中國西北地區土壤中的微生物體氮

Microbial Biomass Nitrogen in Soils in Northwest China

李生秀(Sheng-Xiu Li) ； 李世清(Shi-Qing Li)

《土壤與環境》 1卷4期 (1998/12) Pp. 307-324

https://doi.org/10.30058/SE.199812.0004

摘要

存在於土壤微生物體中的氮素稱微生物體氮（Microbial biomass N）。這類氮素以數量較大、轉化較快、對土壤供氮能力有重大意義而倍受人們重視。我國西北地區土壤中微生物體氮的研究工作一直無人問津。本研究中我們把燻蒸與淹水培養法結合起來，測定了西北地區不同生態系統土壤中的微生物體氮及其與各種有機氮組成的關係，系統研究了影響微生物體氮的因子。研究表明，微生物體氮含量和生態條件與土壤類型有密切關係，從森林土壤（微生物體氮為403.2 μg N/g）、草甸土壤（340.8 μg N/g）、草原土壤（301.2 μg N/g）到農田土壤（62.4～137.6 μg N/g），依次減低。微生物體氮主要分布在0～20 cm的土層，20～40 cm的土層含量不高。土壤有機質、施肥量、作物根系、溫度和水分明顯地影響微生物體氮含量。不同生態系統土壤中的有機質，均與土壤微生物體氮有高度相關，相關係數達0.844**（n=12）。施用有機肥料或秸稈能為微生物提供能源物質，刺激微生物生長，因而能明顯地提高土壤微生物體氮。在紅油土上進行的長期試驗表明：0∼20 cm表土增的微生物體氮為102.2 μg N/g；施用氮、磷肥，110.4 μg N/g；在施氮、磷肥基礎上，每年每公頃施9375 kg、18750 kg、37500 kg鮮玉米秸稈和37500 kg廄肥，微生物體氮分別是147.2、162.3、286.4和265.3 μg N/g。在黃綿土上進行的長期試驗與此有相同結果。培養試驗證明，在有效能源物質豐富的情況下加入氮肥後雖能發生肥料氮的生物固定，但隨著能源物質減少，新固定的微生物體氮很快礦化，淨固定量甚微。施用氮肥促進了作物地上、地下部分生長，增加了土壤中有機殘體，因而也增加了微生物體氮。根圈土壤微生物體氮為非根圈土壤1.08∼2.04倍（平均1.44倍），說明了根系影響微生物體氮含量。土壤微生物體氮隨溫度而變化，夏季最高，春、秋較高，初冬居中，嚴冬最低；室內測定，4～36℃範圍內，溫度升高，微生物體氮增加，二者有極顯著的線性關係（r=0.99）。土壤含水量從6.7%到11.0%，微生物體氮隨之增加；從11.0%到23.2%，微生物體氮基本穩定。

關鍵字

中國西北 ； 土壤 ； 微生物體氮 ； 影響因子

並列摘要

Nitrogen being contained in living microbial bodies is called microbial biomass nitrogen. More attention has been given to this kind of nitrogen as it occupies a larger portion of the soil nitrogen, it turns over very fast, and it is of significance in reflecting soil nitrogen-supplying capacities. However, the soil's microbial biomass nitrogen in northwest China has not been studied up to now. In the investigation, the fumigation method was combined with the waterlogged incubation to study its contents in different soils under different ecological systems, the relationship between microbial biomass N and the organic N components, and the factors affecting microbial biomass nitrogen amounts.The results show that the microbial biomass N amounts were closely related to ecological conditions and soil types, and there was a great variation from forest soils (403.2 μg N/g) to meadow soils (340.8 μg N/g), to steppe soils (301.2 μg N/g),and to arable soils (from 62.4 to 137.2 μg N/g), decreasing in the above succssive order. The microbial biomass N mainly distributed in 0-20 cm top layer of a soil, and decreased sharply beneath this layer.Soil organic matter contents, fertilizer rates, crop root amounts, temperature and soil moisture greatly influenced its content. The organic matter amounts in different ecological systems were well correlated with the microbial biomass nitrogen, the correlation coefficient being 0.844. Adding organic fertilizers or crop residues to soil provided energy source for soil microorganisms, and thereby stimulated their growth. As a result, the microbial biomass N significantly increased. A long-term experiment conducted on a manual loessial soil shows that the microbial biomass N in 0-20 cm layer was 102.2 μg N/g with no fertilization, and 110.4 μg N/g with application of both N and P fertilizers, whereas addition of 9375 kg, 18750 kg, 37500 kg fresh maize stalk and 37500 kg of organic manure per ha per year on the basis of applying N and P fertilizers raised the microbial biomass N to 147.5, 163.2, 286.4 and 265.3 μg N/g, respectively. Another long-term experiment conducted in a loessial soil obtained similar results. An incubation experiment reveals that after application of N fertilizer, the fixation of fertilizer N into microbial biomass N occurred where highly available energy materials had exited, and the fixed N could rapidly be released with reduction of the materials. Therefore, the net fixed N was almost negligible. Due to crop residues being raised, application of N fertilizer increased the microbial biomass N. The microbial biomass N in rhizosphere soil being as high as 1.08-2.04 times as that in non-rhizosphere soil indicates that roots played a great role in increasing its amounts. The microbial biomass N was greatly associated with soil temperature. Field measurements show that it was the highest in summer and higher in spring and autumn, middle at the beginning of winter, whearas lowest in the hard period of the winter season. A laboratory experiment shows that in the range from 4 to 36℃, the microbial biomass N increased with temperature increase, having a significantly linear relationship between them (r=0.99). It is another story for the relation of soil moisture to the microbial biomass N: the microbial biomass N increased with moisture in the range from 6.7% to 11.0%, while maintaining stable when soil moisture varied from 11.0% to 23.2%.

並列關鍵字

Northwest China ； Soil ； microbial biomass N ； factors affecting microbial biomass N