Plant and Soil, Jan, 2012, Vol.350(1-2), p.297(14)
Byline: Benjamin Wolf (1), Ralf Kiese (1), Weiwei Chen (2), Rudiger Grote (1), Xunhua Zheng (2), Klaus Butterbach-Bahl (1) Keywords: Freeze-thaw; Impedance concept; [N.sub.2]O; Steppe; Biogeochemical modelling; Grazing intensity Abstract: Aims Temperate grassland is one of the major global biome types and is widely used as rangeland. Typically, cold winters are followed by a transition period with soil thawing that may last from days to weeks. Pulse [N.sub.2]O emissions during freeze-thaw events have been observed in a range of temperate ecosystem types and may contribute significantly to annual [N.sub.2]O emissions. It was shown recently that spring thaw pulse [N.sub.2]O emissions dominated annual [N.sub.2]O emissions in a steppe region of Inner Mongolia. Even though biogeochemical models are increasingly used for up scaling of [N.sub.2]O emissions from terrestrial ecosystems, they still need to be further developed to be capable of both simulating pulse [N.sub.2]O emission during spring thaw and accounting for the impact of grazing on soil [N.sub.2]O emissions in general. Methods In this study, we modified an existing biogeochemical model, Mobile-DNDC, to allow an improved simulation of plant production, snow height, and soil moisture for steppe in Inner Mongolia exposed to different grazing intensities. The newly introduced routines relate maximum snow height to end-of-season biomass (ESSB), to account for decreased plant productivity due to grazing and consider the increase of resistance (impedance) of soil ice on the soil hydraulic conductivity. Results The implementation of the impedance concept, which means the consideration of decreased hydraulic conductivity in frozen soil, resulted in an improved simulation of soil water content and decreased simulated oxygen content in the top soil during freeze-thaw periods. Increased soil moisture and associated oxygen limitation stimulated [N.sub.2]O emission by enhanced denitrification. Based on observations in the field, maximum snow height was limited by ESSB, protecting snow against erosion by wind. Since grazing reduced biomass and thereby snow cover, water availability during spring thaw was smaller at grazed sites as compared to ungrazed sites. In agreement with field observations, lower water content and anaerobiosis resulted in decreased [N.sub.2]O emissions during spring thaw. Conclusions The introduction of the impedance concept into Mobile-DNDC is a major step forward in simulating pulse [N.sub.2]O emissions from soils during spring-thaw. Author Affiliation: (1) Institute for Meteorology and Climate Research (IMK-IFU), Karlsruher Institute of Technology, Kreuzeckbahnstrasse 19, 82467, Garmisch-Partenkirchen, Germany (2) State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute for Atmospheric Physics, Chinese Academy of Sciences (IAP-CAS), 100029, Beijing, China Article History: Registration Date: 07/07/2011 Received Date: 23/02/2011 Accepted Date: 07/07/2011 Online Date: 23/07/2011 Article note: Responsible Editor: Hans Lambers.
Biomes -- Analysis ; Biomes -- Models ; Biomes -- Environmental Aspects ; Soil Moisture -- Analysis ; Soil Moisture -- Models ; Soil Moisture -- Environmental Aspects ; Atmospheric Physics -- Analysis ; Atmospheric Physics -- Models ; Atmospheric Physics -- Environmental Aspects ; Planetary Boundary Layer -- Analysis ; Planetary Boundary Layer -- Models ; Planetary Boundary Layer -- Environmental Aspects ; Steppes -- Analysis ; Steppes -- Models ; Steppes -- Environmental Aspects ; Air Pollution Control -- Environmental Aspects ; Air Pollution Control -- Analysis ; Air Pollution Control -- Models ; Denitrification -- Analysis ; Denitrification -- Models ; Denitrification -- Environmental Aspects ; Terrestrial Ecosystems -- Analysis ; Terrestrial Ecosystems -- Models ; Terrestrial Ecosystems -- Environmental Aspects ; Hydrogeology -- Analysis ; Hydrogeology -- Models ; Hydrogeology -- Environmental Aspects ; Atmospheric Chemistry -- Analysis ; Atmospheric Chemistry -- Models ; Atmospheric Chemistry -- Environmental Aspects
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