Tim Clough

Soil and Physical Sciences, Faculty of Agriculture and Life Sciences, Lincoln University, New Zealand

The focus of Tim’s research is nitrogen cycling in grazed pastures as it relates to the understanding and mitigation of reactive nitrogen fluxes, especially nitrous oxide. Tim’s research makes strong use of stable isotope tools to elucidate the fate, sources and transformations of nitrogen and carbon in soils.
Tim has served several terms as an associate editor for both the Journal of Environmental Quality and Soil Science Society of America Journal, and as a Technical Editor for the Journal of Environmental Quality. Currently he is the Senior Editor for the New Zealand Journal of Agricultural Research and a Chief Editor for Soil Biology & Biochemistry, and was recently made a Fellow of the Soil Science Society of America.

Keynote: Denitrification: what do we know and where to from here?

An overview of N cycling in agricultural systems will be presented as it relates to denitrification. Using the ruminant urine patch in a grazed agricultural system, as a model to cover the dynamics and pools that occur in agricultural N cycling, the interactive effects of soil chemistry, microbiology and soil physics will be covered. Commencing with the urea substrate, the N substrates that are subsequently form and feed into the denitrification processes will be identified and discussed with respect to their contributions to denitrification. Where applicable, concurrent processes that compete for these substrates and which may offset denitrification will be described. Overlying this presentation will be linked examples and studies that demonstrate both the dynamic microbial nature of agricultural systems and the soil physical conditions that switch denitrification on and off. Finally, drawing on our current understanding and the previous DASIM presentations, gaps in our knowledge and future directions for tracing denitrification and mitigating N losses will be discussed.

Lars Reier Bakken

Norwegian University of Life Sciences

LB used to be a “jack of all trades” in soil biology, but since 2004 his research has narrowed down to nitrogen transformations in general, and anoxic respiration in particular. LB formed the NMBU Nitrogen Group together with Åsa Frostegård and Peter Dörsch. The research of NMBUNG spans from field experiments and process studies to pure culture investigations of the physiology and regulatory biology of nitrifying and denitrifying prokaryotes. Link to personal webpage.

Keynote: Denitrification – ecophysiology ruminations

The current escalation of the nitrogen cycle (fertilization and combustion) cause accumulation of N2O in the atmosphere, primarily through denitrification. To mitigate N2O emissions, we must improve our understanding of the mechanisms that control the N2O emissions at different scales: enzyme-, cellular-, community- and systems-level. Thus, progress in combatting N2O emission from denitrification demands trans-disciplinary communication and collaboration, which is the explicit aim of this very timely conference. The point of departure for my introductory talk will be the “physiology of denitrification”, as studied at the enzyme and cellular level. I will summarize some recent progress in understanding the regulatory networks of the denitrification genes, and the role of denitrification in sustaining respiratory metabolism, both in heterotrophic and autotrophic prokaryotes.

I will speculate about the reasons for the ubiquity of truncated denitrifiers, i.e. organisms that conduct only one or two steps the entire pathway from nitrite to N2, and extend this to a speculative discussion about the selective advantage of reducing N2O to N2, hopefully inspiring someone to invent new integrative approaches to shed light on this crucial question.

Finally, I will discuss the prospects for progress through studies of the biochemistry and regulatory biology of model organism versus process studies in complex systems. The study of model organisms provides essential “scaffolds” for understanding complex systems, and useful hypotheses that can be tested in whole-system experiments. And vice versa: explorative whole-system investigations, harnessed with advanced isotope methods to trace specific transformations, may unravel novel phenomena, that should be tested and understood by investigating model organisms.