Nitrogen cycling genes in a long-term land-use converted boreal land in Newfoundland, Canada

Nitrogen cycling genes in a long-term land-use converted boreal land in Newfoundland,
Canada
Victor Pablo Valdez, Abiraami Ramasami, Vanessa Kavanagh, David Burton, Linda Jewell,
David McKenzie, Adrian Unc
vv3755@mun.ca
In Newfoundland, Canada, the productivity of agricultural land converted from boreal forest is
sustained by additions of significant amounts of mineral and organic fertilizers, and management
of pH through addition of alkaline amendments. The efficiency of fertilization is determined by
the efficiency of the soil microbial community. This study examined the impacts of long-term
management (≈70 years) on the soil (N)itrogen-cycling potential and gene profile in a potatowheat
farm field in Cormack, Newfoundland. The distribution of ammonia oxidation (Cren-,
Arch-, bacterial- amoA) and denitrification (narG, napA, nirK, nirS, nosZ1) genes were
evaluated on transects across the field’s boundaries. Gradient sample points were outside (-3m, -
1m) and inside (1m, 3m, 5m) the farmed plot. Triplicate soil samples were collected at 0-10 and
10-20 cm depths along gradients at four sites. Results are contextualized by soil pH, organic
matter, total carbon, available and total phosphorous, total- N, mineralizable-N, and C:N, N:P,
and C:P ratios. Sampling was carried out at the end of August. N-cycle genes were quantified by
digital PCR. Soil physicochemical parameters were measured via standard soil analytical
methods. Multidimensional statistics were employed to explore the (a)biotic triggers for the
diversity of N-cycle genes, while the most informative models were identified via Akaike’s
Information Criterion. Diversity of abiotic and biotic parameters were linked to site and gradient
location. For 0-10 cm, models confirmed varying levels of correlation between the abundance of
each gene, the spatial variables, and abundance of other genes. For 10-20 cm, the associations
between genes were more pronounced, with a lower significance attached to spatial variables.
Thus, management effects are less pronounced for the deeper soil layer. These results suggest
that management affects, as well as a relationship between, the abundance profiles of soil
denitrifiers and nitrifiers.