Effects of Long-Term Ozone Exposure and Soil Moisture Deficit on Growth of a Ladino Clover-Tall Fescue Pasture

Consistent ozone-induced decreases in pasture forage quality across several grassland types and consequences for UK lamb production

“…Reductions in the legume fraction, but not the grass fraction, of harvested biomass as a result of ozone exposure have been demonstrated using both intact managed pasture (Fuhrer, 1994, Trifolium repens -Lolium perenne mixtures established in field conditions from seed (Wilbourn et al, 1995), and T. repens -L. perenne established in mesocosms (Hayes et al, 2009). Similarly, reductions in the clover:grass ratio due to ozone have been reported by Nussbaum et al (1995) and Heagle et al (1989) using T. repens and L. perenne and T. repens and Festuca arundinacea respectively, which can also occur if the above-ground biomass of the grass component increases due to reduced competition from the legume content. Reductions in N-fixation in clover in response to increasing ozone concentrations have also been shown (Hewitt et al, 2014), implying a reduced nitrogen content of the clover component of the pasture.…”

Effects of ozone on wild plants

“…Therefore the effects of management would be expected to depend on the balance between the effects of lower competition in a cut sward and increased exposure to ozone. Most experiments on species mixtures have employed several cuts in a season Heagle et al, 1989 ;Kohut, Laurence & Amundsen, 1988 ;Rebbeck, Blum & Heagle, 1988 ;Fuhrer et al, 1994 ;Nussbaum, Geissmann & Fuhrer, 1995 ;Pleijel et al, 1996) grass\forb mixtures in OTCs and employed two cutting treatments ; cut every 2 wk and cut only once at the end of the season. The percentage of the two forbs (Trifolium repens and Veronica chamaedrys) in the harvested biomass declined with ozone concentration in both cutting treatments but the striking feature of the experiment was that the cutting regime had a far greater effect than even the highest ozone exposure (Fig.…”

“…In this situation there are many ways in which ozone and water deficit might interact. Heggestad et al (1985) provided evidence that ozone reduces tolerance to soil moisture deficit, but many papers on crops report little or no ozone-water deficit interaction Miller et al, 1988 ;Heagle et al, 1989 ;Temple, 1990 ;Fangmeier et al, 1994), whilst some show that water deficit reduces the effects of ozone. There are, for example, reports of reduced visible injury (Pell et al, 1993 ;Vandermieren et al, 1995), lower ozoneinduced stress ethylene production (Tingey et al, 1982), reduced effects on net photosynthesis Vozzo et al, 1995), reduced water consumption (Kobayashi et al, 1993) and alleviation of effects on yield (Temple, Taylor & Benoit, 1985 ;Heagle et al, 1987 ;Moser et al, 1988 ;.…”

“…competition modifies the physiological and ecological amplitude of species so the ecological effects of ozone have to be investigated in this context. The most comprehensive information available is for simple grass\clover mixtures (Bennett & Runeckles, 1977 ;Kochhar et al, 1980 ;Montes, Blum & Heagle, 1982 ;Blum et al, 1983 ;Kohut et al, 1988 ;Rebbeck et al, 1988 ;Becker et al, 1989 ;Heagle et al, 1989Heagle et al, , 1991Fuhrer et al, 1994 ;Nebel & Fuhrer, 1994 ;Nussbaum et al, 1995 ;Wilbourn et al, 1995 ;' Pleijel et al, 1996). The subject has been reviewed recently by Fuhrer (1997).…”

Plant–plant interactions and soil moisture might be important in determining ozone impacts on grasslands

“…For instance, soil moisture, cutting frequency and ozone-exposure patterns have been shown to modify ozone effects on species mixtures (Heagle et al, 1989 ;Nussbaum et al, 1995). It is necessary to understand the nature of and to quantify these interactions in order to improve predictions about the possible effects of increased ozone concentrations, and to define critical levels of ozone for significant effects on plant community composition.…”