Multi-year measurements of stomatal and non-stomatal fluxes

• Measurements of ozone, sensible heat, and latent heat fluxes, as well as relative humidity, temperature, pressure, wind speed, leaf area index, ambient ozone, and plant physiological parameters were made at a northern mixed hardwood forest located at the University of Michigan Biological Station (UMBS) in northern Michigan during the growing seasons 2002 through 2005. The ozone measurements were used to calculate total ozone flux and partitioning between stomatal and non-stomatal sinks. Total ozone flux varied diurnally with downward flux reaching -100 μmol m-2 h-1 at midday, at or near zero at night. Mean daytime canopy conductance varied over the four years: 0.39 mol m-2 s-1 (2002), 0.41 mol m-2 s-1 (2003), 0.52 mol m-2 s-1 (2004), and 0.43 mol m-2 s-1 (2005). Stomatal conductance showed expected patterns of behavior with respect to photosynthetic photon flux density (PPFD) and vapor pressure deficit (VPD). Estimated peak growing season stomatal ozone burden (flux) was 2.9 x105 nmol m-2 in 2002, 5.6 x105 nmol m-2 in 2003, 6.6 x105 nmol m-2 in 2004, and 4.1 x105 nmol m-2 in 2005. Non-stomatal conductance for ozone increased monotonically with increasing PPFD, and increased with temperature before falling off again at high temperature. Daytime non-stomatal ozone sinks were large and varied with time and environmental drivers. Daytime non-stomatal ozone conductance accounted for as much as 61% (2002), 31% (2003), 36% (2004), or 57% (2005) of canopy conductance, with the non-stomatal partition representing 4.2x105 nmol m-2 (2002), 2.0x105 nmol m-2 (2003), 3.5x105 nmol m-2 (2004), 3.5x105 nmol m-2 (2005) of the flux. Non-stomatal ozone conductance was strongly diurnal and a significant proportion of total canopy conductance.

Subject headings

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Meteorologi och atmosfärforskning (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Meteorology and Atmospheric Sciences (hsv//eng)

Publication and Content Type

vet (subject category)

kon (subject category)