Nitrogen fertiliser rate affects the frequency of nitrate-dissimilating <i>Pseudomonas</i> spp. in the rhizosphere of <i>Lolium perenne</i> grown under elevated pCO₂ (Swiss FACE)

The effect of elevated pCO₂ (60 Pa) on the frequency of nitrate-dissimilating <i>Pseudomonas</i> (NDP) was investigated in the rhizosphere of fertilised <i>Lolium perenne</i> swards in the Swiss Free Air Carbon dioxide Enrichment (FACE) experiment. Numbers of cultivable root-associated <i>Pseudomonas</i> were greater under elevated (60 Pa) than under ambient (36 Pa) pCO₂ in both high and low N-fertilised swards. For both pCO₂ conditions, the NDP frequency decreased with closer root proximity to <i>L. perenne</i> roots in low fertilised swards. Anyway, in high N swards the NDP frequency was similar in root and soil fractions. Thus, N availability may be a major factor influencing NDP populations under elevated pCO₂, most likely due to increased competition for N between plant and nitrate-dissimilating bacteria.