Lockyer, D. R. 1985. The effect of sulphur dioxide on the growth of Lolium perenne L., Lolium multiflorum Lam., Dactylis glomerata L., and Phleum pratense L.—J. exp. Bot. 36: 1851-1859. Four agriculturally important grasses, Lolium perenne L., Lolium multiflorum Lam., Dactylis glomerata L. and Phleum pratense L. were exposed to sulphur dioxide (S02) in a system of exposure chambers. The plants were exposed for a total of 43 d to mean concentrations of S02 in the air of 0,87 or 448 pg m~3 and herbage was harvested twice. All four grasses showed chlorotic lesions after exposure to the highest concentration of S02. The effect of S02 on the yield of herbage was statistically significant only at the second harvest and at the highest concentration; the dry weights of shoots of D. glomerata and L. perenne were reduced by 33% and 16% respectively. Significant effects of S02 were also found on the 'transpiration coefficients' measured for D. glomerata and P. pratense. The grasses differed in their uptake of sulphur from the atmosphere but this was not related to their sensitivity to S02. Total-S concentration in the shoots of L. perenne, L. multiflorum and D. glomerata increased almost linearly in response to increasing S02 concentration; with P. pratense only the highest S02 concentration raised total-S above the level in control plants. These increases were almost entirely due to the accumulation of sulphate-S. Key words—Sulphur dioxide, Lolium perenne, Lolium multiflorum, Dactylis glomerata, Phleum pratense. Correspondence to: The Animal and Grassland Research Institute, Hurley, Maidenhead, Berkshire SL6 5LR, U.K. INTRODUCTION Studies in the United Kingdom into the effects of sulphur dioxide (S02) on grasses have concentrated on Lolium perenne L. (perennial ryegrass) cv. S23. Cowling and his colleagues at the Grassland Research Institute found that, with this grass, concentrations of S02 24 weeks) to S02 concentrations of 43 and 106 jigm'3, whereas in some of their other experiments, similar or higher concentrations had no effect on yield. 1 Now the Animal and Grassland Research Institute. © Oxford University Press 1985 This content downloaded from 157.55.39.161 on Mon, 23 May 2016 04:57:21 UTC All use subject to http://about.jstor.org/terms 1852 Lockyer—Grass Growth and S02 Major discrepancies in the findings of four groups of workers studying the effects of S02 on grasses have been discussed by Bell (1982); he pointed out that comparisons between experiments are made difficult by the different procedures and apparatus used by each group. Unsworth and Mansfield (1980) also considered these discrepancies and, in considering the system of exposure chambers used at the Grassland Research Institute (Lockyer et al., 1976), they suggested that exposure concentrations may have been over-estimated because the measurements were made on air before it had entered the plant compartment. The study reported here had two main aims: (i) to examine the effect of S02 on the growth of L. perenne cv. S23, after modification of the exposure chambers to give increased turbulence and reduced boundary layer resistance to S02 flux, with S02 concentrations measured in air drawn from the plant compartment, and (ii) to compare with L. perenne the reaction of three other agriculturally important grasses, Lolium multiflorum Lam. (Italian ryegrass), Dactylis glomerata L. (cocksfoot) and Phleum pratense L. (timothy), exposed to SO 2 under the same experimental conditions. MATERIALS AND METHODS The plants were grown in soil collected from the 0-150 mm horizon of a sandy clay loam at the Grassland Research Institute, Hurley; its properties have been described elsewhere (Cowling and Jones, 1970). After thorough mixing, the soil was passed through a 6-0 mm sieve and weighed into 36 polypropylene pots of 150 mm diameter. Each pot contained 4-33 kg soil (oven-dry basis). Seeds of the following four grasses were sown, 57 per pot, with nine pots allocated at random to each grass: (i) Lolium perenne L. (cv. S23); (ii) Lolium multiflorum Lam. (tetraploid cv. 'Sabalan'); (iii) Dactylis glomerata L. (cv. S37); (iv) Phleum pratense L. (cv. S48). After emergence, the number of seedlings was reduced to 42 per pot. The surface of the soil was covered with a 10 mm layer of opaque polyethylene granules to minimize evaporation of water and the sorption of S02. Distilled water was added frequently to bring the pots to a predetermined weight and the soil water to an average tension of 7-36 kPa. The pots were kept in a heated glasshouse with a minimum temperature of 10 °C and a photoperiod of 12 h provided by mercury vapour lamps giving a minimum intensity of 30 W m"2 (visible radiation) measured 100 mm above the soil surface. Nutrients in solution were added to all pots on day 24 from sowing in the following amounts (kg"1 dry soil): 100 mg N as NH4N03,48-4 mg K and 20 mg S as K2S04,12-6 mg K and 10 mg P as KH2P04, 10 mg P as CaH4(P04)2, 5 0 mg Mg as MgCl2 and 3 0 mg Mo as (NH4)6Mo7024. In mid-March, on day 27 from sowing, four pots—one for each grass variety—were placed in each of nine exposure chambers chosen at random to provide three replicates of the following treatments: (i) no addition of S02 to the supply of filtered air; (ii) addition of SO2 to give 100 pg m " 3, and (iii) addition of S02 to give 500 pg m"3. The exposure chambers were of the type that has been fully described elsewhere (Lockyer et ai, 1976) but with one modification. As a means of increasing turbulence the perforated ceiling of each chamber was replaced by a tube of Melinex film. The tube, 80 mm in diameter and perforated with 40 holes of 5 0 mm diameter, extended from the air inlet port across the width of the chamber. With an air-flow of 700 dm3 min"1 this modification increased turbulence in the chamber and reduced boundary layer resistance to the transfer of water vapour, measured using artificial leaves as described by Sheehy and Tearle (1975), from 0-42 s cm"1 (with perforated ceiling) to 0-30 s cm" L The removal of the ceiling allowed the monitoring systems to draw air from the plant compartment and the measurements of S02 represent concentrations in air surrounding the plants, rather than, as previously, in air entering the chamber. Some aspects of this particular system of exposure chambers have been discussed elsewhere (Unsworth and Mansfield, 1980; Cowling, Lockyer, Chapman, and Koziol, 1981). While the plants were in the chambers, water use was recorded to give an estimate of transpiration. Records of temperature and relative humidity were taken daily around noon. Supplementary lighting (Philips Type HLRG, 400 W) was used to give a 16 h photoperiod with a minimum intensity of 30 W m~2 (visible radiation) measured 100 mm above the soil surface. Plant shoots were harvested for the first time on day 51 from sowing by cutting at 30 mm above the soil surface and nutrients were applied again at the original rates. A second harvest was taken at day 70 from sowing after which the stubble was cut as close as possible to the soil surface. Roots were then This content downloaded from 157.55.39.161 on Mon, 23 May 2016 04:57:21 UTC All use subject to http://about.jstor.org/terms Lockyer—Grass Growth and S02 1853 separated from the soil by sieving and washing. All plant fractions were dried for 16 h at 80 °C and weighed. Samples of shoots, stubble, and roots were analysed for total sulphur by the colorimetric method of Steinbergs, Iismaa, Freney, and Barrow (1962); sulphate in the shoots and stubble was determined by a direct digestion method (Johnson and Nishita, 1952).