Effects of climate warming and elevated CO 2 on autotrophic nitrification and nitrifiers in dryland ecosystems

Abstract

a b s t r a c tGlobal climate change is predicted to enhance atmospheric temperature and CO 2 , with important consequences on biogeochemical nitrogen cycling in dryland ecosystems, which are highly vulnerable and characterized by extremely low nutrient availability. Belowground nitrification processes, predominantly mediated by ammonia-oxidizing archaea (AOA) and bacteria (AOB), are central to plant nitrogen availability and soil N 2 O emissions, but their responses to future climatic scenarios in drylands remain largely unknown. Here we investigated the impact of factorial combinations of elevated CO 2 (þ200 ppm) and elevated temperature (þ3 C) on dynamics of ammonia oxidizers and nitrification in three dryland soils planted with Eucalyptus tereticornis. Soil properties (including total carbon, H 2 O%, and nitrate) and potential nitrification rates were strongly impacted by elevated temperature after nine months, accompanied by significantly higher AOA abundance in two soils and a gradual decrease in AOB abundance under elevated temperature. DNA-stable isotope probing showed increased assimilation of 13 CO 2 by AOA, but not AOB, under warming, indicating that AOA were actively growing and utilizing the 13 CO 2 substrates, which was coupled with significantly higher net nitrogen mineralization and nitrification rates. High-throughput microarray analysis revealed temperature selections of particular AOA assemblages and a significant reduction in diversity and co-occurrence of the metabolically active AOA phylotypes. Although these responses were soil specific, structural equation modelling by compiling all the data together showed that warming had significant direct and indirect impacts on soil nitrification which were driven by changes in AOA community structure, but no obvious effects of elevated CO 2 could be identified. Our findings suggest that warming has stronger effects than elevated CO 2 on autotrophic nitrification, and AOA are more responsive to elevated temperature than AOB in the tested dryland ecosystems.

Microbial nitrous oxide emissions in dryland ecosystems: mechanisms, microbiome and mitigation

“…Therefore, the high efficiency of metabolism and strong ability to compete for substrates perfectly suit the oligotrophic lifestyle of AOA to thrive in drylands with a constantly low‐level energy supply (He et al ., ; Hu et al ., ). The majority of AOB, however, stay less active or dormant under dry conditions (Hu et al ., 2015b, 2016) and in nutrient‐poor environments (He et al ., ), thus presumably contributing less to N 2 O production in drylands. Although the number of studies is small, it appears that, apart from fungal denitrification, AOA ammonia oxidation may also account for a significantly large portion of dryland N 2 O production during the dry seasons (Fig.…”

“…Dryland‐specific predictions are not universal and readily available, but it has been reported that global warming can reduce the diversity and cover of lichen‐dominated biocrusts, and alter N transformation rates, inorganic N pools (Delgado‐Baquerizo et al ., ) and N 2 O emissions in drylands, and thus induces reinforcing (positive) or stabilizing (negative) feedbacks (Del Grosso and Parton, ). An increase in available N pools (Delgado‐Baquerizo et al ., ) as well as enhanced metabolic activity of N‐cycling microorganisms (Hu et al ., ) under climate warming may further contribute to increased dryland N 2 O emissions. In addition, it was found that the abundance and metabolic activity of AOA and AOB responded differently to warming, with increasing dominance of AOA in nitrification, and thus potentially increasing contribution to N 2 O production, under experimental warming within dryland forest (Hu et al ., ) and grassland soils (Tourna et al ., ).…”

Biochar reduces yield-scaled emissions of reactive nitrogen gases from vegetable soils across China

“…MBC was determined by substrate-induced respiration using gas chromatography (Anderson and Domsch 1978). PNR was measured using the chlorate inhibition soil-slurry method as previously described (Kurola et al, 2005) with modifications (Hu et al, 2016). DEA was quantified as described by Smith and Tiedje (1979).…”

Temporal changes of antibiotic-resistance genes and bacterial communities in two contrasting soils treated with cattle manure

“…Digests were incubated at 37 • C for 3 h, followed by 10 min at 95 • C to deactivate the restriction enzyme. Terminal restriction fragments (TRFs) were resolved on an ABI PRISM 3500 Genetic Analyzer (Applied Biosystems, CA, USA), and processed using Genemapper version 4.0 (Applied Biosystems) as described previously (Hu et al 2015(Hu et al , 2016. The relative fluorescence abundance of all TRFs was exported for downstream analysis.…”