This study coupled stable isotope probing with phospholipid fatty acid analysis (¹³C-PLFA) to describe the role of microbial community composition in the short-term processing (i.e., C incorporation into microbial biomass and/or deposition or respiration of C) of root- versus residue-C and, ultimately, in long-term C sequestration in conventional (annual synthetic fertilizer applications), low-input (synthetic fertilizer and cover crop applied in alternating years), and organic (annual composted manure and cover crop additions) maize-tomato (Zea mays – Lycopersicum esculentum) cropping systems. During the maize growing season, we traced ¹³C-labeled hairy vetch (Vicia dasycarpa) roots and residues into PLFAs extracted from soil microaggregates (53–250 μm) and silt-and-clay (<53 μm) particles. Total PLFA biomass was greatest in the organic (41.4 nmol g⁻¹ soil) and similar between the conventional and low-input systems (31.0 and 30.1 nmol g⁻¹ soil, respectively), with Gram-positive bacterial PLFA dominating the microbial communities in all systems. Although total PLFA-C derived from roots was over four times greater than from residues, relative distributions (mol%) of root- and residue-derived C into the microbial communities were not different among the three cropping systems. Additionally, neither the PLFA profiles nor the amount of root- and residue-C incorporation into the PLFAs of the microaggregates were consistently different when compared with the silt-and-clay particles. More fungal PLFA-C was measured, however, in microaggregates compared with silt-and-clay. The lack of differences between the mol% within the microbial communities of the cropping systems and between the PLFA-C in the microaggregates and the silt-and-clay may have been due to (i) insufficient differences in quality between roots and residues and/or (ii) the high N availability in these N-fertilized cropping systems that augmented the abilities of the microbial communities to process a wide range of substrate qualities. The main implications of this study are that (i) the greater short-term microbial processing of root- than residue-C can be a mechanistic explanation for the higher relative retention of root- over residue-C, but microbial community composition did not influence long-term C sequestration trends in the three cropping systems and (ii) in spite of the similarity between the microbial community profiles of the microaggregates and the silt-and-clay, more C was processed in the microaggregates by fungi, suggesting that the microaggregate is a relatively unique microenvironment for fungal activity.

本研究将稳定同位素探测与磷脂脂肪酸分析 ( ¹³ C-PLFA) 结合起来，以描述微生物群落组成在根的短期加工（即 C 并入微生物生物量和/或 C 的沉积或呼吸）中的作用- 与传统（每年施用合成肥料）、低投入（交替年份施用合成肥料和覆盖作物）和有机（每年添加堆肥肥料和覆盖作物）中的残留碳和最终的长期碳封存相比玉米-番茄（Zea mays – Lycopersicum esculentum）种植系统。在玉米生长季节，我们将¹³ C 标记的毛野豌豆 ( Vicia dasycarpa ) 根和残留物追踪到从土壤微团聚体 (53–250 μm) 和淤泥和粘土 (<53 μm) 颗粒中提取的 PLFA 中。有机PLFA生物量最大（41.4 nmol g ^-1土壤），常规系统和低投入系统之间的相似（分别为31.0和30.1 nmol g ^-1土壤），其中革兰氏阳性细菌PLFA在微生物群落中占主导地位。所有系统。尽管来自根部的 PLFA-C 总量比来自残留物的 PLFA-C 总量多四倍多，但根部和残留物来源的 C 在微生物群落中的相对分布 (mol%) 在三种耕作系统中没有不同。此外，与粉土和粘土颗粒相比，PLFA 分布以及微团聚体 PLFA 中根和残渣 C 的掺入量都没有一致的不同。然而，与淤泥和粘土相比，在微团聚体中测量到了更多的真菌 PLFA-C。耕作系统的微生物群落内的 mol% 之间以及微团聚体中的 PLFA-C 与淤泥和粘土之间缺乏差异可能是由于 (i) 根和残留物之间的质量差异不足和/ (ii) 这些施氮肥的耕作系统中氮的利用率很高，增强了微生物群落处理各种基质质量的能力。这项研究的主要意义在于 (i) 根-C 的短期微生物处理作用比残渣-C 更大，这可以从机械角度解释根-C 相对于残渣-C 的相对保留率更高，但微生物群落组成并不影响三种耕作制度的长期碳封存趋势，以及（ii）尽管微团聚体和淤泥和粘土的微生物群落特征相似，但更多的碳在微团聚体中被真菌加工，这表明微团聚体是真菌活动相对独特的微环境。