Soil nitrogen transformations under elevated atmospheric CO2 and O3 during the soybean growing season

Abstract

We investigated the influence of elevated CO2 and O3 on soil N cycling within the soybean growing season and across soil environments (i.e., rhizosphere and bulk soil) at the Soybean Free Air Concentration Enrichment (SoyFACE) experiment in Illinois, USA. Elevated O3 decreased soil mineral N likely through a reduction in plant material input and increased denitrification, which was evidenced by the greater abundance of the denitrifier gene nosZ. Elevated CO2 did not alter the parameters evaluated and both elevated CO2 and O3 showed no interactive effects on nitrifier and denitrifier abundance, nor on total and mineral N concentrations. These results indicate that elevated CO2 may have limited effects on N transformations in soybean agroecosystems. However, elevated O3 can lead to a decrease in soil N availability in both bulk and rhizosphere soils, and this likely also affects ecosystem productivity by reducing the mineralization rates of plant-derived residues.

How does elevated ozone reduce methane emissions from peatlands?

“…Most studies attributed reduced soil NH 4 concentrations or changes in soil N concentration or microbial biomass N in response to elevated O 3 to reduced below-ground C inputs, reduced litter quality (Kanerva et al, 2006;Bhatia et al, 2011;Pereira et al, 2011) or higher nitrification and denitrification rates (Li et al, 2010;Pereira et al, 2011). We have no evidence of such changes in C inputs in elevated O 3 in our study.…”

“…emissions, it remains likely that changes in the methanogenic and/or methanotrophic communities were the key underlying explanation. (Bhatia et al, 2011), meadows (Kanerva et al, 2006) and soybean crops (Pereira et al, 2011). A positive link between soil inorganic N availability and methanogenic activity is plausible, and CH 4 emission in paddy soils has been positively correlated to levels of soil mineralisable N (e.g.…”

“…This may be through reduced litter quantity or quality, although effects of O 3 on nitrification, denitrification, microbial biomass and plant uptake of N have also been reported (Wittig et al, 2009;Li et al 2010;Bhatia et al, 2011;Pereira et al, 2011;Bassin et al, 2015). In nitrogen (N) poor systems such as peatlands, reduced below-ground allocation of N could cause reduced activity of heterotrophic soil microorganisms, such as methanogens (Kanerva et al, 2007).…”

“…In nitrogen (N) poor systems such as peatlands, reduced below-ground allocation of N could cause reduced activity of heterotrophic soil microorganisms, such as methanogens (Kanerva et al, 2007). However, lower availability of ammonium (NH 4 ), the dominant form of inorganic N in peatlands, could also promote methanotrophic activity (Keller et al, 2006), and O 3 has been reported to reduce soil NH 4 concentrations in meadows (Kanerva et al (2006) and soybean crops (Pereira et al, 2011). A direct adverse effect of O 3 on methanotrophs in the top layers of the moss cover of peatlands may also play a role, with Raghoebarsing et al (2005) showing CH 4 consumption by Sphagnum plants through partly-endophytic methanotrophs in hyaline cells and on stem leaves.…”

Distinct responses of soil microbial communities to elevated CO2 and O3 in a soybean agro-ecosystem

“…The 32-h SoyFACE experiment was established on a farmland that had been cultivated with an annual rotation of soybean, Glycine max (L.) Merr. and corn, Zea mays L. for more than 25 years, and the soil at the site is a Drummer fine-silty, mixed, mesic Typic Endoaquoll, typical of wet, dark-colored 'prairie soils' in northern and central Illinois (Pujol Pereira et al, 2011). More soil background properties, including soil pH, moisture, Bray P, K, Ca and Mg were previously documented (Peralta and Wander, 2008).…”