The influence of soil pH on denitrification: progress towards the understanding of this interaction over the last 50 years

Abstract

Summary Results from the pioneering research on the interactions between pH and denitrification in soil from the 1950s to the present are reviewed, the changing perceptions of this complex relationship are discussed, and the current status of the subject is assessed. Facets of this relationship that are analysed in detail include the direct or indirect influence of pH on overall denitrification rates in soils, changes in the composition of gaseous products that depend on pH, methods for measuring the process, the concept of an optimum pH for denitrification, and the adaptation of microbial denitrifying communities to acidic environments. The main conclusions to be drawn are as follows. Total gaseous emissions to the atmosphere (N2O, NO and N2) have repeatedly been shown to be less in acidic than in neutral or slightly alkaline soils. This may be attributable to smaller amounts of organic carbon and mineral nitrogen available to the denitrifying population under acid conditions rather than a direct effect of low pH on denitrification enzymes. Numerous laboratory and field studies have demonstrated that the ratio N2O:N2 is increased when the pH of soils is reduced. The relation between soil pH and potential denitrification as determined by various incubation methods remains unclear, results being influenced both by original conditions in soil samples and by unknown changes during incubation. The concept of an optimum pH for denitrification has been frequently proposed, but such a term has little or no meaning without reference to specific attributes of the process.

Spatial and temporal variability in CH4 and N2O fluxes from a Scottish ombrotrophic peatland: Implications for modelling and up-scaling

“…N 2 O emissions were negatively correlated (P < 0.1) with soil pH in both the full study period and the growing season 2006 models (Table 3a and b).The optimum pH from denitrifiers is often thought to be between approximately 6.5-8.0 (Knowles, 1981;Šimek and Cooper, 2002), therefore any increase above the mean catchment pH of 4.18 should theoretically increase N 2 O production. However the partitioning of N 2 O and N 2 is also influenced by pH with a higher proportion of N 2 O in more acid conditions (Šimek et al, 2002).…”

Redox potential (Eh) and pH as drivers of soil/plant/microorganism systems: a transdisciplinary overview pointing to integrative opportunities for agronomy

“…N 2 O emission is correlated with soil Eh (Kralova et al 1992;Masscheleyn et al 1993;Wlodarczyk et al 2003;Yu and Patrick 2003), and with soil pH as pH influences the three most important processes that generate N 2 O and N 2 : nitrification, denitrification, and dissimilatory NO 3 -reduction to NH 4 + (Simek and Cooper 2002). Eh and pH also interact in determining N 2 O and CH 4 emission: the Eh range with minimum N 2 O and CH 4 production shifts to lower values of the Eh scale when pH increases (Yu and Patrick 2003).…”

“…In soil science, for instance, despite the recognition of the importance of Eh, pH is often regarded as the master variable (Brady and Weil 2010;Simek and Cooper 2002). This is also the case in plant physiology (Rengel 2002).…”

Seasonal variability of denitrification efficiency in northern salt marshes: An example from the St. Lawrence Estuary

“…Results based on field and laboratory studies (Simek and Cooper, 2002) determinede that denitrification processes measured in cold salt marshes would not be a significant source of N 2 O. These authors showed that denitrification end products were mostly determined by sediment pH with low N 2 O/N 2 production ratios in more neutral sediment.…”