The mechanism of O 3 action on plants remains poorly characterized. Symptoms include visible lesions on the leaf surface, reduced growth and a hypothesized reduction in allocation of carbohydrate to roots. The generality of this latter phenomenon has not been demonstrated. Here, a meta-analysis is performed of all available experimental data, to test the hypotheses that O 3 exposure of the shoot inhibits biomass allocation below ground (the root/shoot allometric coefficient, k ) and inhibits whole-plant growth rate [relative growth rate (RGR)]. Both k and RGR were significantly reduced by O 3 (5.6 and 8.2%, respectively). Variability in k was greater than in RGR, and both exhibited some positive as well as mostly negative responses. The effects on k were distinct from the effects on RGR. In some cases, k was reduced while RGR was unaffected. Slow-growing plants (small RGR) exhibited the largest declines in k . These observations may have mechanistic implications regarding O 3 phytotoxicity. There were no effects of type of exposure chamber on sensitivity to O 3 . The analyses indicate that the O 3 inhibition of allocation to roots is real and general, but variable. Further experiments are needed for under-represented plant groups, to characterize exceptions to this generalization and to evaluate O 3 -environment interactions.

Summary Plants of Bellis perennis, Dactylis glomerataand Poa annua were grown from seed in controlled-environment cabinets at either 16 or 20°C; at the higher temperature all three species had increased total dry mass and leaf area when assessed on the basis of chronological time. On the basis of thermal time (summation of degree-days above 0°C; days°C) temperature decreased the dry mass in P. annua. 2. Partitioning was assessed as a change in the allometric coefficients relating shoot and root dry mass, leaf and plant mass, leaf area and plant mass, and leaf area and leaf mass. Of the 12 relationships examined only three were affected by temperature: there was increased partitioning towards the shoot relative to the root in D. glomerata and increased partitioning towards leaf area rather than leaf mass in D. glomerata and B. perennis. 3. Root respiration was unaffected by temperature of growth in D. glomerata and P. annua but was lower in B. perennis grown at elevated temperature. 4. Root respiration acclimated to temperature in P. annua and B. perennis (i.e. when measured at the same temperature, respiration was higher in plants grown at 16°C). 5. Root soluble carbohydrate concentration was unaffected by temperature of growth in any of the species. Feeding sucrose to the roots for a short period had no effect on the rate of respiration of B. perennis or D. glomerata but increased root respiration of P. annua.

We have explored the relationships between specific leaf area calculated for a whole plant and its individual leaves. Barley was grown in hydroponics in controlled environment cabinets. Plants were harvested on the basis of physiological age (defined as the number of days after full expansion of leaves on the main stem) and the area and weight of whole, fully expanded, leaves measured and specific leaf area (SLA) of individual leaves or whole plants calculated. Specific leaf area calculated for individual leaves (SLA L ) varied with leaf position and with leaf age after full expansion whereas SLA calculated for whole plants (SLA P ) varied with plant age. The same conclusions were reached whether the results were based on total dry weight or dry weight minus soluble carbohydrates (' structural weight '). Transferring plants to shade on the day of full expansion of the third leaf on the main stem increased the SLA P , and also SLA L of leaves 3 and 4 on the main stem (leaf 4 being the younger leaf of the two), because of a decrease in the ' structural weight ' of these leaves. However SLA L of leaf 2 (which was older than leaf 3) was not affected by shading ; the effect was confined to leaves developing in the new conditions.

Summary 1.We tested the hypothesis that the net partitioning of dry mass and dry mass:area relationships is unaltered when plants are grown at elevated atmospheric CO 2 concentrations. 2. The total dry mass of Dactylis glomerata, Bellis perennis and Trifolium repens was higher for plants in 700 compared to 350 µmol CO 2 mol -1 when grown hydroponically in controlled-environment cabinets. 3. Shoot:root ratios were higher and leaf area ratios and specific leaf areas lower in all species grown at elevated CO 2 . Leaf mass ratio was higher in plants of B. perennis and D. glomerata grown at elevated CO 2 . 4. Whilst these data suggest that CO 2 alters the net partitioning of dry mass and dry mass:leaf area relationships, allometric comparisons of the components of dry mass and leaf area suggest at most a small effect of CO 2 . CO 2 changed only two of a total of 12 allometric coefficients we calculated for the three species: ν relating shoot to root dry mass was higher in D. glomerata, whilst ν relating leaf area to total dry mass was lower in T. repens. 5. CO 2 alone has very little effect on partitioning when the size of the plant is taken into account.

Economics Staff Paper No. 84-11*** December 1984 *Chuck Lamberton and Gene Murra made many comments on this paper which improved the quality and presentation of the report. However, the authors are solely responsible for any remaining errors or omissions.