A 3-year exposure to CO2 and O3 induced minor changes in soil N cycling in a meadow ecosystem

Abstract

We investigated the individual and interactive effects of moderately elevated CO 2 (ambient air + 100 ppm) and/or O 3 (40-50 ppb) on soil N cycling and microbial biomass N in a 3-year open-top chamber experiment conducted in meadow mesocosms. The results show that elevated O 3 decreased the concentrations of mineral N and NH 4 + -N in the mesocosm soil in the last growing season (2004). Total N, NO 3 --N, microbial biomass N, decomposition rate, potential nitrification and denitrification were not affected by elevated O 3 and/or CO 2 . It is thus concluded that the proposed future ambient O 3 and CO 2 levels, such as used in this experiment, may not induce major changes in the belowground N processes in N-poor northern European hay meadow ecosystems.

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.…”

“…Other possible explanations for decreased NH 4 concentrations may include increased plant uptake of N, increased microbial biomass (Kanerva et al, 2006;Bassin et al, 2015) or decreased N 2 fixation rate (Pausch et al, 1996;Li et al, 2013). Increased N concentrations of leaves in response to elevated O 3 have been observed in trees and grasslands (Wittig et al, 2009;Bassin et al, 2015), but this has rather been attributed to increased retranslocation of N after early senescence of part of the leaves, reduced plant size (Wittig et al, 2009) and reduced N resorption from senescing leaves (Uddling et al, 2006).…”

“…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.…”

Effects of elevated CO2 and O3 on N-cycling and N2O emissions: a short-term laboratory assessment

“…Studies on the effect of elevated O 3 (eO 3 ) on N 2 O emissions are scarcer than studies on the effect of eCO 2 (Kanerva et al 2006;Kanerva et al 2007). Decreases in N-mineralization (Holmes et al 2006;Holmes et al 2003), microbial biomass N (Holmes et al 2003;Kanerva et al 2006), potential denitrification (Kanerva et al 2006) and N 2 O flux rate (Kanerva et al 2007) have been attributed to decreased belowground biomass production and associated reduction of substrate input in the soil.…”