Weiss Johanna V, Emerson David, Megonigal J Patrick
Environmental Science and Policy Department, George Mason University, Fairfax, VA 22030, USA.
FEMS Microbiol Ecol. 2004 Apr 1;48(1):89-100. doi: 10.1016/j.femsec.2003.12.014.
We compared the reactivity and microbial reduction potential of Fe(III) minerals in the rhizosphere and non-rhizosphere soil to test the hypothesis that rapid Fe(III) reduction rates in wetland soils are explained by rhizosphere processes. The rhizosphere was defined as the area immediately adjacent to a root encrusted with Fe(III)-oxides or Fe plaque, and non-rhizosphere soil was >0.5 cm from the root surface. The rhizosphere had a significantly higher percentage of poorly crystalline Fe (66+/-7%) than non-rhizosphere soil (23+/-7%); conversely, non-rhizosphere soil had a significantly higher proportion of crystalline Fe (50+/-7%) than the rhizosphere (18+/-7%, P<0.05 in all cases). The percentage of poorly crystalline Fe(III) was significantly correlated with the percentage of FeRB (r=0.76), reflecting the fact that poorly crystalline Fe(III) minerals are labile with respect to microbial reduction. Abiotic reductive dissolution consumed about 75% of the rhizosphere Fe(III)-oxide pool in 4 h compared to 23% of the soil Fe(III)-oxide pool. Similarly, microbial reduction consumed 75-80% of the rhizosphere pool in 10 days compared to 30-40% of the non-rhizosphere soil pool. Differences between the two pools persisted when samples were amended with an electron-shuttling compound (AQDS), an Fe(III)-reducing bacterium (Geobacter metallireducens), and organic carbon. Thus, Fe(III)-oxide mineralogy contributed strongly to differences in the Fe(III) reduction potential of the two pools. Higher amounts of poorly crystalline Fe(III) and possibly humic substances, and a higher Fe(III) reduction potential in the rhizosphere compared to the non-rhizosphere soil, suggested the rhizosphere is a site of unusually active microbial Fe cycling. The results were consistent with previous speculation that rapid Fe cycling in wetlands is due to the activity of wetland plant roots.
我们比较了根际和非根际土壤中Fe(III)矿物的反应活性和微生物还原潜力，以检验湿地土壤中快速的Fe(III)还原速率可由根际过程来解释这一假设。根际被定义为紧邻被Fe(III)氧化物或铁胶膜包裹的根的区域，非根际土壤是距离根表面>0.5 cm的土壤。根际中结晶性差的铁的百分比（66±7%）显著高于非根际土壤（23±7%）；相反，非根际土壤中结晶性铁的比例（50±7%）显著高于根际（18±7%，所有情况P<0.05）。结晶性差的Fe(III)的百分比与FeRB的百分比显著相关（r = 0.76），这反映出结晶性差的Fe(III)矿物在微生物还原方面具有不稳定性。非生物还原溶解在4小时内消耗了根际Fe(III)氧化物库的约75%，而土壤Fe(III)氧化物库仅消耗了23%。同样，微生物还原在10天内消耗了根际库的75 - 80%，而非根际土壤库仅消耗了30 - 40%。当用电子穿梭化合物（AQDS）、Fe(III)还原细菌（嗜金属地杆菌）和有机碳对样品进行修正时，两个库之间的差异仍然存在。因此，Fe(III)氧化物矿物学对两个库的Fe(III)还原潜力差异有很大影响。与非根际土壤相比，根际中结晶性差的Fe(III)和可能的腐殖质含量更高，且Fe(III)还原潜力更高，这表明根际是微生物铁循环异常活跃的场所。结果与之前关于湿地中快速的铁循环是由于湿地植物根系活动的推测一致。
