Agricultural Management and Labile Carbon Additions Affect Soil Microbial Community Structure and Interact with Carbon and Nitrogen Cycling

• Published in: Microbial ecology 2013-07, Vol.66 (1), p.158-170
• Main Authors: Berthrong, Sean T., Buckley, Daniel H., Drinkwater, Laurie E.
• Format: Article
• Language: English
• Subjects: Agricultural ecosystems; Agricultural management; Agricultural soils; Agriculture; Agriculture - methods; Bacteria; Bacteria - classification; Bacteria - genetics; Bacteria - isolation & purification; Bacteria - metabolism; Biological and medical sciences; Biomedical and Life Sciences; Carbon - analysis; Carbon - metabolism; Carbon Cycle; Community composition; Community structure; Ecology; Ecosystem; Farming; Forest soils; Fundamental and applied biological sciences. Psychology; Geoecology/Natural Processes; Life Sciences; Microbial activity; Microbial Ecology; Microbiology; Mineralization; Nature Conservation; Nitrogen - analysis; Nitrogen - metabolism; Nitrogen Cycle; Organic soils; Respiration; Soil - chemistry; Soil bacteria; Soil biochemistry; Soil composition; Soil fungi; Soil management; SOIL MICROBIOLOGY; Soil microorganisms; Soil moisture; Soil samples; Water Quality/Water Pollution
• ISSN: 0095-3628; 1432-184X
• DOI: 10.1007/s00248-013-0225-0

We investigated how conversion from conventional agriculture to organic management affected the structure and biogeochemical function of soil microbial communities. We hypothesized the following. (1) Changing agricultural management practices will alter soil microbial community structure driven by increasing microbial diversity in organic management. (2) Organically managed soil microbial communities will mineralize more N and will also mineralize more N in response to substrate addition than conventionally managed soil communities. (3) Microbial communities under organic management will be more efficient and respire less added C. Soils from organically and conventionally managed agroecosystems were incubated with and without glucose ( 13 C) additions at constant soil moisture. We extracted soil genomic DNA before and after incubation for TRFLP community fingerprinting of soil bacteria and fungi. We measured soil C and N pools before and after incubation, and we tracked total C respired and N mineralized at several points during the incubation. Twenty years of organic management altered soil bacterial and fungal community structure compared to continuous conventional management with the bacterial differences caused primarily by a large increase in diversity. Organically managed soils mineralized twice as much NO 3 — as conventionally managed ones (44 vs. 23 μg N/g soil, respectively) and increased mineralization when labile C was added. There was no difference in respiration, but organically managed soils had larger pools of C suggesting greater efficiency in terms of respiration per unit soil C. These results indicate that the organic management induced a change in community composition resulting in a more diverse community with enhanced activity towards labile substrates and greater capacity to mineralize N.