Winter expression of soil nitrogen cycle genes in agricultural soils representing the Boreal Atlantic Maritime climate

Valdez, Victor Pablo (2019) Winter expression of soil nitrogen cycle genes in agricultural soils representing the Boreal Atlantic Maritime climate. Masters thesis, Memorial University of Newfoundland.

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Abstract

The expression of the soil nitrogen-fixing (nifH), ammonia oxidizing (archaea and bacteria amoA) and denitrifying (narG, napA, nirK, nirS, and nosZ1) genes are commonly used as indicators for these processes during the non-growing season. This study quantified the transcript abundance profiles of these genes by cDNA for Droplet Digital PCR in soils for the control (native vegetation) and four, regionally relevant crop production systems in Newfoundland. Soil parameters analysed were pH, total carbon, NH4+-N, NO3--N, and water-filled pore space. All genes quantified were expressed in winter suggesting that microorganisms were responding to minute changes in soil parameters; and that N-fixation and (de)-nitrification were co-occurring. Snowpack accumulation led to an increase in all transcript abundance profiles while pure alfalfa stands using mineral fertilizers had the lowest transcript abundance profiles. NO₃⁻-N and pH were negatively correlated to nifH gene expression, suggesting the latter is likely downregulated to balance growth in acidic soil conditions.

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