A 3‐year continuous record of nitrogen trace gas fluxes from untreated and limed soil of a N‐saturated spruce and beech forest ecosystem in Germany: 1. N₂O emissions

Abstract

Abstract. For 3 years we followed the complete annual cycles of N20 emission rates with 2-hour resolution in spruce and beech plantations of the H6glwald Forest, Bavaria, Germany, in order to gain detailed information about seasonal and interannual variations of N20 emissions. In addition, microbiological process studies were performed for identification of differences in N turnover rates in the soil of a spruce and a beech site and for estimation of the contribution of nitrification and denitrification to the actual N20 emission. Both pronounced seasonal and extreme interannual variations of N20 emissions were identified. During long-term frost periods, while the soil was frozen, and during soil thawing, extremely high N20 emissions occurred, contributing up to 73% to the total annual N20 loss. The enormous N20 releases during the long-term frost period were due to high microbial N turnover rates (tight coupling of ammonification, nitrification, denitrification) in small unfrozen water films of the frozen soil at high concentrations of easily degradable substrates derived from the enormous pool of dead microbial biomass produced during the long-term frost period. Liming of a spruce site resulted in a significant increase in ammonification, nitrification, and N20 emissions as compared with an untreated spruce control site. The beech control site exhibited 4-5 times higher N20 emissions than the spruce control site, indicating that forest type itself is an important modulator of N20 release from soil. At all sites, nitrification contributed ---70% to the N20 flux, whereas denitrification contributed markedly less (---30%). There was a significant positive correlation between amount of in situ N input by wet deposition and magnitude of in situ N20 emissions. At the beech site, 10% of the actual N input was released from the soil in form of N20, whereas at the spruce site the fraction was 0.5%. N20 emission rates were positively correlated with net nitrification rates. The results demonstrate the need for long-term measurements over several years for more precise estimates of annual N20 losses from forest ecosystems. On the basis of our results we conclude that the importance of temperate and boreal forests for the global N20 source strength may have been significantly underestimated in the past and that these forests contribute most likely >> 1.0 Tg N20 N.

Meeting Cereal Demand While Protecting Natural Resources and Improving Environmental Quality

“…However, most of these estimates were obtained from small experimental field plots, which may not be representative of production-scale fields. Therefore, most currently used simulation models fail to account for large pulses of N 2 O emissions caused by spring thawing (130), rapid soil warming (131), tillage and irrigation events (132), and N application (120), which may greatly affect annual emission rates and the net global warming potential of an agroecosystem (133). And although C sequestration is often increased in systems that receive N fertilizer, the energy costs of N fertilizer and associated CO 2 emissions must also be included in the net greenhouse forcing budget (134).…”

Sources of nitrous oxide emitted from European forest soils

“…Several independent studies have demonstrated that N 2 O is emitted in significant quantities from forest ecosystems (e.g. Ambus and Christensen, 1995;Bowden et al, 1990;Schmidt et al, 1989;Struwe and Kjøller, 1994;Papen and Butterbach-Bahl, 1999). In Europe, forest ecosystems cover about 1.9 Mill.…”

Emissions of nitrous oxide from three tropical forests in Southern China in response to simulated nitrogen deposition

“…Although abiological processes (e.g., chemodenitrification) may account for a small portion of total soil derived N 2 O, the biological processes of nitrification NH are believed to be the predominant sources of N 2 O production in soils (Williams et al 1992;Wrage et al 2001). Forest soils have been acknowledged to represent significant sources of N 2 O emission (Papen and Butterbach-Bahl 1999;Butterbach-Bahl et al 2002;Skiba et al 2004). The dominant source for N 2 O from tropical forest soils was estimated to be in the range of 2.2-3.7 Tg N year −1 (24% of the total source strength) to the global atmospheric N 2 O budget (Prather and Ehhalt 2001).…”

“…Soil biological N 2 O production is controlled by a set of physical, chemical and biological factors. Soil moisture content, soil temperature and nutrient availability are regarded as key in regulating soil N 2 O production in forests (Papen and Butterbach-Bahl 1999;Brumme et al 1999;Smith et al 2003). An increase in these factors usually enhances N 2 O emission from forest soil.…”