Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
4442551 | Atmospheric Environment | 2008 | 10 Pages |
Abstract
The vapour pressure deficit (VPD) in open-top chambers (OTCs) was analysed in relation to time of day and ambient meteorology. Effects of observed VPD differences (ÎVPD) between OTCs and the ambient air (AA) on stomatal conductance (gs) were simulated using 10 model functions from the literature. The dataset originated from 17 OTC crop experiments performed in Belgium, Germany and Sweden. ÎVPD is the resulting difference between the OTC effect on es(T), which is the temperature-dependent saturation pressure of water vapour and the OTC effect on ea, which is the prevailing partial pressure of water vapour in the air (ÎVPD = Îes(T) â Îea). Both Îes(T) and Îea were positive during daylight hours. ÎVPD was small in comparison and sensitive to changes in Îes(T) or Îea. ÎVPD was negative between 07:30 and 10:30 and positive thereafter with a maximum at 20:30 (local time). The positive afternoon ÎVPD was due to an early decrease in Îea, probably caused by ceased transpiration, while the positive Îes(T) persisted throughout the evening, most likely because of restrained cooling in the OTCs. Both the negative morning ÎVPD and the positive evening ÎVPD were more pronounced during clear, warm and dry weather. Circumstances when VPD had a stronger limiting effect on gs inside the OTCs compared to in the ambient air coincided with high ambient ozone concentrations ([O3]). Calculated wheat O3 uptake over an [O3] threshold of 40 nmol molâ1 was reduced by 8.7% in OTCs, assuming that VPD was the only factor limiting gs and that gs was the only resistance for O3 uptake. VPD is one factor of considerable importance for gs and the OTC impact on VPD may contribute to an underestimation of O3 effects expressed in relation to the external O3 exposure.
Related Topics
Physical Sciences and Engineering
Earth and Planetary Sciences
Atmospheric Science
Authors
K. Piikki, L. De Temmerman, P. Högy, H. Pleijel,