| Difference of soil organic nitrogen components and microbial biomass nitrogen under different eco-system in northwestern China |
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| DOI：10.7606/j.issn.1000-7601.2004.04.03 |
| Key Words: soil organic nitrogen component microbial biomass nitrogen |
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| Abstract: |
| 12 soil samples collected from forestland，meadow，steppe，and farmland under different ecological systems in northwestern China were used to study soil organic nitrogen components and the relationship of soil microbial biomass nitrogen with organic nitrogen components．The soil organic nitrogen components were determined by acidic hydrolysable method，and soil microbial biomass nitrogen was analyzed by fumigation-waterlogged incubation method．The results showed that there existed variation among organic nitrogen component amounts of the soils in different eco-system，but the variation had the same tendency as the soil total nitrogen content，and the organic nitrogen component contents in natural soil was higher than that in arable soil．However，the ratio of soil organic nitrogen component to total nitrogen was relatively steady．The acidic hydrolysable nitrogen ranged from 472．7to 4021．9 mgN／kg with a average of 1303．5±1153．2mgN／kg，and occupied 72．76％±4．01％ of total nitrogen；with increase of soil depth，the ratio of acidic hydrolysable nitrogen to total nitrogen was decreasing： The average ratio was 77．1％±3．96％（ n＝3） in 0～20cm soil and 70．1％±2．48％ in 20～40cm soil. Unhydrolysable nitrogen ranged from 181．1to 1888．1mgN／kg with a average of 509．9±21．7mgN／kg， occupied 27．33％±4．02％ of total nitrogen；and the ratio of acidic unhydrolysable nitrogen to total nitrogen in 0～20cm soil was lower than that in 20～40cm soil．Among the acidic hydrolysable organic nitrogen components，NH3－N （ ranged from 81．8to 662．5mg N／kg with a average of 233．7±226．9 mgN／kg） ，amino sugar nitrogen （ ranged from46．0to665．3mgN／kg with a average of162．1±184．6mg／kg） ，amino acid nitrogen （ range from 191．5to 2283．9mgN／kg with a average of 671．4±685．8mgN／kg） and unknown nitrogen （ ranged from 101．6to 430．6mgN／kg with a average of 237．1±117．9mgN／kg） contained in acidic hydrolyzable nitrogen occupied12．85％±3．03％，8．13％±1．91％，34．24％±4．21％ and 17．48％±8．55％ of total nitrogen respectively．The results also indicated that there was a successive reducing tendency of microbial biomass nitrogen amounts from forest soil （403．2mg N／kg） ，to meadow soil （308．4mg N／kg） ，to steppe soil （302．1mg N／kg） ，and to arable soils （ ranged from 62．4 to 137．2mg N／kg） ．However microbial biomass nitrogen in natural vegetation soils was much higher than that in arable soils．No matter what the soil eco-environment condition was，microbial biomass nitrogen mainly distributed at 0～20cm soil，and decreased sharply beneath this layer．Very remarkable positive correlation existed in microbial biomass nitrogen and kinds of organic nitrogen components，but the ratio of soil organic nitrogen components to microbial biomass nitrogen was different： acidic hydrolyzable nitrogen （84．6％） was higher than unhydrolysable nitrogen （68．6％） ，among acidic hydrolyzable nitrogen components，NH3－N （86．7％） ＞ amino acid nitrogen （78．9％） ＞ amino sugar nitrogen （66．1％） ＞unkonwn hydrolysable nitrogen（52．0％） ，the contributions of alkaline amino acid to microbial biomass nitrogen was largest （87．2％） ，and the contribution of acidic amino acid，neutral amino acid and sulfur containing amino acid were almost equal to each other，which ranged from 77．6％ to 78．7％． |