Clear increases in acetylene reduction by soil bacteria from an East Siberian Taiga forest bed under conditions mimicking the natural soil environment
Clear increases in acetylene reduction by soil bacteria from an East Siberian Taiga forest bed under conditions mimicking the natural soil environment
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DOI：
10.1111/j.1747-0765.2010.00512.x
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发表时间：
2010-10-01
影响因子：
2
通讯作者：
Hatano, Ryusuke
中科院分区：
文献类型：
--
作者：
Hara, Shintaro;Hashidoko, Yasuyuki;Hatano, Ryusuke
在北方森林生态系统中，氮素失衡长期以来一直被认为是其高生物量生产的一个谜。在大豆根瘤菌（Bradyrhizobium japonicum）广泛使用的条件下，林床土壤中的微生物群通常不会显示出任何显着的乙炔还原。然而，在最近的一项研究中，东西伯利亚针叶林床中的土壤细菌微生物群和从土壤中分离的细菌在用结冷胶代替琼脂固化的贫氮软凝胶培养基中显示出显着的乙炔还原。因此，我们精确地研究了包括培养基组成在内的最佳培养条件;土壤微生物群的适当条件确定如下：0.5 g L-1 d-甘露醇作为碳源，10-15 ℃孵育温度和培养基pH 6.2。这些文化条件类似的物理化学条件的活动层在东西伯利亚北部森林床的冻土。事实上，甘露醇，这是最合适的碳源，获得作为一个主要的糖成分的越橘根垫，覆盖在这个地区的落叶松林床。最有利的浓度的d-甘露醇（0.5克L-1）的乙炔还原是只有1/20或1/30的碳源的量在世界范围内的乙炔还原测定。以类似的方式，10-15摄氏度，这是最有利的孵化温度范围，接近夏季散装土壤活性层的报告温度。因此，即使在3.0 g L-1结冷胶培养基中，在模拟土壤条件下的乙炔还原测定导致测试的细菌群落的乙炔还原明显增加。由于世界范围内测定条件与土壤环境的距离太远，北方森林床土的固氮潜力一直被评价得很低。
In boreal forest ecosystems, nitrogen imbalance has long been discussed as a mystery with regard to its high biomass production. Under conditions widely used for the soybean nodulation bacterium Bradyrhizobium japonicum, microbiota in forest bed soil often do not show any significant acetylene reduction. However, in a recent study, soil bacterial microbiota in an East Siberian Taiga forest bed and bacteria isolated from the soil show remarkable acetylene reduction in nitrogen-poor soft-gel medium solidified with gellan gum instead of agar. Thus, we precisely investigated optimal culture conditions including compositions of the medium; appropriate conditions for the soil microbiota were determined as follows: 0.5 g L-1 d-mannitol as the carbon source, 10-15 degrees C incubation temperature and medium pH 6.2. These culture conditions resembled the physicochemical conditions of the active layer in the East Siberian boreal forest bed on the permafrost. In fact, mannitol, which was the most appropriate carbon source, was obtained as a major sugar component of the cowberry root mats that cover the larch forest bed in this region. The most profitable concentration of d-mannitol (0.5 g L-1) for acetylene reduction was only 1/20 or 1/30 of the amount of the carbon source used in worldwide acetylene reduction assays. In a similar manner, 10-15 degrees C, which was the most profitable incubation temperature range, was close to the reported temperature of the active layer of the bulk soil in summer. Thus, even in a 3.0 g L-1 gellan gum medium, an acetylene reduction assay under the imitated soil conditions led to clear increases in acetylene reduction of the bacterial communities tested. The N-2-fixing potential of boreal forest bed soil had thus ever been evaluated unfairly low, because the world wide assay conditions were too far from the soil environments.