Nitrification, denitrification, and related functional genes under elevated CO₂: A meta‐analysis in terrestrial ecosystems

Abstract

Global change may have profound effects on soil nitrogen (N) cycling that can induce positive feedback to climate change through increased nitrous oxide (N2O) emissions mediated by nitrification and denitrification. We conducted a meta‐analysis of the effects of elevated CO2 on nitrification and denitrification based on 879 observations from 58 publications and 46 independent elevated CO2 experiments in terrestrial ecosystems. We investigated the effects of elevated CO2 alone or combined with elevated temperature, increased precipitation, drought, and N addition. We assessed the response to elevated CO2 of gross and potential nitrification, potential denitrification, and abundances of related functional genes (archaeal amoA, bacterial amoA, nirK, nirS, and nosZ). Elevated CO2 increased potential nitrification (+28%) and the abundance of bacterial amoA functional gene (+62%) in cropland ecosystems. Elevated CO2 increased potential denitrification when combined with N addition and higher precipitation (+116%). Elevated CO2 also increased the abundance of nirK (+25%) and nirS (+27%) functional genes in terrestrial ecosystems and of nosZ (+32%) functional gene in cropland ecosystems. The increase in the abundance of nosZ under elevated CO2 was larger at elevated temperature and high N (+62%). Four out of 14 two‐way interactions tested between elevated CO2 and elevated temperature, elevated CO2 and increased precipitation, and elevated CO2 and N addition were marginally significant and mostly synergistic. The effects of elevated CO2 on potential nitrification and abundances of bacterial amoA and nirS functional genes increased with mean annual temperature and mean annual precipitation. Our meta‐analysis thus suggests that warming and increased precipitation in large areas of the world could reinforce positive responses of nitrification and denitrification to elevated CO2 and urges the need for more investigations in the tropical zone and on interactive effects among multiple global change factors, as we may largely underestimate the effects of global change on soil N2O emissions.

Warming-Induced Stimulation of Soil N2O Emissions Counteracted by Elevated CO2 from Nine-Year Agroecosystem Temperature and Free Air Carbon Dioxide Enrichment

“…Such results are in line with a previous study that found that CO 2 enrichment significantly decreased N 2 O emissions by 22% in global paddy soils 60 but contrasted with most meta-analysis studies reporting a stimulation of soil N 2 O emissions by CO 2 enrichment in terrestrial ecosystems. 25,61,62 The effect of CO 2 enrichment on soil N 2 O emissions may vary depending on the ecosystem. For instance, elevated CO 2 caused a nonsignificant increase in soil N 2 O emissions in terrestrial ecosystems but a significant increase in soil N 2 O emissions in fertilized upland soils and in natural wetlands.…”

“…Previous studies on natural and seminatural ecosystems like grasslands have indicated that elevated CO 2 affects N 2 O emissions depending on their effects on denitrification-derived N 2 O emission. ,, Under warming, nonsignificant increases in nitrification-derived and total N 2 O emissions have been reported in a Tibetan alpine meadow . However, such results cannot be extrapolated to agricultural ecosystems with large N fertilizer inputs and highly anthropogenic disturbances because of the different responses to soil properties associated with N transformations to elevated CO 2 and warming under more intensive agriculture. ,, For example, the response of soil inorganic N to warming is significantly higher in cropland than in grassland and shrubland . Complicating things further, these responses to multiple factors might not be predicted by simple linear extrapolations from single-factor studies because multifactor responses are frequently nonadditive and even counteractive. ,,, For instance, warming notably decreased soil organic matter at ambient CO 2 conditions while leading to a negligible effects at elevated CO 2 level, suggesting a significant interaction between elevated CO 2 and warming .…”

“…15 However, such results cannot be extrapolated to agricultural ecosystems with large N fertilizer inputs and highly anthropogenic disturbances because of the different responses to soil properties associated with N transformations to elevated CO 2 and warming under more intensive agriculture. 8,24,25 For example, the response of soil inorganic N to warming is significantly higher in cropland than in grassland and shrubland. 24 Complicating things further, these responses to multiple factors might not be predicted by simple linear extrapolations from single-factor studies because multifactor responses are frequently nonadditive and even counteractive.…”

Cultivation increased soil potential denitrification rates by modifying denitrifier communities in desert‐oasis ecotone

“…Denitrification (NO 3 − ‐N → NO 2 − ‐N → NO→N 2 O → N 2 ), a key link in the N cycle, is an important pathway resulting in the loss of available N in soils (Attard et al, 2011; Lan et al, 2023; Z. Li, Tang, et al, 2021; Z. Li, Tiang, et al, 2021). Nitrite reductase‐mediated reduction of NO 2 ‐ to NO is the central step in denitrification because dissolved N becomes gaseous N for the first time (Gineyts & Niboyet, 2023; Yang et al, 2017; Yin et al, 2014). Currently, nitrite reductase marker genes ( nirK and nirS ) are routinely used, enabling us to reveal the abundance and structure of denitrifying microbes in soil samples.…”

“…Li, Tiang, et al, 2021). Nitrite reductase-mediated reduction of NO 2 -to NO is the central step in denitrification because dissolved N becomes gaseous N for the first time (Gineyts & Niboyet, 2023;Yang et al, 2017;Yin et al, 2014). Currently, nitrite reductase marker genes (nirK and nirS) are routinely used, enabling us to reveal the abundance and structure of denitrifying microbes in soil samples.…”