Short-term response of nitrifier communities and potential nitrification activity to elevated CO2 and temperature interaction in a Chinese paddy field

• Elevated CO2 significantly increased both AOA and AOB abundance.
• The increased AOA and AOB abundances under CE were mitigated by warming.
• Warming alone did not affect the abundance and structure of AOA or AOB.
• Elevated CO2 and warming significantly increased PNR.

While microbial nitrogen transformations in terrestrial ecosystems are known to be affected by global climate change, changes in abundance and composition of mediating microorganisms in agricultural soils under climate change have not yet been well characterized. Here, using well-established molecular fingerprinting techniques and biochemical assays, we tried to analyze changes in nitrifier abundance, composition and activity in the rhizosphere under simultaneously elevated atmospheric CO2 and temperature conditions in a Chinese paddy field. Abundance, rather than community composition of ammonia oxidizing archaea and bacteria (AOA and AOB) responded to the climate change treatments, and the effect was greater on the heading and ripening stages (36–52%) than on the tillering stage (8–26%). Elevated atmospheric CO2 significantly increased AOA and AOB abundance at the heading and ripening stages. Treatment of WA (warming of canopy air) alone did not affect the abundance or community structure of AOA or AOB in the rice rhizosphere at any growth stage. The simultaneous application of CO2 enrichment and warming affected ammonia oxidizer communities differently than independent application of CO2 enrichment or warming, with warming negating the stimulating effect of CO2 enrichment. Phylogenic analysis indicated that all AOA clones fell within the soil and sediment lineage while all AOB clones were classified as Nitrosospira. Although no changes to soil NH4+ or NO3− contents were found, potential nitrification rate generally increased under the treatments with elevated CO2 at all rice growth stages. This could imply a complexity of the joint effect by elevated CO2 on soil properties, plant N uptake and microbial growth. These results suggest that impacts of climate change on N transformation in the rice paddy occur through interactions between effects of climate change on ammonia oxidizer communities and soil properties. Further studies would be required on multiple effects by simulated climate changes on soil properties, N transformations and microbial communities, for a sound understanding of potential changes in N cycling and rice productivity under global climate change.