Effects of long‐term ozone exposure and drought on the photosynthetic capacity of ponderosa pine (Pinus ponderosa Laws.)

Abstract

SUMMARYSeedlings of ponderosa pine {Pinus ponderosa Laws,) were grown for three years under three atmospheric ozone concentrations -clean air (CF), amhient ozone (NF), and 15 times amhient ozone (NF150)-at a moderatelypolluted site in the Sierra Nevada, under either well-watered or drought-stressed conditions. When the trees were 5 years old, photosynthetic capacities of 2-year-old, 1-year-old, and current-year needles were measured during August and September of the 3rd season of exposure. Current-year needles of NF150 trees had higher photosynthetic capacity than NF and CF trees during late summer, an effect due to greatly enhanced photosynthesis in well-watered plants that had lost older needles as a result of ozone damage. This photosynthetic compensation in well-watered NF150 seedlings was related to higher tissue nitrogen concentration in the currentyear foliage and possibly to increased inorganic phosphate cycling, hoth responses to the loss of older needles. Drought-stressed NFl 50 seedlings were partially protected from ozone damage hy decreased stomatal conductance and did not exhibit the same degree of photosynthetic compensation. No differences in photosynthetic rate were found between CF and NF seedlings or hetween well-watered and drought-stressed seedlings (across ozone treatments) in any needle age class.

Chronic drought stress reduced but not protected Shantung maple (Acer truncatum Bunge) from adverse effects of ozone (O3) on growth and physiology in the suburb of Beijing, China

“…The main possible reason was the reduction of stomatal conductance (Fig. 4) which protected the leaf from O 3 injury as reported in other research reports (Beyers et al, 1992;Wieser and Havranek, 1995). A sat was protected by drought from O 3 effects only in S4 when it was the rainy season in Beijing and high air moisture mitigated the effect of drought stress during the gas exchange measurement.…”

“…Drought stress appeared to protect plants from O 3 injury and loss mainly through its influence on reducing stomata aperture (Beyers et al, 1992;Temple et al, 1992;Wieser and Havranek, 1995); some interactions were neutral (additive). Drought didn't change O 3 damage and the effects of drought and ozone were independent in the mechanism (Pearson and Mansfield, 1994); some were synergistic and even negative.…”

Ozone and water deficit reduced growth of Aleppo pine seedlings

“…Furthermore, whole plants may compensate for small losses of leaf tissue or photosynthetic capacity with increased photosynthesis in younger undamaged leaves. For example, Beyers et al [6] found that the c needles of O 3 -exposed ponderosa pine had the highest photosynthetic rates, whereas there was no change in stomatal conductance.…”

Planning for biodiversity: bringing research and management together; Proceedings of a Symposium for the South Coast Ecoregion

“…Trees exposed to O 3 under conditions of drought stress will generally show less O 3 injury than those growing under favorable soil-water conditions because of reduced rates of gas exchange in the drought-stressed trees. This interaction between O 3 and drought has been observed both under experimental conditions (Temple andothers 1992, 1993) and in the field (Temple and Miller 1998). However, if the mechanism of stomatal closure is impaired because of O 3 injury (Grulke 1999, Patterson and Rundel 1989, Torsethaugen and others 1999) the trees may be more vulnerable to drought stress because of slow or incomplete stomatal closure.…”

“…Reduced root biomass in ponderosa pine trees chronically stressed by O 3 may also predispose O 3 -injured trees to increased susceptibility to drought stress (Grulke and others 1998). Severely O 3 -injured pines may also increase rates of stomatal conductance on remaining foliage to compensate for the loss of older annual whorls (Beyers andothers 1992, Coyne andBingham 1982). This increase in the rate of gas exchange may render these needles more susceptible to O 3 injury than needles from uninjured trees.…”