Effects of aboveground grazing on coupling among nitrifier activity, abundance and community structure

Abstract

The influence of switches in grassland management to or from grazing on the dynamics of nitrifier activity, as well as the abundance of ammonia-oxidizing bacteria, AOB and ammonia-oxidizing archeae, AOA, was analyzed for two years after changing management. Additionally community structure of AOB was surveyed. Four treatments were compared in mesocosms: grazing on previously grazed grassland (G-G); no grazing on ungrazed grassland (U-U); grazing on ungrazed grassland (U-G) and cessation of grazing on grazed grassland (G-U). Nitrifier activity and abundance were always higher for G-G than U-U treatments and AOB community structure differed between these treatments. AOA abundance was in the same range as AOB abundance and followed the same trend. Grazing led to a change in AOB community structure within o5 months and a subsequent (5-12 months) increase in nitrifier activity and abundance. In contrast, cessation of grazing led to a decrease in nitrifier activity and abundance within o5 months and to a later (5-12 months) change in AOB community structure. Activity in G-U and U-G was similar to that in U-U and G-G, respectively, after 12 months. Sequence analysis of 16S rRNA gene clones showed that AOB retrieved from soils fell within the Nitrosospira lineage and percentages of AOB related to known Nitrosospira groups were affected by grazing. These results demonstrate that AOB and AOA respond quickly to changes in management. The selection of nitrifiers adapted to novel environmental conditions was a prerequisite for nitrification enhancement in U-G, whereas nitrification decrease in G-U was likely due to a partial starvation and decrease in the abundance of nitrifiers initially present. The results also suggest that taxonomic affiliation does not fully infer functional traits of AOB.

Effect of nitrogen fertilizer on nitrogen pools and soil communities under grazed pastures

“…The bacterial community structure (and nitrifier activity) can respond rapidly to changes in management, such as increased grazing and additions of animal urine (Le Roux et al 2008;Rooney & Clipson 2008;Singh et al 2009;Di et al 2010). The actinomycetes (a group of gram' bacteria) measured by PLFA were higher at HFC (P 00.01) and this is generally consistent with other studies showing that gram' bacteria often increase with increased intensity of grazing (Bardgett et al 1999;Klumpp et al 2009).…”

Bacteria, not archaea, restore nitrification in a zinc-contaminated soil

“…Our failure to detect a shift in the AOA community suggested the AOA community did not have the capacity to respond to Zn-induced stress over a 2-year time period. Similar to our results, changes of the numbers of AOB and AOA amoA gene copies, gene transcripts and/or amoA gene profiles suggested AOB dominated ammonia oxidation in an alkaline sandy loam soil under different long-term fertilization regimes , in grassland under different grazing managements (Le Roux et al 2008) and in long-term acidified soil samples . In contrast, data on the numbers of AOB and AOA amoA gene transcripts in soils incubated at different temperatures (Tourna et al, 2008) and in nitrogen fertilized paddy rhizosphere soils (Chen et al, 2008) suggest an AOA-dominated ammonia-oxidation process.…”

Agricultural Management and Labile Carbon Additions Affect Soil Microbial Community Structure and Interact with Carbon and Nitrogen Cycling

“…These observations are consistent with the model proposed for the soil microbial loop, in which microbial growth is matched by increased predation allowing rates of respiration and mineralization to increase without changes in the standing stock of microbial biomass [61][62][63][64][65][66]. Another potential explanation for increased N mineralization in organically managed soils is a change in the community composition of nitrifying organisms, since different groups of nitrifying bacteria display different nitrification kinetics [19,20,[67][68][69].…”