Details

Autor(en) / Beteiligte

• Soper, Fiona M.
• Boutton, Thomas W.
• Groffman, Peter M.
• Sparks, Jed P.

Titel

Nitrogen trace gas fluxes from a semiarid subtropical savanna under woody legume encroachment

Ist Teil von

• Global biogeochemical cycles, 2016-05, Vol.30 (5), p.614-628

Ort / Verlag

Washington: Blackwell Publishing Ltd

Erscheinungsjahr

2016

Link zum Volltext

Quelle

Elektronische Zeitschriftenbibliothek - Frei zugängliche E-Journals

Beschreibungen/Notizen

• Savanna ecosystems are a major source of nitrogen (N) trace gases that influence air quality and climate. These systems are experiencing widespread encroachment by woody plants, frequently associated with large increases in soil N, with no consensus on implications for trace gas emissions. We investigated the impact of encroachment by N‐fixing tree Prosopis glandulosa on total reactive N gas flux (Nt = NO + N2O + NOy + NH3) from south Texas savanna soils over 2 years. Contrary to expectations, upland Prosopis groves did not have greater Nt fluxes than adjacent unencroached grasslands. However, abiotic conditions (temperature, rainfall, and topography) were strong drivers. Emissions from moist, low‐lying Prosopis playas were up to 3 times higher than from Prosopis uplands. Though NO dominated emissions, NH3 and NOy (non‐NO oxidized N) comprised 12–16% of the total summer N flux (up to 7.9 µg N m−2 h−1). Flux responses to soil wetting were temperature dependent for NO, NH3, and NOy: a 15 mm rainfall event increased flux 3‐fold to 22‐fold after 24 h in summer but had no effect in winter. Repeated soil wetting reduced N flux responses, indicating substrate depletion as a likely control. Rapid (<1 min) increases in NO emissions following wetting of dry soils suggested that abiotic chemodenitrification contributes to pulse emissions. We conclude that temperature and wetting dynamics, rather than encroachment, are primary drivers of N flux from these upland savannas, with implications for future emission patterns under altered precipitation regimes. Key Points Woody legume (Prosopis) encroachment does not increase N trace gas emissions from upland savannas Less commonly measured compounds (NH3 and NOy) contribute 12‐16% of summer N flux Emissions controlled by topography, temperature, and wetting, including rainfall frequency