Dynamics of nitrifying activities, denitrifying activities and nitrogen in grassland mesocosms as altered by elevated CO₂

Abstract

Summary• The objective of this study was to better identify the mechanisms by which elevated CO 2 ( c . 665 µmol mol − 1 ) alters soil nitrifying and denitrifying enzyme activity (NEA and DEA), and the dynamics of plant and microbial N pools.• We measured the effects of elevated CO 2 on plant biomass and N, soil microbial biomass N, soil ammonium and nitrate concentrations, NEA and DEA in monospecific grassland mesocosms ( Holcus lanatus and Festuca rubra ) grown for 15 months in reconstituted grassland soil.• NEA strongly decreased at elevated CO 2 in the Holcus mesocosms, but was not affected in Festuca systems. DEA was less sensitive to elevated CO 2 than NEA. In Holcus mesocosms, microbial N showed an initial growth phase that appeared to limit plant N acquisition, but was only transient.• CO 2 -induced changes in NEA and DEA were best explained by factors that could reduce soil [O 2 ] (increased soil water content and organic C). Elevated CO 2 may increase microbial immobilisation in highly disturbed systems, this effect weakening as the system gets closer to equilibrium.

Multifactor controls on terrestrial N<sub>2</sub>O flux over North America from 1979 through 2010

“…If no progressive N limitation occurs under elevated CO 2 , enhanced N 2 O emission will be observed. As the theory of progressive N limitation predicts , rising atmospheric CO 2 could lead to low N availability in soil and thus lead to low N 2 O emission (Kettunen et al, 2005;Barnard et al, 2004). In this study, the elevated atmospheric CO 2 substantially decreased the N 2 O emission from terrestrial ecosystem over North America, which is due to the N limitation for major biomes throughout the entire North America (Vitousek and Farrington, 1997;Aber and Melillo, 2001).…”

Short-Term Uptake of 15N by a Grass and Soil Micro-Organisms after Long-Term Exposure to Elevated CO2

“…Although there are records of increased plant N uptake at elevated CO 2 , findings are not consistent (see review by Bassirirad, 2000). Barnard et al (2004b) measured the dynamics of plant N content and microbial biomass N in mesocosms of Holcus lanatus exposed to elevated atmospheric CO 2 over a period of 15 months. Plant N-limitation was observed at elevated CO 2 in the early stage of the experiment, while soil microbial biomass N increased.…”

The phylogenetic composition and structure of soil microbial communities shifts in response to elevated carbon dioxide

“…Conventional molecular biology approaches have demonstrated that soil microbial diversity generally increased (Mitchell et al, 2003;Janus et al, 2005;Sonnemann and Wolters, 2005;Jossi et al, 2006;Lesaulnier et al, 2008), decreased (Horz et al, 2004) or remained unchanged (Barnard et al, 2004;Ebersberger et al, 2004;Loy et al, 2004;Chung et al, 2006;Gruter et al, 2006;Lipson et al, 2006;Drigo et al, 2007Drigo et al, , 2009Austin et al, 2009;Ge et al, 2010) in response to eCO 2 . The apparent discrepancy of microbial responses to eCO 2 could be partially due to real differences among various ecosystems, but could also be due to differences in the methodologies used, such as terminal restriction-fragment length polymorphism, denaturing gradient gel electrophoresis, 16S rRNA-based sequencing, enzyme activities and phospholipid fatty acids.…”