N 2 O emissions from plants are reduced under photosynthetic activity.

New plant functions in the exchange of greenhouse gases between ecosystems and atmosphere have recently been discovered. We tested whether photosynthetic activity has an effect on N 2 O emission rates from incubated plant-soil systems.Two laboratory experiments were performed. One to unravel possible effect of photosynthetic activity on the net N 2 O ecosystem exchange for two species (beech and ash saplings). The other to account for possible effects from rhizosphere and aboveground plant parts separately (ash sapling only).Total N 2 O emissions from both plant and plant-soil systems were significantly lower under light than in darkness (31%-65%). The photosynthetic effect only applied to the aboveground plant parts.Underlying processes have now to be unraveled to improve our understanding of ecosystem functioning. This will improve modeling and budgeting of greenhouse gas exchanges between ecosystems and the atmosphere.