Denitrification and nitrous oxide emissions from riparian forests soils exposed to prolonged nitrogen runoff

Abstract

Compared to upland forests, riparian forest soils have greater potential to remove nitrate (NO 3 ) from agricultural runoff through denitrification. It is unclear, however, whether prolonged exposure of riparian soils to nitrogen (N) loading will affect the rate of denitrification and its end products. This research assesses the rate of denitrification and nitrous oxide (N 2 O) emissions from riparian forest soils exposed to prolonged nutrient runoff from plant nurseries and compares these to similar forest soils not exposed to nutrient runoff. Nursery runoff also contains high levels of phosphate (PO 4 ). Since there are conflicting reports on the impact of PO 4 on the activity of denitrifying microbes, the impact of PO 4 on such activity was also investigated. Bulk and intact soil cores were collected from N-exposed and non-exposed forests to determine denitrification and N 2 O emission rates, whereas denitrification potential was determined using soil slurries. Compared to the non-amended treatment, denitrification rate increased 2.7-and 3.4-fold when soil cores collected from both N-exposed and non-exposed sites were amended with 30 and 60 lg NO 3 -N g -1 soil, respectively. Net N 2 O emissions were 1.5 and 1.7 times higher from the N-exposed sites compared to the non-exposed sites at 30 and 60 lg NO 3 -N g -1 soil amendment rates, respectively. Similarly, denitrification potential increased 17 times in response to addition of 15 lg NO 3 -N g -1 in soil slurries. The addition of PO 4 (5 lg PO 4 -P g -1 ) to soil slurries and intact cores did not affect denitrification rates. These observations suggest that prolonged N loading did not affect the denitrification potential of the riparian forest soils; however, it did result in higher N 2 O emissions compared to emission rates from non-exposed forest soils.

Nitrous oxide fluxes from the littoral zone of a lake on the Qinghai-Tibetan Plateau

“…Hot spots are recently identified as of major importance in quantifying process rates and gas fluxes in many ecosystems (McClain et al 2003). Therefore, based on numerous studies all over the world, the interface zone of aquatic and terrestrial ecosystems, such as littoral zones or riparian zones, has been regarded as hotspots of N 2 O fluxes (Groffman et al 2000;Hefting et al 2003;Huttunen et al 2003b;Dhondt et al 2004;Hernandez and Mitsch 2006;Ullah and Zinati 2006;Wang et al 2006). However, with the limited data of N 2 O flux in this study, we could not make an accurate estimation of total N 2 O effluxes from littoral zones of lakes on Qinghai-Tibetan Plateau.…”

“…Gradually recognized as critical "hot spots" of N transformation in the landscape in recent years (Groffman et al 2000;Wang et al 2006), riparian zones of rivers and littoral zones of lakes have been regarded as the important sources of N 2 O emissions by some researchers (Bernal et al 2003;Hefting et al 2003;Dhondt et al 2004;Hernandez and Mitsch 2006;Ullah and Zinati 2006;Hunt et al 2007). Most of such studies focused on littoral zones in the agriculture landscape with high N loading, while little is known about N 2 O emissions littoral zones in the grazing landscape, which is also under a high N transformation rate due to livestock grazing (Gao et al 2008).…”

Flooding-related increases in CO<sub>2</sub> and N<sub>2</sub>O emissions from a temperate coastal grassland ecosystem

“…Several other environmental factors such as pH, oxygen concentration and nitrogen availability are known to affect the production of N 2 O (Ullah and Zinati, 2006;Van den Heuvel et al, 2011;Burgin and Groffman, 2012). In this study, the lower pH, as well as a higher nitrogen availability and higher MBC at the LFS, would be expected to favour N 2 O emissions (Liu and its progressive decrease through the aerobic period (periods C and E) in both sites (Table 2) indicate increased nitrification and ammonia oxidation that may lead to N 2 O production as aeration of soil and gas diffusion improves (Firestone and Davidson, 1989).…”

Removal of nitrate-N by antibiotic exposed bacterial isolates from constructed wetlands

“…Ideal C/N ratio for denitrification depends on denitrifying bacterial strain and the environment. Ullah and Zinati (2006) reported the dependency of the relative nitrous oxide production on C/N ratio for different nitrate input levels. Several other studies have recorded a decline in nitrous oxide production with a decrease of the C/N ratio in leaf litter (Erickson et al 2001;Wick et al 2005).…”