Impacts of nitrogen application rates on the activity and diversity of denitrifying bacteria in the Broadbalk Wheat Experiment

Abstract

Bacterial denitrification results in the loss of fertilizer nitrogen and greenhouse gas emissions as nitrous oxides, but ecological factors in soil influencing denitrifier communities are not well understood, impeding the potential for mitigation by land management. Communities vary in the relative abundance of the alternative dissimilatory nitrite reductase genes nirK and nirS , and the nitrous oxide reductase gene nosZ ; however, the significance for nitrous oxide emissions is unclear. We assessed the influence of different long-term fertilization and cultivation treatments in a 160-year-old field experiment, comparing the potential for denitrification by soil samples with the size and diversity of their denitrifier communities. Denitrification potential was much higher in soil from an area left to develop from arable into woodland than from a farmyard manure-fertilized arable treatment, which in turn was significantly higher than inorganic nitrogen-fertilized and unfertilized arable plots. This correlated with abundance of nirK but not nirS, the least abundant of the genes tested in all soils, showing an inverse relationship with nirK . Most genetic variation was seen in nirK , where sequences resolved into separate groups according to soil treatment. We conclude that bacteria containing nirK are most probably responsible for the increased denitrification potential associated with nitrogen and organic carbon in this soil.

Nitrogen cycle bacteria in soils of organically and conventionally managed crop rotations

“…Nitrate reduction by denitrification is of great importance because it can lead to considerable nitrogen losses in agriculture and emissions of greenhouse gases (Cheneby et al, 2009). In general, activity of this process increases with soil temperature and moisture and is strongly dependent on soil physiochemical properties especially on soil organic carbon content (Szukics et al, 2010;Clark et al, 2012;Miller et al, 2012). According to the findings of Cheneby et al (2009), nitrate reduction activity was stimulated by combined organic and mineral fertilization but not by organic fertilization alone.…”

“…Denitrifying bacteria are more numerous than any other functional groups involved in the nitrogen cycle (Clark et al, 2012). Nitrate reduction by denitrification is of great importance because it can lead to considerable nitrogen losses in agriculture and emissions of greenhouse gases (Cheneby et al, 2009).…”

Simulating soil carbon sequestration from long term fertilizer and manure additions under continuous wheat using the DailyDayCent model

“…Overall, a good agreement was observed between modelled and measured yield, except for the plot with no nutrient input (control plot). In spite of no fertilizer application, a yield increase in the control plot has been observed (Clark et al 2012;Powlson et al 2014), which, it has been proposed, could be due to atmospheric N deposition of around 35-45 kg N ha -1 a -1 . Including N deposition in DDC tends to reduce the gap between modelled and measured yield, but could not explain the entire gap between modelled results and observations.…”

Soil resilience and recovery: rapid community responses to management changes

“…Due to practical limitations, not all parameters could be measured each year and we used our previous experience (Hirsch et al 2009;Clark et al 2012) to plan sampling to cover the most relevant periods of change. A randomised sampling grid was designed at the outset of the conversion to provide 160 sampling areas of 0.25 m 2 to ensure that no part of each plot was sampled more than once and different assays did not interfere.…”

“…DNA samples and PCR results failing to meet our quality criteria were discarded: a full description of the primers, PCR conditions and quality controls has been described previously (Cardenas et al 2013;Clark et al 2012) and is provided in the Supplementary Information. We did not quantify archaeal 16S rRNA genes: previous results indicated that they were 100-times less frequent than bacteria in our soils and the vast majority were ammonia oxidizers, so would be enumerated by the primers for archaeal amoA (Zhalnina et al 2013).…”