Decoupling of microbial glucose uptake and mineralization in soil
Decoupling of microbial glucose uptake and mineralization in soil
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DOI：
10.1016/j.soilbio.2007.09.008
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发表时间：
2008-03-01
影响因子：
9.7
通讯作者：
Jones, David L.
中科院分区：
文献类型：
--
作者：
Hill, Paul W.;Farrar, John F.;Jones, David L.
土壤中有机质周转的速率是陆地碳循环的一个重要组成部分，通常通过测量呼吸作用来估算。可靠的估计要求同位素标记的底物吸收到土壤微生物生物量及其随后的矿化几乎同时发生(即没有时间延迟)。在这里，我们使用添加到农业土壤中的葡萄糖来研究这一范例。从田间采集后，立即向土壤中加入不同浓度的C-14标记葡萄糖(i PM至10 mM)，并在添加底物后1-60分钟测量土壤溶液的耗竭。同时测定了葡萄糖矿化产生的(CO2)-C-14。微生物从土壤溶液中吸收葡萄糖是浓度依赖的，动力学分析表明，至少有两个不同亲和力的不同葡萄糖运输系统运行。在反映土壤溶液中天然葡萄糖浓度(54+/-10 mM)时，外源葡萄糖的半衰期(t(1/2))在S 30左右非常迅速。在较高的葡萄糖浓度(100 mM~10 mM)下，高亲和力载体的t(1/2)值变化不大，但增加的葡萄糖被低亲和力转运系统所占据。土壤微生物群落的葡萄糖矿化在吸收到微生物生物量后表现出明显的延迟，这表明葡萄糖的吸收与随后的呼吸作用脱钩，这可能是由于葡萄糖在不稳定的代谢物库中被稀释所致。通过对矿化结果的双一级动力学方程的拟合，我们估算了自然土壤溶液葡萄糖浓度下第一个快速呼吸阶段的t(1/2)为6-8min，但在矿化之前，添加的葡萄糖至少有87%保留在微生物生物量中。我们的结果表明，在这种土壤中，土壤溶液葡萄糖池每天翻转100-1000次，比通过矿化测量确定的速度快一个数量级。这些结果表明，使用二氧化碳测量底物周转的传统同位素测量可能大大低估了它们在土壤中的循环速度。(C)2007爱思唯尔有限公司。保留所有权利。
The rate of organic matter turnover in soil is a critical component of the terrestrial carbon cycle and is frequently estimated from measurements of respiration. For estimates to be reliable requires that isotopically labelled substrate uptake into the soil microbial biomass and its subsequent mineralization occurs almost simultaneously (i.e. no time delay). Here we investigated this paradigm using glucose added to an agricultural soil. Immediately after collection from the field, various concentrations of C-14-labeled glucose (I PM to 10 mM) were added to soil and the depletion from the soil solution measured at 1-60 min after substrate addition. (CO2)-C-14 production from the mineralization of glucose was simultaneously measured. The microbial uptake of glucose from soil solution was concentration-dependent and kinetic analysis suggests the operation of at least two distinct glucose transport systems of differing affinity. At glucose concentrations reflecting those naturally present in the soil solution (54 +/- 10 mu M), the half-time (t(1/2)) of exogenous glucose was extremely rapid at ca. 30 s. At higher glucose concentrations (100 mu M to 10 mM), the t(1/2) values for the high-affinity carrier were altered little, but increasing proportions of glucose were taken up by the low affinity transport system. Glucose mineralization by the soil microbial community showed a significant delay after its uptake into the microbial biomass suggesting a decoupling of glucose uptake and subsequent respiration, possibly by dilution of glucose in labile metabolite pools. By fitting a double first order kinetic equation to the mineralization results we estimated the t(1/2) for the first rapid phase of respiration at natural soil solution glucose concentrations to be 6-8 min, but at least 87% of the added glucose was retained in the microbial biomass prior to mineralization. Our results suggest that in this soil the soil solution glucose pool turns over 100-1000 times each day, an order of magnitude faster than when determined from measurements of mineralization. These results imply that traditional isotopic based measurements of substrate turnover measured using CO2 may vastly underestimate their rate of cycling in soil. (c) 2007 Elsevier Ltd. All rights reserved.