Seasonal response of slash pine (Pinus elliottii var. elliottii Engelm.) photosynthesis to long‐term exposure to ozone and acidic precipitation*

Abstract

summary Four half‐sib families of slash pine (Pinus elliottii var. elliottii) were planted in open‐top chambers and exposed to ozone and simulated acidic precipitation (3: 7 molar ratio of nitric and sulphuric acids). The 4 ozone treatments were (1) charcoal‐filtered air, (2) unfiltered ambient air, (3) twice ambient and (4) three times ambient ozone, with treatments applied 12 h per day, 11 months per year for 28 months. Seedlings were irrigated weekly with one of three rain acidities: pH 33, 4.3 or 5.3 at a total rainfall equivalent of 133 cm per year. Photosynthetic rates were measured approximately every 10 weeks, on the most recently emerged branches each year. In 1988 the 3rd flush was measured, and in 1989 and 1990 the 1st flush of each year was measured. Elevated ozone concentrations generally reduced photosynthetic rates, especially during the summer months, but there was no evidence of either a threshold dose or a simple linear relationship between photosynthesis and ozone exposure. There was a seasonal drop in photosynthetic rates from March to September each year. An ontogenetic decrease in photosynthesis was also evident as trees matured. Stomatal conductance also decreased as the needles aged. Seedlings irrigated with pH 3.3 solution typically exhibited the highest photosynthetic rates, presumably due to a fertilizer effect.

Diurnal water relations and gas exchange of two slash pine (Pinus elliottii) families exposed to chronic ozone levels and acidic rain *

“…They found that as tbe leaf area of a plant increases during canopy development, leaf conductance decreases on a unit leaf area basis as canopy transpiration approaches a maximum. We might see an ozone effect on this hydraulic coordination in slash pine because both leaf area and g,, of trees exposed to 2X and 3X ozone tended to be lower than in the trees in the CF and NF treatments (Byres et al 1992a; Figs 3, 4). This suggests that the ozone treatments might be reducing the hydraulic capacity of the roots and stems which, in turn, is affecting the equihbrium level of the co-ordination proposed by Meinzer & Grantz (1991).…”

“…Similar results and conclusions were reported for poplars exposed to ozone (Reich & Lassoie, 1984). By contrast, Chappelka, Chevone & Seiler (1988), using multiple regression analysis on data for young yellow-poplar (Liriodendron tulipifera) seedlings, reported that the slope for the VPD parameter was increased in the ozone treatment. They interpreted this as an increased sensitivity of the stomata to VPD.…”

“…2) and smaller leaf area in trees in the 3X ozone chambers (3 vs. 4 7m^; Byres, Dean & Johnson, 1992a). Temple (1990) found no effect on seasonal water use by cotton {Gossypium hirsutum) exposed to ozone, but reported that ozone significantly decreased water use efficiency (measured as seed yield per unit water lost).…”

“…Pearson and Mansfield (1993) found that ozone reduced leaf conductance of Fagus syhatica under watered conditions whereas needle conductance remained higher under imposed drought conditions. In a longer-term study with Norway spruce (P. abies), elevated ozone reduced stomatal conductance in the light and increased it in the dark, and excised needles were found to dry more rapidly than control needles (Barnes, Eamus & Brown, 1990). Reich & Lassoie (1984) reported that ozone-treated hybrid poplar (Populus deltoides x trichocarpa) exhibited diminished stomatal control of water loss and faster wilting of excised treated leaves.…”

“…Recently, reduced growth of natural Reports of reduced forest health and productivity slash and loblolly pine {Pinus elliottii and P. taeda, from central Europe and northeastern United States respectively) stands in southeastern L^nited States have been related to anthropogenic pollution (see has been attributed to air pollution along with several other factors, acting singly or in combination » Journal Series R-n3O75 of the lnstnute of Food and (Sheffield et al. 1985;Sheffield & Cost, 1987 , accelerating needle senescence and abscission (Byres, , altering carbon allocation between shoots and roots (Adams et al, 1990), and decreasing photosynthesis (Sasek & Richardson, 1989;Byres, Johnson & Dean, 19926). These responses and others have heen related to altered stomatal physiology in many plant species (Reich, 1987;Darrall, 1989).…”