科研之友
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摘要
Root-derived carbon (C) is preferentially retained in soil compared to aboveground C inputs. Microbial communities in the rhizosphere are crucial to nutrient and organic matter cycling within agroecosystems. The overall aim of this study was to investigate the impacts of crop management on microbial community structure and processing of rhizodeposit-C within microenvironments of two soil zones, the rhizosphere versus non-rhizosphere. New root-C (C-new) from C-13-labeled hairy vetch (Vicia dasycarpa) plants were traced into phospholipid fatty acids (PLFA) within microaggregate (53-250 mu m) and silt-and-clay (< 53 mu m) microenvironments in rhizosphere and non-rhizosphere soil during the cover crop growing season in long-term 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 systems (Zea mays L.- Lycopersicum esculentum L.). Among the three cropping systems, the composition of the microbial communities processing root-derived C were similar, which implied that the cropping systems maintained diverse microbial communities that were capable of utilizing similar C substrates despite receiving different long-term nutrient inputs. Relative distributions of root-derived PLFA-C (C-13 mol%) in the rhizosphere and non-rhizosphere were not significantly different, thereby suggesting that the structure of the microbial community utilizing new root-C in the rhizosphere- and non-rhizosphere microenvironments were similar. However, total PLFA biomass was four times greater, and root-derived PLFA-C in both soil microenvironments were approximately 10 times greater in the rhizosphere than in the non-rhizosphere. Although no microbial group dominated the processing of C-new in the microenvironments of the rhizosphere and non-rhizosphere, we found that the microbial community of the silt-and-clay in the rhizosphere played a different role in the cycling of C-new compared to communities in the rhizosphere microaggregates and those in the silt-and-clay and microaggregates of the non-rhizosphere. Our results confirm that rhizodeposition plays an important role in the greater contribution of root-C than residue-C to SOM stabilization. This study also showed that microbial communities assimilating rhizodeposit-C are sensitive to their microenvironment (i.e., microaggregates versus silt-and-clay particles); nevertheless, differences in long-term crop management did not lead to differences in the capacity of the microbial communities to utilize active cover crop root-C substrates.
- 出版日期2012-7
