Adverse effects of ambient ozone on watermelon yield and physiology at a rural site in Eastern Spain

Abstract

The study reported was conducted to establish the impacts of photochemical oxidants (primarily ambient ozone, O $ ) on the yield of watermelon (Citrullus lanatus) at a site on the east coast of Spain. Fruit yield and quality were monitored in plots established in a commercial watermelon field exposed, in open-top chambers (OTCs), to nonfiltered air (NFA ; near-ambient levels of ozone) or charcoal-filtered air (decreased levels of photochemical oxidants including O $ ; CFA), or to ambient air (AA), during the 1988 and 1989 growing seasons. Ambient levels of O $ were found to exceed present UN-ECE (United Nations Economic Commission for Europe ; Convention on Long-Range Transboundary Air Pollution) critical level guidelines for the protection of crop yield by approx. twofold in 1988 and by approx. fivefold in 1989. Plants exposed to NFA and AA developed visible O $ injury on the upper surface of sun-exposed older leaves, and fruit yield (annual marketable fruit weight and number) was found to be depressed in OTCs ventilated with NFA in comparison with those receiving CFA. Consistent with inter-annual variations in O $ exposure, greater yield losses were experienced in 1989 (39%) than in 1988 (19%), an effect mediated predominantly by a decline in fruit number rather than average fruit weight. Exposure to ambient levels of ozone also slightly decreased fruit quality (4-8% decline in soluble solids content). Leaf gas exchange measurements made in the field in 1988 revealed effects of O $ on fruit yield and quality to be associated with a decline in the net CO # assimilation rate per unit leaf area under light saturation (A sat ) and stomatal conductance to water vapour (g s ), and enhanced rates of dark respiration. A\c i curves (where A is the net CO # assimilation rate per unit leaf area and c i is the mole fraction of CO # in the leaf intercellular air space) constructed for plants grown in laboratory-based closed chambers, and exposed to an accumulated O $ exposure similar to that experienced by plants in the field, suggested that the likely cause of the decline in photosynthetic capacity was (1) a decrease in the amount and\or activity of Rubisco and (2) an impaired capacity for regeneration of ribulose 1,5-bisphosphate, which was not mediated through changes in the photochemical efficiency of photosystem II (F v \F m , where F v is variable chlorophyll a fluorescence and F m is maximum chlorophyll a fluorescence). No shift in the relative stomatal limitation to photosynthesis was observed under the influence of O $ , suggesting that the decline in g s induced by the pollutant in both field and laboratory was the result, and not the cause, of the decrease in A sat . Ozone exposure also caused a decrease in C isotope discrimination (approx. 0.5=), a shift that revealed a departure from predicted theory based on supporting leaf gas exchange measurements. The study demonstrates that ambient levels of photochemical oxidants on the Spanish Mediterranean coast are high enough to adversely influence the yield a...

Growth response to ozone of annual species from Mediterranean pastures

“…The same day the plants were transplanted into pots they were introduced in slightly modified NCLAN-type OTCs (see Gimeno et al, 1999). Three 0 3 treatments were used: charcoal filtered air (CFA) presenting subphytotoxic 0 3 levels, non-filtered air (NFA) with close to ambient 0 3 levels and non-filtered air supplemented with 40 ppb 0 3 from 07:00 to 17:00 (GMT) 5 days week" 1 (NFA + ).…”

Tansley Review No. 115

“…Oshima et al (1979) reported that exposure to ozone decreased boll production in cotton, although boll size and the proportions of boll components were unaffected. Similarly, the adverse effect of ozone on floral initiation reported for muskmelon and watermelon by Fernandez-Bayon et al (1993) reduced fruit numbers and yield (Gimeno et al, 1999). Numerous studies have shown that exposure frequently reduces yield in grain crops by decreasing ear and pod numbers, seed numbers per ear, spikelet or pod (and hence seed number per plant), and individual seed weight (Table 4).…”

“…By contrast, Grunwald & Endress (1988) noted that the protein content of seeds was unaffected in soybean, but the oil content was reduced following exposure ; reductions in oil content have also been reported for oilseed rape (Bosac et al, 1998 ;. Decreases in soluble carbohydrate or solids have been noted for both grain (oilseed rape ; Bosac et al, 1998) and fruit crops (watermelon, Gimeno et al, 1989Gimeno et al, , 1990Gimeno et al, , 1999. In Lima bean (Phaseolus lunatus), exposure to ozone increased the concentrations of nitrogen and several essential amino acids in the seed (Meredith et al, 1986), while the calcium, magnesium, potassium and phosphorus content of the grain was increased in spring wheat (Fuhrer et al, 1990).…”

“…The importance of such information has been demonstrated by recent monitoring studies which show that the ambient ozone climate exceeds the threshold for potential reductions in crop yield over large areas of Europe and North America (Fowler et al, 1999). There is abundant evidence that current ambient ozone concentrations in many industrialized areas of the world are sufficient to induce significant yield losses in both agricultural and native species (Heagle et al, 1988 ;Heck et al, 1988 ;Mulchi et al, 1988 ;Heagle, 1989 ;Pleijel et al, 1991 ;De Temmerman et al, 1992 ;Fuhrer et al, 1992 ;Ja$ ger et al, 1993 ;Ska$ rby et al, 1993 ;Vandermeiren et al, 1995, Mulholland et al, 1997a, 1998aDavison & Barnes, 1998 ;Lyons & Barnes, 1998 ;Bergweiler & Manning, 1999 ;Gimeno et al, 1999 ;. However, although evidence is accumulating to suggest that the composition of native communities may be affected, there is still relatively little information available concerning the effects of ozone on the reproductive performance of native tree and herbaceous species (Davison & Barnes, 1998 ;Barnes et al, 1999a).…”

Radish plant behaviour under short-term elevated ozone fumigation

“…High O 3 concentrations have long been known to affect many physiological and biochemical characteristics, as well as growth and yield of agricultural crops [4][5][6] and natural vegetation [7][8][9]. It is generally assumed that damage by O 3 is mainly the result of reactive oxygen species formation, promoting oxygen toxicity in the plant cell [10].…”