亞熱帶地區7種典型林分土壤有機氮組分特征1)

耿必苗 孫慶業 武林輝 王艷杰 陳月 趙瓊

(安徽大學，合肥，230601)

This study was conducted to understand characteristics of total nitrogen (N) and organic N components in different types of forest soils in subtropical China. Soil total N and organic N components determined by Bremner acid hydrolysis method were compared in seven types of forests, i.e. mixed broad-leaved forest, Phyllostachys edulis forest, Liquidambar formosana forest, mixed coniferous and broad-leaved forest, Pinus massoniana forest, Cunninghamia lanceolata forest and mixed coniferous forest. In addition, the correlations between soil N components and physicochemical properties were analyzed. The forest type has a significant effect on the contents of total N and organic N components. The contents of non-acid hydrolysis N and acid hydrolysis ammonia N are highest in Phyllostachys edulis forest, while the other organic N components and total N contents are highest in mixed broad-leaved forest. With the increase of the soil depth, the contents of total N, non-acid hydrolysis N, acid hydrolysis N and its components show a downward trend. Soil acid hydrolysis N accounting for 68.06% of total N is the predominant part of soil N. The content of each component of organic nitrogen and its proportion to total nitrogen in descending order are on-acid hydrolysis N and unknown N, amino acid N and acid hydrolysis ammonia N, and amino sugar N.

土壤氮素可分為無機態氮和有機態氮兩類，其中有機態氮約占土壤總氮的90%以上[1]。土壤中有機氮質量分數及其生物學穩定性的大小決定土壤供氮潛能的大小[2]。一直以來，人們認為有機態氮必須經過微生物礦化作用轉變為無機態氮才能為植物所用，然而，目前已有證據表明，如氨基酸這樣的小分子氮可直接被植物吸收利用[3-4]。土壤中已知的有機氮化合物種類繁多，包括各種蛋白質、氨基糖等，但由于其組成相似，很難被分離鑒定[5]。Bremner[6]于1965年提出利用酸解法分組測定土壤有機氮，并將有機氮分為酸解氮(酸解氨態氮、氨基酸態氮、氨基糖態氮、未知態氮)和非酸解氮。此后，國內外學者對土壤有機氮組分展開了大量研究，主要集中于其在施肥[7-9]、灌溉[10-11]、土壤類型[12-14]、土地利用方式[15]等方面的變化特征。施肥可以提高土壤有機氮組分質量分數及供氮潛力[8-9]；滴灌及滲灌處理的氨基酸態氮、酸解氨態氮、氨基糖態氮占全氮的比例均高于溝灌[11]；旱地土壤的總氮及各組分氮質量分數均顯著低于相應的水稻土壤[15]。已有研究發現，亞熱帶典型森林土壤中有機氮組分隨土壤深度的增加呈下降趨勢[16]，土壤總氮及有機氮組分質量分數隨著馬尾松恢復年限的增加而增加[17]，但對不同類型森林土壤有機氮組分特征的研究及報道較為少見。

近年來受人類活動的影響，我國亞熱帶地區森林資源遭到破壞，其地帶性自然優勢群落被大量破壞，取而代之的是大面積的次生林和人工林，因此，或多或少存在生產力低、土壤肥力退化和樹種組成單一化等問題[18]。……