nitrogen removal and the sustainability of wetlands.An experiment was set up to investigate the nitrogen removal efficiency and root respiratory metabolism in reed wetlands for two years(discontinuity harvesting between years;the first year(from July 2017 to March 2018),influent TN 17.60-34.65 mg L;the second year(from August 2018 to April 2019),influent TN 3.16-10.03 mg/L)).To identify the optimal harvest time:W1(un-harvest),W2(harvest before wilting),W3(harvest at mid-wilting),and W4(harvest at late wilting).The results showed that:(1)Harvesting decreased wetland nitrogen removal in both years,with later harvest time producing a smaller decrease in total nitrogen(TN)and ammonium(NH_(4)^(+)-N)removal.(2)The root activity and hexokinase(HK),pyruvate kinase(PK)and phosphofructokinase(PFK)activities were significantly enhanced in winter when harvest before wilting in the year with higher influent TN concentration,and the wetland nitrogen removal was dominated by isocitric dehydrogenase(ICDH)and HK activities.While harvest time had little effect on root activity and HK,PK and PFK activities in the year with lower influent TN concentration,and HK activity had the greatest effect on wetland nitrogen removal.(3)The root ICDH and cytochrome oxidase(COX)activities decreased in both two-year experiments,but the effect of late wilting harvest was relatively small.The results show that there is considerable relationship between nitrogen removal in wetland and the characteristics of root respiration metabolism in winter,which is affected by the harvest time.