© 1990 Heron Publishing—Victoria, Canada
Low humidity can cause uneven photosynthesis in olive (Olea europea L.) leaves
Francesco Loreto (1) and Thomas D. Sharkey (1, 2)
1. Department of Botany, University of Wisconsin, 430 Lincoln Drive, Madison, WI 53706, USA / 2. Author to whom correspondence should be addressed / Received December 21, 1989
Summary
We examined the photosynthetic responses of olive (Olea europea L.) leaves exposed to either (a) two hours of high leaf-to-air vapor pressure difference (vpd) or (b) four 30-min cycles
of high vpd separated by 15-min periods of recovery at low vpd. Neither treatment affected photosynthesis when vpd was less
than 3.0 kPa. Photosynthesis by mature leaves was also insensitive to higher vpd, but photosynthesis of young leaves was reduced
by both treatments at a vpd higher than 3.2 kPa. This effect of vpd was much smaller under high intercellular CO2 pressure. Autoradiograms showed that under a vpd of 3.2 kPa, mature leaves photosynthesized uniformly, but patches of reduced
CO2 fixation occurred in the distal part of young leaves. We conclude that heterogeneities in photosynthesis along the length
of the leaf caused the apparent reduction of photosynthesis in our experiments. This pattern of patchy photosynthesis was
different from that observed in mesophytic herbs, but the effect on gas exchange analysis was the same. In this case, apparent
biochemical effects of low humidity on photosynthesis of young olive leaves are likely an artifact.
