123-17 Microbial Decomposition of Incorporated and Surface-Applied Barley Residue In Humid and Semi-Arid Climates Using 13 C-Labelled PLFA.



Monday, October 17, 2011
Henry Gonzalez Convention Center, Hall C, Street Level

Roberta Helgason, 51 Campus Drive, Agriculture & Agri-Food Canada, Saskatoon, SK, CANADA, Edward Gregorich, Agriculture and Agri-Food Canada, Ottawa, ON, Canada, Benjamin Ellert, Agriculture and Agri-Food Canada, Lethbridge, AB, Canada, Henry Janzen, Agriculture and Agri-Food Canada, Lethbridge Research Centre, Lethbridge, AB, Canada and Richard Dick, 406C Kottman Hall, 2021 Coffey Road, The Ohio State University, Columbus, OH

Decomposition of crop residues provides the primary source of new C in agricultural soil, and understanding residue C decomposition in different soils is important for developing and promoting practices that best sustain a soil's productive capacity. Stable isotope probing of the microbial community using 13C is a powerful tool for tracking residue C as it flows through the microbial biomass. As part of a larger long-term study that investigates the rate and pathways of litter decay, we studied the incorporation of 13C from barley residue into the microbial biomass using phospholipid fatty acid analysis (PLFA).

Study sites under contrasting climatic conditions were located at Ottawa, ON (humid) and Lethbridge, AB (semi-arid), Canada. In situ microcosms were established in which labelled residues were either surface-applied or incorporated into the soil (10 cm deep). At approximately 0.5, 1 and 2 yr, microcosms were destructively sampled, divided into two 5-cm increments, and analyzed for 13C enrichment of microbial PLFAs. At Ottawa about twice as much 13C was detected in the microbial PLFAs where residue was incorporated vs. surface-applied after 0.5 yr but this difference disappeared after 1 yr. At Lethbridge approximately half as much label was recovered in the PLFAs from the surface-applied vs. incorporated residue treatment after 2 yr and a greater overall proportion of the residue 13C was detected in the microbial biomass at Lethbridge compared to Ottawa.

After about 1 yr, the proportion of residue-derived C that was assimilated decreased for fungi but increased for bacteria and was not affected by residue placement. Overall, the fungal biomass was more heavily labeled with 13C than the bacterial biomass. Residue placement affected microbial community structure even after 2 yr, and this effect was stronger under more arid conditions.

See more from this Division: S03 Soil Biology & Biochemistry
See more from this Session: Microbe, Plant , and Soil Interactions (Includes Graduate Student Poster Competition)