Ecosystem Sciences Division, Department of Environmental Science, Policy, and Management, University of California, Berkeley, California 94720, USA.
Ecology. 2010 Sep;91(9):2604-12. doi: 10.1890/09-1365.1.
We report that iron-reducing bacteria are primary mediators of anaerobic carbon oxidation in upland tropical soils spanning a rainfall gradient (3500-5000 mm/yr) in northeast Puerto Rico. The abundant rainfall and high net primary productivity of these tropical forests provide optimal soil habitat for iron-reducing and iron-oxidizing bacteria. Spatially and temporally dynamic redox conditions make iron-transforming microbial communities central to the belowground carbon cycle in these wet tropical forests. The exceedingly high abundance of iron-reducing bacteria (up to 1.2 x 10(9) cells per gram soil) indicated that they possess extensive metabolic capacity to catalyze the reduction of iron minerals. In soils from the higher rainfall sites, measured rates of ferric iron reduction could account for up to 44% of organic carbon oxidation. Iron reducers appeared to compete with methanogens when labile carbon availability was limited. We found large numbers of bacteria that oxidize reduced iron at sites with high rates of iron reduction and large numbers of iron reducers. The coexistence of large populations of iron-reducing and iron-oxidizing bacteria is evidence for rapid iron cycling between its reduced and oxidized states and suggests that mutualistic interactions among these bacteria ultimately fuel organic carbon oxidation and inhibit CH4 production in these upland tropical forests.
我们报告说，在波多黎各东北部跨越降雨梯度（3500-5000 毫米/年）的旱地热带土壤中，还原铁的细菌是厌氧碳氧化的主要介质。这些热带森林丰富的降雨量和高净初级生产力为还原铁和氧化铁细菌提供了最佳的土壤栖息地。空间和时间上动态的氧化还原条件使铁转化微生物群落成为这些湿润热带森林地下碳循环的核心。还原铁细菌的极高丰度（高达每克土壤 1.2 x 10(9)个细胞）表明它们具有广泛的代谢能力来催化铁矿物的还原。在降雨量较高的土壤中，测量的三价铁还原速率可占有机碳氧化的 44%。当可利用的易位碳有限时，铁还原剂似乎与产甲烷菌竞争。我们在还原铁速率较高的地点发现了大量氧化还原铁的细菌，以及大量的铁还原剂。大量的铁还原菌和铁氧化菌共存证明了铁在还原态和氧化态之间的快速循环，这表明这些细菌之间的互利相互作用最终为有机碳氧化提供了动力，并抑制了这些旱地热带森林中的 CH4 产生。
