Production Practices and Quality Assessment of Food Crops. Vol. 1

198 S. del Valle-Tascon and J. L. Carrasco-Rodriguez
suggested, exposure-response curves derived under chamber conditions can not be
used directly to estimate quantitative effect under chamberless (ambient) conditions.
More experimental work must be done in order to give an answer to this question.
13. CROP YIELD LOSS
There is a considerable volume of published data on the effect of polluted air on
a wide range of agricultural yield reduction (Adams et al., 1988; Heagle, 1989;
US EPA, 1996). The International Cooperative Program on Effects of Air Pollutants
on Natural Vegetation and Crops (Kärenlampi and Skärby, 1996) and the USA
National Crops Loss Network (US EPA, 1986; Adams et al., 1988; Heagle, 1989;
US EPA, 1996) are the principal programs dedicated to studying the impacts of
O 3 on crops. These and other reports have demonstrated that air polluted O 3 showed
a significant decrease in yield losses; these losses being influenced by crop species
and cultivars, moisture stress and other growth conditions. To sum up, yield losses
ranged from near 0 up to 39%. Complete reduction of yield has been observed during
O 3 episodes (Velissariou, 1999).
14. INDICATORS OF OZONE STRESS
Initial studies on the effect of O 3 on crop species were centred on the reduction
of agronomical yield. Later on, in order to understand the action mechanism of
O 3 this interest area of agronomical yield has been displaced by other injury effects
such us physiological responses. The physiological changes observed in the presence
of O 3 polluted air are reduced net photosynthesis, increased respiration rate,
membrane lipid peroxidation, enhanced rate of senescence, reduced transpiration,
and inhibition of translocation to roots (Cooley and Manning, 1987; Darrall, 1989;
Heath, 1994b; Dizengemel and Pertins, 1994; Mudd, 1996; Taylor and Ferris,
1996; Sandermannn, 1996; Langebartels et al., 1997; Heath and Taylor, 1997; Pell
et al., 1997; Schraudner et al., 1997). The most important of these techniques are
spectral reflectance, fluorescence and videography.
Imaging techniques (reflectance and near infrared imaging) are used for earlier
detection of plant stress induced by tropospheric O 3 (Chaerle and van der Straeten,
2000). Stress induced physiological damage in plants is manifested in altered
reflectance spectrum. Several spectral indices have been proposed as stress indicators
(Hunt et al., 1987). Leaf spectral reflectance as a rapid method for detecting
O 3 stress has been used for crop species (Runeckles and Resh, 1975; Schutt et al.,
1984; Carter et al., 1992; Williams and Ashenden, 1992). A decreased infrared
reflectance is detectable for clover leaves after O 3 treatment, although no visible
foliar damage symptoms could be observed (Kraft et al., 1996). Ozone-treated leaves
showed lower water content, photosynthetic pigments, and PSII activity (Rudorff
et al., 1996).
Measurement of chlorophyll a fluorescence is a technique for measuring
incipient O 3 effect in the field (Schreiber et al., 1998 and references therein). This