茶树对可溶性有机和无机态氮的吸收与运转特性

摘要

[目的]揭示亚热带茶树能否直接吸收利用分子态可溶性有机氮,探讨茶树吸收可溶性有机和无机氮后的运转特性差异. [方法]采用13C、15y双标记甘氨酸、15N标记硫酸铵和15N标记硝酸钾为同位素示踪剂,采用茶树(黄金桂)幼苗为试验材料进行同位素示踪盆栽试验,用同位素质谱仪测定茶树植株地上和地下部的13C、15N丰度.[结果]供试土壤施用13C、15N双标记甘氨酸态有机氮后,2h和6h茶苗地下部和整株中的13C增量/15N增量比值均接近于1∶1的理论值;2h和6h茶苗地上部未检出13C增量,而72h地上部13C增量达0.284 μmol/(g,DW);施用铵态氮2h、6h和72 h茶苗地下部、地上部和整株中的15N增量均极显著高于施用硝态氮和甘氨酸态有机氮;施用铵态氮6h茶苗地上部 15N增量/地下部15N增量比率分别比硝态氮和甘氨酸态有机氮的比率高34.7％和65.0％,72 h茶苗地上部15N增量/地下15N增量比率分别比硝态氮和甘氨酸态有机氮的比率高88.6％和133.0％,差异均达极显著水平. [结论]黄金桂茶苗具有从土壤中直接吸收利用甘氨酸分子态有机氮的能力,但吸收量不及铵态氮和硝态氮;吸收的可溶性分子态有机氮可以从茶树根系运转至地上部;不同形态氮素在茶树植株体内的迁移能力高低表现为:铵态氮＞硝态氮＞甘氨酸态氮,该研究结果进一步证明陆地生态系统植物直接吸收利用可溶性有机氮是普遍存在的现象.%[Objectives] Whether tea plants in subtropics could directly take up soluble molecular organic nitrogen from soil or not does not have agreeable conclusions.Studying the transport charecteristics of soluble organic and inorganic nitrogen in tea plants will help the deep understanding of the problem.[Methods] The isotope tracing method was used in a pot experiment using tea seedlings (Huangjingui) as tested material.The isotope tracers were 2-13C-15N-glycine,(15NH4)2SO4 and 15N-KNO3,which were injected into soil at the bottom of tea seedlings.Aboundance of 13C and 15N in shoots and roots were measured by isotope ratio mass spectrometer with a Eurovector Elemental Analyser.[Results] The ratios of 13C to 15N excess in roots and whole seedlings of Huangjingui were much close to 1 ∶ 1,the theroretical ratio of 13C to 15N aboundance,at 2 h and 6 h after the 2-13C-15N-glycine application in soil.The 13C excess was not detected in Huangjingui shoots at 2 h and 6 h,while it reached 0.284 μmol/(g,DW) in shoots at 72 h after the 2-13C-15N-glycine application.The 15N excesses of roots,shoots and whole seedlings of Huangjingui at 2 h,6 h and 72 h after the (15NH4)2SO4 application were significantly higher than those after the 15N-KNO3 and 2-13C-15N-glycine application in soil.The shoot/root ratio in 15N excess at 6 h after the (15NH4)2SO4 application was 34.7％ and 65.0％ higher than those after the 15N-KNO3 and 2-13C-15N-glycine application,while the ratio at 72 h after the (15NH4)2SO4 application was 88.6％ and 133.0％ higher than those after the 15N-KNO3 and 2-13C-15N-glycine application,respectively,and the differences of the ratios between the (15NH4)2SO4 and 15N-KNO3 or 2-13C-15N-glycine treatments reached the 1％ level.[Conclusions] Tea plants of Huangjingui could directly take up intact glycine molecule from the soil,but preferred to uptake ammonium-N and nitrate-N.The glycine molecule taken up by Huangjingui could be transported from roots to shoots.The transport ability of different forms of nitrogen in Huangjingui plants showed following order:ammonium-N ＞ nitrate-N ＞ glycine-N.These results provided further evidence that uptake of soluble organic N by plants is a widespread adaptation strategy in terrestrial ecosystems.