太湖乔木林河岸植被缓冲带截留氮素效率

为研究河岸植被缓冲带对氮素的截留效率，以太湖流域平缓坡地上人工林河岸缓冲带作为研究对象，分析了不同河岸缓冲带宽度（5，15，30，40 m），不同植物类型（‘南林95’杨Populus×euramericana ‘Nanlin 95’林、中山杉Taxodium hybrid ‘Zhongshanshan’林、南林杨95-中山杉混交林）对不同深度径流水及土壤中氮素的截留效果。结果表明:15 m宽的河岸缓冲带即能很好地截留各形态氮素，40 m缓冲带对径流水中硝态氮、铵态氮、总氮的截留率分别达68.8%，68.7%和66.0%；同一宽度条件下，缓冲带对40 cm深径流水中铵态氮、总氮的截留率较高，分别达71.4%和69.1%，对20 cm深径流水中硝态氮截留率较高，达70.6%；森林土壤对铵态氮和硝态氮的截留主要在中层土壤，对总氮截留主要在表层土壤；杨树林缓冲带对径流水中铵态氮和硝态氮的截留率较高（P < 0.05），达77.4%和66.3%；杨树-中山杉混交林缓冲带对总氮的截留率较高（P < 0.05），达73.0%；植物叶片（r=-0.53）全氮和土壤总氮（r=-0.59）均与径流水中总氮呈负相关关系。

Removing nitrogen with trees planted in the riparian vegetation buffer strips of Taihu Lake

In the Taihu Lake area many riparian vegetation buffer strips have been built to alleviate the input of eutrophic nutrients into the lake. To provide a scientific basis for determining a suitable width and components of these riparian buffer strips, the effects of riparian vegetation buffer strips with widths of 5, 15, 30, and 40 m and vegetation types of a Populus×euramericana 'Nanlin 95' plantation, an Taxodium hybrid 'Zhongshanshan' plantation, and a mixed plantation with the two tree species on total nitrogen, ammonia nitrogen, and nitrate nitrogen removal rates for different depths of runoff water and soil were studied. Results showed that the buffer strips of 15 m width effectively removed various fractions of N and removal rates in runoff water of 40 m width of 68.8% for NO₃-, 68.7% for NH₄+, and 66.0% for total N. Removal rates of NH₄+ and total N in runoff water at 40 cm below ground level were higher, reached 71.4% and 69.1%, but NO₃- removal rate in the 20 cm depth of runoff water was higher, reached 70.6%. The interceptions of NH₄+ and NO₃- in plantation soils were mainly in the middle soil layer, and total N was trapped mainly in surface soils. The poplar plantation had a higher removal rate of NH₄+ and NO₃- in runoff water(P < 0.05), reached 77.4% and 66.3%, but the mixed forests of the poplar plantation and Taxodium hybrid 'Zhongshanshan' plantation had a higher removal rate of total N(P < 0.05), reached 73.0%. Also, total N in runoff water was negatively correlated to total N in the soil (r=-0.59) and total N in the leaves (r=-0.53) of plants.