阿尔泰山西北部垂直带谱中土壤有机氮素分布

阿尔泰山西北部垂直带谱中的土壤有机氮素,同土壤腐殖质一样表现为非连续性的特征转化系列。在干旱气候带,土壤的全氮量随海拔升高到黑钙土增加至10倍。土壤中酸不溶态氮相对含量也持续增加,而氨基酸和氨基糖态氮含量下降。胡敏酸中酸不溶态氮和氨基酸态氮也表现出类似的变化趋势。冷一湿气候带中土壤胡敏酸的未鉴定态氮相对含量明显地多于干旱气候带,而干旱气候带中土壤胡敏酸的酸不溶态氮量显著地高于冷—湿气候带。土壤和其胡敏酸中氮素形态分布,与垂直带谱中土壤的腐殖质化过程紧密相关,随腐殖质化度的增加,酸不溶态氮相对含量提高,而氨基酸态氮和氨基糖态氮量下降。胡敏酸中氨基糖态氮含量甚微。

Soil Organic Nitrogen Distribution in the Vertical Sequence on the Northwestern Slope of Altai Mountains

Temperature and moisture are the two important bio-climatic factors to determine the content and composition of soil organic matter. This work was conducted to investigate the effect of the vertical sequence of bio-climatic condition on the properties of soil organic matter. Altai Mountains is the wet island in the inland arid area. Their soil types and bio-climatic factors varied along with the vertical sequence ascending from an altitude of 500 to 4370 meters above sea level. Six types of soil profile samples and their bioclimatic data were collected. Humic substances were extracted by 0.1M Na_4P_2O_7+0.1M NaOH,then fractionated, purified and ice-dried over P_2O_5. Both soils and humic acids were analyzed for their total carbon, nitrogen and organic nitrogen distribution. The soil vertical sequence on the northwestern slope of Altai Mountains is classified into two kinds of change series, viz., arid climatic (grassland soils) and humid-cold climatic (forest-alpine meadow soils). In both climatic patterns, the warmer climate, the higher percentages of nitrogen in soils occur as amino acid-N and amino sugar-N, which is due to the more extensive decomposition and turnover of organic matter in the soils. The nitrogen percentages of humic acids in the arid climatic series are obviously higher than that in humid-cold climate, and the percentages of hydrolyzable unknown-N(HUN) vice versa. The percentages of nitrogen as acid-insoluble forms were found to increase with an increase in the degree of humification of soils at the expense of decrease of nitrogen in soils as amino acid and amino sugar form. The net effect of the humification process is in conversion of amino acids-N into the structure nitrogen of humic substances. The distribution of organic form nitrogen varied more sensitively with the bio-climatic vertical change in the grassland soils, compared with forest-alpine meadow soils.