Hines ME, Crill PM, Varner RK, Talbot RW, Shorter JH, Kolb CE, Harriss RC
Institute for the Study of Earth, Oceans and Space, University of New Hampshire, Durham, New Hampshire 03824.
Appl Environ Microbiol. 1998 May 1;64(5):1864-70. doi: 10.1128/AEM.64.5.1864-1870.1998.
A dynamic dilution system for producing low mixing ratios of methyl bromide (MeBr) and a sensitive analytical technique were used to study the uptake of MeBr by various soils. MeBr was removed within minutes from vials incubated with soils and ~10 parts per billion by volume of MeBr. Killed controls did not consume MeBr, and a mixture of the broad-spectrum antibiotics chloramphenicol and tetracycline inhibited MeBr uptake by 98%, indicating that all of the uptake of MeBr was biological and by bacteria. Temperature optima for MeBr uptake suggested a biological sink, yet soil moisture and temperature optima varied for different soils, implying that MeBr consumption activity by soil bacteria is diverse. The eucaryotic antibiotic cycloheximide had no effect on MeBr uptake, indicating that soil fungi were not involved in MeBr removal. MeBr consumption did not occur anaerobically. A dynamic flowthrough vial system was used to incubate soils at MeBr mixing ratios as low as those found in the remote atmosphere (5 to 15 parts per trillion by volume [pptv]). Soils consumed MeBr at all mixing ratios tested. Temperate forest and grassy lawn soils consumed MeBr most rapidly (rate constant [k] = 0.5 min-1), yet sandy temperate, boreal, and tropical forest soils also readily consumed MeBr. Amendments of CH4 up to 5% had no effect on MeBr uptake even at CH4:MeBr ratios of 10(7), and depth profiles of MeBr and CH4 consumption exhibited very different vertical rate optima, suggesting that methanotrophic bacteria, like those presently in culture, do not utilize MeBr when it is at atmospheric mixing ratios. Data acquired with gas flux chambers in the field demonstrated the very rapid in situ consumption of MeBr by soils. Uptake of MeBr at mixing ratios found in the remote atmosphere occurs via aerobic bacterial activity, displays first-order kinetics at mixing ratios from 5 pptv to ~1 part per million per volume, and is rapid enough to account for 25% of the global annual loss of atmospheric MeBr.
使用一种用于产生低混合比甲基溴（MeBr）的动态稀释系统和一种灵敏的分析技术，研究了各种土壤对MeBr的吸收情况。在与土壤和体积比约为十亿分之十的MeBr一起孵育的小瓶中，MeBr在几分钟内就被去除了。灭活的对照不消耗MeBr，广谱抗生素氯霉素和四环素的混合物可抑制98%的MeBr吸收，这表明所有的MeBr吸收都是由细菌进行的生物学过程。MeBr吸收的最适温度表明存在一个生物汇，但不同土壤的土壤湿度和最适温度各不相同，这意味着土壤细菌对MeBr的消耗活动是多样的。真核生物抗生素放线菌酮对MeBr吸收没有影响，这表明土壤真菌不参与MeBr的去除。MeBr的消耗在厌氧条件下不会发生。使用动态流通小瓶系统，以低至在偏远大气中发现的混合比（体积比为5至15万亿分之一[pptv]）对土壤进行孵育。在所有测试的混合比下，土壤都消耗MeBr。温带森林和草地土壤消耗MeBr的速度最快（速率常数[k]=0.5分钟-1），但沙质温带、北方和热带森林土壤也很容易消耗MeBr。高达5%的CH4添加量即使在CH4:MeBr比例为10(7)时对MeBr吸收也没有影响，MeBr和CH4消耗的深度剖面表现出非常不同的垂直速率最适值，这表明像目前培养的那些甲烷氧化细菌，在MeBr处于大气混合比时不会利用它。在田间使用气体通量室获得的数据表明，土壤在原位能非常迅速地消耗MeBr。在偏远大气中发现的混合比下，MeBr的吸收是通过需氧细菌活动发生的，在混合比从5 pptv到约百万分之一体积比范围内呈现一级动力学，并且速度足够快，足以解释全球每年大气中MeBr损失的25%。
