不同肥力棕壤全氮和微生物量氮对外源玉米残体氮的响应

以棕壤玉米长期连作定位试验(27a)形成的高低两种肥力水平土壤为研究对象,采用~(15)N标记的玉米植株为试验试材,分别向两种土壤中加入玉米根、茎、叶(共8个处理),采用室内模拟培养与~(15)N同位素示踪技术,旨在弄清玉米根、茎、叶添加后不同肥力土壤全氮含量及微生物量氮的变化规律。结果表明:(1)添加玉米根、茎、叶后低肥力棕壤全氮含量提升幅度分别比高肥力棕壤高5.75%、4.77%和3.75%,外源新氮的贡献率分别比高肥力棕壤高3.54%、3.28%和2.49%,说明不同肥力土壤对玉米残体添加的响应程度不同,低肥力棕壤对外源新氮施入后的响应更敏感,固定能力更强。(2)在添加玉米残体的56d培养时间内,低肥力棕壤中微生物量氮平均增加0.83—0.98倍,高肥力棕壤中微生物量氮平均增加0.87—1.56倍,可以看出不同部位玉米植株添加后均能显著促进土壤微生物量氮的积累,说明外源有机物输入是刺激土壤微生物数量和活性的重要因素,并且在高肥力土壤中刺激作用更加显著。此外,高肥力土壤添加茎和叶处理微生物量氮显著高于根添加处理,但低肥力土壤中根、茎和叶添加处理土壤中微生物量氮之间无显著差异。外源有机氮输入对土壤氮库的贡献与土壤的肥力水平及不同残体部位自身的物质组成特性密切相关。

Effect of maize-derived nitrogen supplementation on the total and microbial biomass nitrogen of brown earths with different fertility levels

In order to investigate the effect of adding plant residues on total and microbial biomass nitrogen, an incubation experiment was carried out by adding ¹⁵N-labeled maize (Zea mays L.) leaves, stems, or roots to brown earths with different fertility levels. The soil samples were collected from a long-term fertilization experiment site (27 years) that had both low fertility (LF) and high fertility soil (HF). The ¹⁵N stable isotope labeling technique has been used to monitor the accumulation dynamics of maize-derived N in different fertility soils. Our results showed that (1) the addition of roots, leaves, and stems increased the total N content of LF soils by 5.75, 4.77, and 3.75%, respectively, when compared to that of corresponding HF soils. Moreover, the proportion of the total N derived from maize was significantly higher in the LF soils supplemented with roots (3.54%), stems (3.28%), and leaves (2.49%) than in the HF soils. These results suggested that low fertility soil was more sensitive to organic input and had a greater ability to sequester extraneous N. (2) During the 56-day incubation period, the microbial biomass N of the LF soils increased by 0.83-0.98, and that of the HF soils increased by 0.87-1.56 times, which indicated that the addition of maize residues stimulated microbial biomass, especially in HF soils. In addition, there was no significant difference in the microbial biomass of the LF soils supplemented with different maize parts. However, in the HF soils, the addition of stems and leaves had a more pronounced effect on microbial biomass compared than the addition of roots. We conclude that the contribution of exogenous organic N to the total pool of soil N is dependent on both the initial soil fertility and the biochemical composition of the plant residues.