Delayed NH3 and N2 O uptake by maize leaves

Quantifying nitrous oxide fluxes on multiple spatial scales in the Upper Midwest, USA

This study seeks to quantify the roles of soybean and corn plants and the cropland ecosystem in the regional N2O budget of the Upper Midwest, USA. The N2O flux was measured at three scales (plant, the soil-plant ecosystem, and region) using newly designed steady-state flow-through plant chambers, a flux-gradient micrometeorological tower, and continuous tall-tower observatories. Results indicate that the following. (1) N2O fluxes from unfertilized soybean (0.03 ± 0.05 nmol m(-2) s(-1)) and fertilized corn plants (-0.01 ± 0.04 nmol m(-2) s(-1)) were about one magnitude lower than N2O emissions from the soil-plant ecosystem (0.26 nmol m(-2) s(-1) for soybean and 0.95 nmol m(-2) s(-1) for corn), confirming that cropland N2O emissions were mainly from the soil. (2) Fertilization increased the corn plant flux for a short period (about 20 days), and late-season fertilization dramatically increased the soybean plant emissions. (3) The direct N2O emission from cropland accounted for less than 20 % of the regional flux, suggesting a significant influence by other sources and indirect emissions, in the regional N2O budget.

Photosynthesis of Quercus suber is affected by atmospheric NH3 generated by multifunctional agrosystems

Montados are evergreen oak woodlands dominated by Quercus species, which are considered to be key to biodiversity conservation and ecosystem services. This ecosystem is often used for cattle breeding in most regions of the Iberian Peninsula, which causes plants to receive extra nitrogen as ammonia (NH(3)) through the atmosphere. The effect of this atmospheric NH(3) (NH(3atm)) on ecosystems is still under discussion. This study aimed to evaluate the effects of an NH(3atm) concentration gradient downwind of a cattle barn in a Montado area. Leaves from the selected Quercus suber L. trees along the gradient showed a clear influence of the NH(3) on δ(13)C, as a consequence of a strong limitation on the photosynthetic machinery by a reduction of both stomatal and mesophyll conductance. A detailed study of the impact of NH(3atm) on the photosynthetic performance of Q. suber trees is presented, and new mechanisms by which NH(3) affects photosynthesis at the leaf level are suggested.

Gaseous ammonia counteracts the response of Scots pine needles to elevated atmospheric carbon dioxide

Four-year-old saplings of Scots pine (Pinus sylvestris L.) were exposed for 8 wk in controlled-environment chambers to charcoal-filtered air (FA), FA supplemented with 754 mg m^-3 (650 μl 1^-1 )CO₂ , FA supplemented with l00 μ m¹³ NH₃ and FA+CO₂ +NH₃ . Elevated CO₂ induced a significant increase in the concentrations of NH₄ ⁺ and NO₃ in the soil solution, while exposure to NH₃ enhanced the soil NH₄ ^- concentration. Elevated CO₂ significantly increased needle biomass and area, and decreased specific leaf are (SLA) and N concentration in the needle. The activity of peroidase (POD) was decreased, while the activities of glutamine synthetase (GS) and glutamate dehydrogenase (GDH) were only slightly affected. Gaseous NH₃ enhanced the concentration of N. soluble proteins and the GS activity in the needless, while it decreased the POD and GDH activities. The effects of elevated CO₂ + NH₃ on needle biomass production, N Metabolism and POD activity were smaller than the effects of single exposures to elevated CO₂ or NH³ . Suggesting that elevated CO₂ and NH₃ counteract each other and disturb needle physiology. The possible mechanisms underlying the negative interactions of elevated CO₂ and NH₃ and discussed. The expected stimulation of biomass production by elevated CO₂ my be reduced in the presence of atmospheric NH₃ .