NOS-A - Mechanisms and atmospheric importance of nitrous oxide uptake in soils

Principal investigator: Prof. Pertti Martikainen/Assoc. Prof. Marja Maljanen

Funding period: 2012-2016 (Academy of Finland)

Nitrous oxide contributes 6% to the total increase in the radiative forcing of the atmosphere. The anthropogenic N2O emissions mainly result from agricultural land-use which stimulate microbial N2O production in soil. Recent studies, however, suggest that N2O has also a missing sink in soils, but data on this are yet rare. The purpose of this project is thus to explicitly address the mechanisms and atmospheric importance of N2O uptake in soils. The principle scientific questions are: when and why N2O uptake takes place in aerobic soils and what is the magnitude of the uptake rate? We propose to answer these research questions through two main research objectives: 1) to identify the environmental/microbial conditions supporting uptake of N2O in aerobic soils, and 2) to show the atmospheric importance of N2O uptake in aerobic soils. The objectives are met by a multidisciplinary investigation across several scales (from molecules to ecosystem) on aerobic agricultural and natural soils (forest, tundra) with different soil characteristics and a water-logged natural mire ecosystem as a reference site.

With a combination of N2O flux measurements, soil N2O profiles, detailed soil/environmental assays and modern stable isotope approaches, we will be able to track the fate of N2O in soils and get valuable know-how on factors regulation N2O uptake. More detailed understanding on mechanisms underlying N2O uptake will be gained by complementary laboratory incubations aiming at determining effects of hydrology, oxygen content, nutrient status and availability of organic carbon on N2O reduction. All experiments will be thoroughly inter-linked with molecular assays (qPCR, PCR-TGGE) to identify genes involved in denitrification, e.g. nirS, nirK and nosZ, and linkages that mediate N2O uptake in the soil. To quantitatively address the fluxes/uptake rates and thus the N2O sink potential of aerobic soils highly sensitive chamber methods including - at one site - an advanced eddy covariance technique with N2O laser, will be applied. The atmospheric effect of N2O and CH4 fluxes will be compared by the GWP approach. This proposal integrates a whole array of new, cutting-edge technologies that have rarely if ever been applied together in research on N2O dynamics (e.g., isotopes, metatranscriptomics and eddy covariance).