N2O emission from a tomato rockwool culture is highly responsive to photoirradiation conditions

- N2O emissions observed continuously from rockwool-based tomato cultures.
- N2O emissions related to photoirradiation intensity and time of nitrogen fertilization.
- N2O emissions correlated negatively with photoirradiation

Previously, we found that rhizospheric N2O emissions from a tomato rockwool culture respond quickly and directly to nitrogen fertilization. Interestingly, the amount of emissions increased considerably when fertilization was shifted from day-time to night-time. If this phenomenon is revealed in response to photoirradiation, the N2O emissions would be hypothesized as a matter of not only a bacterial activity, but also an ecophysiological status of tomato plants. Therefore, we observe the effects of detailed photoirradiation conditions on N2O emissions to confirm the hypothesis. Tomato was grown by a rockwool culture with constant intermittent fertilization. The N2O emissions were observed continuously using an automatic monitor to relate them to photoirradiation intensity during the day-time fertilization and to detect any effect of supplemental lighting on N2O emissions during the night-time fertilization. The daily total N2O emissions was negatively correlated with daily total solar radiation (r = −0.83). It was obvious that more than 15 J m−2 s−1 of photon flux density (PFD) were almost evenly effective in suppressing emissions. Supplemental lighting during night-time fertilization confirmed the negative effects of photoirradiation on N2O emissions, which were revealed as a significant PFD/irradiation style dependency and a wavelength dependency. Notably, the supplemental lighting advanced the reduction of water content and electric conductivity in the rockwool. The clear negative correlation between N2O emissions and photoirradiation could be the result of the acceleration of water and/or nutrient uptake via tomato roots and a counter-result of the deceleration of bacterial N consumption by photoirradiation.