Nitrogen trace gas fluxes from a semiarid subtropical savanna under woody legume encroachment
Nitrogen trace gas fluxes from a semiarid subtropical savanna under woody legume encroachment
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DOI：
10.1002/2015gb005298
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发表时间：
2016-05-01
影响因子：
5.2
通讯作者：
Sparks, Jed P.
中科院分区：
文献类型：
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作者：
Soper, Fiona M.;Boutton, Thomas W.;Sparks, Jed P.
稀树草原生态系统是影响空气质量和气候的氮(N)痕量气体的主要来源。这些系统正经历着木本植物的广泛侵蚀，往往与土壤氮的大幅增加有关，对微量气体排放的影响没有达成共识。研究了2年来固氮树Prosopis glandulosa对南德州稀树草原土壤中N-t=NO+N2O+NOY+NH3总反应氮通量的影响。与预期相反，旱地Prosopis树林并没有比邻近的未受侵蚀的草原有更大的N-t通量。然而，非生物条件(温度、降雨和地形)是强劲的驱动因素。来自潮湿、低洼的Prosopis playas的排放量比Prosopis高地高出3倍。虽然NO排放占主导地位，但NH3和NOY(非NO氧化N)占夏季总N通量(高达7.9U GNM(-2)h(-1))的12-16%。土壤湿润对NO、NH3和NOY的通量响应与温度有关：夏季一次15 mm的降雨使通量在24小时后增加3倍至22倍，但在冬季没有影响。反复的土壤湿润降低了氮素通量响应，表明基质耗竭可能是一种控制措施。快速(
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 (N-t=NO+N2O+NOy+NH3) from south Texas savanna soils over 2 years. Contrary to expectations, upland Prosopis groves did not have greater N-t 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 mu gNm(-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 (