Testing interactive effects of global environmental changes on soil nitrogen cycling

Abstract

Abstract. Responses of soil nitrogen (N) cycling to simultaneous and potentially interacting global environmental changes are uncertain. Here, we investigated the combined effects of elevated CO 2 , warming, increased precipitation and enhanced N supply on soil N cycling in an annual grassland ecosystem as part of the Jasper Ridge Global Change Experiment (CA, USA). This field experiment included four treatments-CO 2 , temperature, precipitation, nitrogen-with two levels per treatment (ambient and elevated), and all their factorial combinations replicated six times. We collected soil samples after 7 and 8 years of treatments, and measured gross rates of N mineralization, N immobilization and nitrification, along with potential rates of ammonia oxidation, nitrite oxidation and denitrification. We also determined the main drivers of these microbial activities (soil ammonium and nitrate concentrations, soil moisture, soil temperature, soil pH, and soil CO 2 efflux, as an indicator of soil heterotrophic activity). We found that gross N mineralization responded to the interactive effects of the CO 2 , precipitation and N treatments: N addition increased gross N mineralization when CO 2 and precipitation were either both at ambient or both at elevated levels. However, we found limited evidence for interactions among elevated CO 2 , warming, increased precipitation, and enhanced N supply on the other N cycling processes examined: statistically significant interactions, when found, tended not to persist across multiple dates. Soil N cycling responded mainly to single-factor effects: long-term N addition increased gross N immobilization, potential ammonia oxidation and potential denitrification, while increased precipitation depressed potential nitrite oxidation and increased potential ammonia oxidation and potential denitrification. In contrast, elevated CO 2 and modest warming did not significantly affect any of these microbial N transformations. These findings suggest that global change effects on soil N cycling are primarily additive, and therefore generally predictable from single factor studies.

Climate Change Predicted to Negatively Influence Surface Soil Organic Matter of Dryland Cropping Systems in the Inland Pacific Northwest, USA

“…In agreement with our results, Colman and Schimel (2013) concluded that the direct drivers of N mineralization were soil C and N as well as clay content and that precipitation drives N mineralization indirectly through its influence on soil C and N content. Regarding PDR, Niboyet et al (2011) found that experimentally increasing precipitation 50% for 8 years resulted in a 22% increase in PDR, in agreement with the positive correlation of PDR with MAP found in our study. Niboyet et al (2011) did not, however, detect sensitivity of PDR to warming of 1 • C for 8 years.…”

“…Regarding PDR, Niboyet et al (2011) found that experimentally increasing precipitation 50% for 8 years resulted in a 22% increase in PDR, in agreement with the positive correlation of PDR with MAP found in our study. Niboyet et al (2011) did not, however, detect sensitivity of PDR to warming of 1 • C for 8 years. The MAT gradient in our study spans 1.9 • C (Table 1) and the negative correlation of MAT with PDR represent long-term climatic conditions rather than short-term increases that have been experimentally induced.…”

Effects of multiple global change treatments on soil N2O fluxes

“…However a fire burned two replicate blocks in July of 2003 (Henry et al 2006;Gutknecht et al 2010). The impact of the fire treatment on soil N 2 O emission rates and related processes is discussed elsewhere (Niboyet et al 2011a), and is not included in this analysis.…”

“…Nitrogen addition stimulates both nitrification and denitrification (Barnard et al 2005), enhancing N 2 O emissions from soils in both natural and managed ecosystems (Bouwman et al 2002;Stehfest and Bouwman 2006;van Groenigen et al 2010). Elevated CO 2 has been shown to increase and decrease nitrification and denitrification enzyme activities (Barnard et al 2005;Niboyet et al 2010Niboyet et al , 2011a, decrease and increase available N (Reich et al 2006), increase C input to soil (de Graaff et al 2006), and increase soil water content (Arnone and Bohlen 1998), all of which can affect N 2 O efflux. Although there is considerable variation, on average, elevated CO 2 increases N 2 O efflux from soils (van Groenigen et al 2011).…”

The soil-plant relationship of nitrogen use in three tropical tree species

“…The greater availability of this ion during the wet season is influenced by precipitation and humidity (Table 2). Changes in precipitation regimes, through changes in soil moisture, significantly altered the nitrogen availability processes in the soil (Dijkstra et al, 2010 andNiboyet et al, 2011). Furthermore, this variation is also influenced by the prevailing soil in the area described by Genú et al (2010) as typical dystrophic Red-Yellow Argisol -PVAd (Tables 1 and 2).…”