Concentration gradients of ozone and other trace gases in and above cereal canopies

• The concentration of ozone (O-3) above and within a barley canopy and a wheat canopy was studied. Compared to the concentration at 1.1 m above the ground (0.1 m above the 1 m tall canopy), the concentration within the canopy (0.3 m above ground) was typically reduced by approximately 20 % during the day and 40 % during the night for both barley and wheat, reflecting the slower mixing of air in the lower wind speeds of the night. The variation in ozone reduction in the canopy during the hours with the highest average wind speeds (11:00-16:00) could partly be explained by the effect of vapour pressure deficit on stomatal conductance. The concentration gradients of nitrogen dioxide (NO2) above and into the canopy were weaker but similar to that of O-3 while the measurements suggested emission of nitric oxide (NO). During the day the carbon dioxide (CO2) concentration had a local minimum at the top of the canopy reflecting the photosynthesis activity of the sunlit, non-senescent part of the canopy, while during the night very high concentrations of CO2 were observed within and immediately above the canopy as a result of respiration in combination with limited air mixing. Inside open-top chambers no concentration gradients of O-3 into the canopy or horizontally above the canopy could be detected.

Subject headings

NATURVETENSKAP  -- Biologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences (hsv//eng)

Keyword

OPEN-TOP CHAMBERS; WHEAT; VEGETATION; FLUXES; DEPOSITION; PROFILES; EXPOSURE; QUALITY; SURFACE; FOREST

Publication and Content Type

ref (subject category)

art (subject category)