SUMMARYMicroclimatic factors interact during ozone episodes to influence the sensitivity of plants to ozone and thus arc likely to modify the amount of injury development. This paper investigates these interactions in an ozone-sensitive cultivar of clover {Trifolium subterraneum cv. Geraldton). Experiments were conducted using a glasshouse-based closed-chamber exposure system in which the plants were exposed for 7 h to either chareoal-filtered air {CF) or CF plus ozone at concentrations ranging from 40 to 160 ppb. The microclimatic conditions inside the chambers ranged from 16 to 36 °C, 0-9-3'6 kPa vapour pressure deficit (VPD), and 80--460 /imol m~'^ s"^ Photosynthetically Active Radiation (PAR). Seven days after ozone exposure, the extent of foliar ozone itijun.-was scored visually. The assessment scoring system was validated by pigment analysis. The data from these exposures were analysed using artificial neural networks (ANNs), the principles of which are described in tbe paper. Two ANNs were used, one to investigate the efTeets of microclimate on the threshold AOT40 (dose accumulated above a threshold of 40 ppb) above wbich injury developed, tbe other to determine the extent of visible injury development. Both networks used temperature, VPD, PAR and AOT40 as inputs. Testing with previously unseen data showed that the networks produced accurate predictions of the threshold and extent of injury for a range of ozone doses and microclimatic conditions. For example, the injury score network predicted that at 100 /(mol m"^ s"' PAR and 1 kPa VPD an AOT40 of 3. SO ppb h was required to produce an injury score of 1, wbereas in conditions of 400 /imol m"'' s"^ PAR and 3-5 kPa VPD, an AOT40 of 460 ppb h was required. Analysis of the weightings of components of the trained networks indicated that VPD and PAR had a stronger influence on the response to ozone than did temperature. Furthermore, this approach revealed that microclimate had a greater influence on the extent of ozone injury than on the threshold for injury.

SUMMARYIn 1988, open-top chambers (OTCs) based on the Raleigh (USA) design were used to investigate the effect of ambient pollutants on field-sown Viciafaba cv, Ticol. This paper reports an aspect of this study in which the effect of the chamber itself on crop growth and development was investigated. Non-filtered chamber (NF OTC) microclimates were typically 0-8 °C warmer, with 20 % less radiation and reduced wind speeds compared with open-field sub-plots (AA treatments). These differences are sufficient to induce alterations in the growth and development of V. faba.Plant development progressed more quickly inside the chambers in response to the faster accumulation of thermal time. Chamber-grown V.faba were up to 20 cm taller and had fewer branches (0-7 compared with 1-2 per plant) than plants grown in the AA treatments. Larger leaf areas developed on the NF plants, and there were fewer stomata per unit leaf area in this treatment (34 compared with 42 mm"^ P = 0-01). Enclosure within an OTC did not alter the number of fiowers per plant or the number of flowers which formed pods. However, at harvest, chamber-grown plants had a 13% higher yield than the plants grown in open-field plots. These differences in growth are described in relation to the microclimate differences between AA and NF treatments.

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Summary The uptake, movement and metabolism of fluroxypyr* is compared in two contrasting weed species, Stellaria media (susceptible) and Viola arvensis (moderately resistant). Similar rates of uptake occurred in both species, with a rapid cuticular uptake of 50% of that applied within 4 h. Total uptake by the underlying leaf tissue reached 66.6% and 70.8% in S. media and V. arvensis after 7 days. In translocation studies, in which 14C‐fluroxypyr was applied to previously sprayed plants, 5.1% of applied 14C‐activity was translocated from the treated leaves of S. media after 1 day, which increased to 42.2% after 7 days, recovered mainly from the stem tissue. In V. arvensis translocation was similar after 24 h however, after 7 days over 40% of applied 14C‐activity remained in the treated leaves and only 9.7% was translocated, mainly to the developing leaves and apical tissue. 14C‐activity extracted from the cuticle was the methylheptyl ester of fluroxypyr in both species. In the treated leaves and apical tissue, 14C‐activity was the free acid of fluroxypyr and polar conjugates with a significantly greater proportion of the acid in S. media. It is concluded that the resistance or V. arvensis is partially due to reduced translocation and greater conjugation than in the susceptible S. media.

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