Eclipse Effects on CO₂ Profile within and above Sorghum Canopy

Abstract

We analyzed the effects of a partial solar eclipse (22 July 2009) on microclimate including vertical gradients of CO₂ concentrations ([CO₂]), so called [CO₂] profile, in a mature sorghum canopy. Together with CO₂ measurement, major photosynthetic drivers of microclimate, light intensity, temperature and atmospheric H₂O concentration ([H₂O]) were also measured simultaneously at the same place and height. [CO₂] at 6.0, 3.2, 2.1, 1.4, 0.7, 0 m above the ground (canopy height was 3.2 m) increased by 5.8, 4.8, 9.0, 7.8, 6.4, 7.6 μmol mol^-1, respectively, from 1 hour before the eclipse maximum to the eclipse maximum, during which the incident solar radiation above the canopy dropped by 1473 μmol photons m^-2 s^-1. However, it declined by 3.4, 10.6, 10.8, 6.0, 5.4, and 5.8 μmol mol^-1, respectively, from the eclipse to 1 hour later, during which the incident radiation increased by 1350 μmol photons m^-2 s^-1. The [CO₂] profile during the eclipse was uniform except for higher [CO₂] near the ground. Comparative analysis of the effect of light intensity on the microclimate during the eclipse-induced light decreasing phase (ELDP) and eclipse-induced light increasing phase (ELIP) revealed that [CO₂], [H₂O], temperature and relative humidity (RH) are significantly correlated with the light intensity above the canopy in a nearly linear fashion. Furthermore it indicated that detected less light-reacted canopy photosynthesis at a higher layer within the canopy during ELIP might be due to slower response of stomatal opening (than closing) to the light intensity above the canopy.