Dynamics of residue 13C and 15N at various depths in diverse soils

Dr Monika Gorzelak1, Dr Ed Gregorich2, Dr Bobbi Helgason4, Dr Mike Beare3, Dr Denis Curtin3, Dr Ben Ellert1, Dr Henry Janzen1

1Agriculture And Agri-food Canada, Lethbridge, Canada, 2Agriculture and Agri-Food Canada, Ottawa, Canada, 3The New Zealand Institute of Plant and Food Research, Christchurch, New Zealand, 4University of Saskatchewan, Saskatoon, Canada

Plant litter decay and the persistence of its carbon (C) and nitrogen(N) crucially affect soil health and can impact soil carbon sequestration. We conducted a long-term experiment that asks: does the depth in soil profiles influence the processes and extent of residue turnover? Barley residue, highly enriched with 13C and 15N, was placed in mesh bags and buried at three depths in the soil profile (5-10 cm, 20-25 cm, 40-45 cm) at three sites with different climate and soil properties (Lincoln, New Zealand; Ottawa and Lethbridge Canada). The mesh bags were periodically retrieved over about a decade, and analyzed for 13C and 15N to determine recovery and also distribution in microbial phospholipid fatty acids (PLFA). At all sites and treatments, decay followed typical 1st-order kinetics, with high initial rates gradually diminishing over time. Decomposition was slower in the cold site (Lethbridge) than at other sites (Ottawa, Lincoln). Depth in soil profiles had no consistent effect on recovery of 13C, even though the residue was processed by different microbial communities, as determined by PLFA analysis. Dynamics of 15N showed patterns similar to those of 13C, although recovery was usually higher, indicating recycling of the N. The absence of a strong depth effect on litter turnover raises intriguing questions about opportunities for sequestering C in soil profiles, and invites further study of how microbes at depth process C and N inputs.


Monika Gorzelak is a new Soil Health Research Scientist with Agriculture and Agri-Food Canada specializing in soil microbial ecology. She has a PhD from UBC in Vancouver Canada with a thesis on communication between trees through mycorrhizal networks.

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