【目的】简便、快速、准确地测定树干茎流氮化学特征对于揭示森林生态系统养分循环和群落演替机制具有重要意义。本研究以期建立以紫外分光度法为基础、准确测定树干茎流总氮、硝酸盐氮、亚硝酸盐氮和氨态氮的方法。【方法】以神农架地区8种乔木的茎流为材料，从双波长紫外分光光度法、硝酸根电极法、麝香草酚法和酚二磺酸法中筛选出测定树干茎流硝酸盐氮( F)的最优方法；利用过硫酸钾能将茎流中氨态氮和亚硝酸盐氮彻底氧化为硝酸盐氮的特性，采用紫外分光光度法、硝酸根电极法分别测定其总氮( T)并加以比较；利用高锰酸钾仅能氧化亚硝酸盐氮而不能氧化氨态氮的特性，建立紫外分光光度法测定其硝酸盐氮和亚硝酸盐总合量( B)的方法；最后计算出亚硝酸盐氮(等于 B-F)和氨态氮(等于 T-B)含量，并与纳氏试剂法直接测定氨态氮含量进行比较。【结果】在测定硝酸盐氮( F)的4种方法中，紫外分光光度法最好，其回收率为106.19%±8.26%，相对标准偏差3.0%，硝酸根电极法耗时长且稳定性较差，麝香草酚法测定步骤较繁琐，酚二磺酸法的准确性较差；过硫酸钾氧化氧化后，紫外分光光度测定茎流总氮( T)的回收率达到94.62%±2.19%，相对标准偏差2.0%，而硝酸根电极法测定的准确性较差，相对标准偏差偏高(7.0%)；高锰酸钾氧化后，采用紫外分光光度法测定树干茎流亚硝酸盐氮和硝酸盐氮合量( B)的加标回收率为100.97%±2.85%，相对标准偏差4.0%；通过紫外分光光度法测定并计算的氨态氮、亚硝酸盐氮相对标准偏差分别为3.0%和4.0%。【结论】树干茎流经过硫酸锌氢氧化钠溶液处理后，可使用紫外分光光度法直接测定其硝酸盐氮含量(F)，经过硫酸钾氧化后可以使用紫外分光光度法测定其总氮(T)，经过高锰酸钾氧化后可以使用紫外分光光度法测定硝酸盐氮与亚硝酸盐氮的总合量( B)，计算得出的亚硝酸盐氮(等于 B-F)和氨态氮含量(等于 T-B)具有准确性。%Objective]In studies of nitrogen cycling of forest system,it is important to determine nitrate nitrogen,nitrite nitrogen,ammonia nitrogen and total nitrogen of tree stem-flow accurately,the aim of this paper was to develop a method to measure the contents of these chemical properties with UV spectrophotometer.[Method]Stem flow of 8 canopy tree species from Shenlongjia Mountain were selected to measure nitrate nitrogen ( F) content in the stem-flow using 4 common methods, including UV spectrophotometry,nitrate electrode,phenol disulfonic acid and thymol,and to decide which method was the best for detecting nitrate nitrogen ( F ) content; the stem-flow was oxidize at 125 ℃ for 45 minutes by using refined potassium persulfate solution and total nitrogen ( T ) was then detected using UV spectrophotometer and nitrate cathode respectively. The stemflow was oxidized with potassium permanganate solution and the total content of nitrate and nitrite ( B) was s then measured with UV spectrophotometer. The content of nitrite was calculated as B-F,and ammonia as T-B,then the content of ammonia was compared with that detected by the method of Nessler ’s reagent. [Results]The UV spectrophotometry was the best method among the 4 methods in detecting nitrate nitrogen,with an accuracy and a precision of 106. 19% ± 8. 26% and 3. 0%,respectively; the accuracy and precision of nitrate cathode,thymol and phenoldisulfonic acid were102. 5% ± 12. 08%and 2. 0%,107. 44% ± 9. 26% and 4%,43. 62% ± 26. 39%and 12%,respectively. The accuracy and precision of total nitrogen ( T) measured with UV spectrophotometry were 94. 62% ± 2. 19% and 2. 0%; In contrast,the accuracy of nitrate electrode method was 98. 93% ± 37. 64%%,indicating that it was not applicable to some tree species. Accuracy and precision of nitrate and nitrite(B) measured with UV spectrophotometry were 100. 97% ± 2. 85%and 4. 0%,indicating that it was perfect in detecting nitrate and nitrite. The precision of ammonia and nitrite calculated from T,F and B were up to 3. 0% and 4. 0% respectively,suggesting that our method was suited for detecting ammonia and nitrite. [Conclusion]Tree stemflow could be oxidized with potassium persulfate and potassium permanganate,then nitrate nitrogen ( F ) , total nitrogen ( T ) and total content of nitrite and nitrate all can be measured directly with UV spectrophotometer,and nitrite and ammonia of stemflow could be calculated with them.
展开▼
