Changes in gas exchange characteristics during the life span of giant sequoia: implications for response to current and future concentrations of atmospheric ozone

Abstract

Native stands of giant sequoia (Sequoiadendron giganteum Bucholz) are being exposed to relatively high concentrations of atmospheric ozone produced in urban and agricultural areas upwind. The expected change in environmental conditions over the next 100 years is likely to be unprecedented in the life span (about 2,500 years) of giant sequoia. We determined changes in physiological responses of three age classes of giant sequoia (current-year, 12-, and 125-year-old) to differing concentrations of ozone, and assessed age-related differences in sensitivity to pollutants by examining physiological changes (gas exchange, water use efficiency) across the life span of giant sequoia (current-year, 2-, 5-, 20-, 125-, and > 2,000-year-old trees). The CO(2) exchange rate (CER) was greater in current-year (12.1 micro mol CO(2) m(-2) s(-1)) and 2-year-old seedlings (4.8 micro mol CO(2) m(-2) s(-1)) than in all older trees (3.0 micro mol CO(2) m(-2) s(-1), averaged across the four older age classes). Dark respiration was highest for current-year seedlings (-6.5 +/- 0.7 micro mol CO(2) m(-2) s(-1)) and was increased twofold in symptomatic individuals exposed to elevated ozone concentrations. Stomatal conductance (g(s)) was greater in current-year (355 mmol H(2)O m(-2) s(-1)) and 2-year-old seedlings (200 mmol H(2)O m(-2) s(-1)) than in all older trees (50 mmol H(2)O m(-2) s(-1)), indicating that the ozone concentration in substomatal cavities is higher in young seedlings than in trees. Significant changes in water use efficiency, as indicated by C(i)/C(a), occurred in trees between ages 5 and 20 years. We conclude that giant sequoias seedlings are sensitive to atmospheric ozone until they are about 5 years old. Low conductance, high water use efficiency, and compact mesophyll all contribute to a natural ozone tolerance, or defense, or both, in foliage of older trees.

A general method of parameterizing the big‐leaf model to predict the dry‐canopy evaporation rate of individual coniferous forest stands

“…Although the relationship between h and reference G s values is empirical at this stage, the decline in G s with increasing h agrees with ecophysiological studies at the leaf-and crown-scale level (e.g. Grulke and Miller, 1994;Schoettle, 1994;Ryan et al, 1997;Hubbard et al, 1999;Tyree, 2003). These ecophysiological studies showed a decline in stomatal and crown conductances.…”

Impacts of ozone on trees and crops

“…Most comparisons of seedlings vs. mature trees showed greater ozone sensitivity in seedlings, including red spruce (Rebbeck and Jensen 1993), sequoias (Grulke and Miller 1994), and black cherry (Fredericksen et al 1996). Greater ozone sensitivity in seedlings was attributed to larger stomatal conductances in all of these cases.…”

“…Jensen and Roberts (1986) also showed higher ozone sensitivity under more humid atmospheric conditions due to higher stomatal conductance. Under future conditions of higher CO 2 fertilization, it is possible that ozone damage will be reduced due to lower stomatal conductance (Grulke andMiller 1994, Fiscus et al 2005). …”

Ambient ozone effects on forest trees of the eastern United States: a review

“…Lower conductance and ozone uptake contributed to less foliar ozone sensitivity in mature vs. seedling giant sequoia (Sequoidendron giganteum Bucholz.) (Grulke & Miller, 1994). Visible injury, stomatal conductance and leaf ozone uptake were greater in open-grown black cherry seedlings than in sun leaves of mature trees (Fredericksen et al, 1996 b).…”