Several components of global change alter nitrifying and denitrifying activities in an annual grassland

Abstract

Summary1. The effects of global change on below-ground processes of the nitrogen (N) cycle have repercussions for plant communities, productivity and trace gas effluxes. However, the interacting effects of different components of global change on nitrification or denitrification have rarely been studied in situ. 2. We measured responses of nitrifying enzyme activity (NEA) and denitrifying enzyme activity (DEA) to over 4 years of exposure to several components of global change and their interaction (increased atmospheric CO 2 concentration, temperature, precipitation and N addition) at peak biomass period in an annual grassland ecosystem. In order to provide insight into the mechanisms controlling the response of NEA and DEA to global change, we examined the relationships between these activities and soil moisture, microbial biomass C and N, and soil extractable N. 3. Across all treatment combinations, NEA was decreased by elevated CO 2 and increased by N addition. While elevated CO 2 had no effect on NEA when not combined with other treatments, it suppressed the positive effect of N addition on NEA in all the treatments that included N addition. We found a significant CO 2 -N interaction for DEA, with a positive effect of elevated CO 2 on DEA only in the treatments that included N addition, suggesting that N limitation of denitrifiers may have occurred in our system. Soil water content, extractable N concentrations and their interaction explained 74% of the variation in DEA. 4. Our results show that the potentially large and interacting effects of different components of global change should be considered in predicting below-ground N responses of Mediterranean grasslands to future climate changes.

Experimentally Simulated Global Warming and Nitrogen Enrichment Effects on Microbial Litter Decomposers in a Marsh

“…One of the clearest effects observed in our experiment was a shift in bacterial communities in response to simulated climate warming. Although published evidence on microbial responses to experimental warming under field conditions is scarce (4,30), observational data suggest that microbial communities can be greatly influenced by temperature regimes. For example, decreasing bacterial diversity was found along a temperature gradient in an artificially aerated lagoon (50), and soil bacterial communities differed along a thermal gradient (35 to 65°C) resulting from recent geothermal activity in Yellowstone National Park, with apparently less complex communities in heated than in geothermally unaffected soils (44).…”

Testing interactive effects of global environmental changes on soil nitrogen cycling

“…Warming generally increased net or gross N mineralization and immobilization rates (Rustad et al 2001, Shaw andHarte 2001), while the response of nitrification to increased temperature was highly variable, and the response of denitrification was generally non-significant (Barnard et al 2005). Changes in precipitation regimes, through changes in soil moisture, significantly altered rates of N cycling processes in field studies (Barnard et al 2006, Dijkstra et al 2010, Larsen et al 2010: in particular, increased soil moisture can result in enhanced N mineralization, N immobilization, and nitrification rates under water-limiting conditions (Jamieson et al 1999, Avrahami and Bohannan 2007, Dijkstra et al 2010, or in increased denitrification rates by enhancing anaerobic conditions (Barnard et al 2006). Finally, enhanced N deposition increased gross and potential N mineralization rates through increases in primary productivity and decreases in C/N ratio of the organic matter (Booth et al 2005, Vourtilis et al 2007) and enhanced gross and potential nitrification and denitrification rates through increases in soil inorganic N availability (Barnard et al 2005).…”

Ectomycorrhizal communities in a Mediterranean forest ecosystem dominated by Quercus ilex: seasonal dynamics and response to drought in the surface organic horizon

“…The effects of longer and more severe drought on soil biota are still poorly investigated. From an ecological point of view, a decrease in precipitation may reduce soil wetness (Limousin et al 2009), decrease soil carbon exchange (Misson et al 2010) and affect major soil enzymatic activities with consequences for phosphorus, carbon and nitrogen turnover (Barnard et al 2006;Sardans and Penuelas 2005).…”