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

Abstract

summary Seedlings from two half‐sib families of Pinus elliottii var. elliottii Engelm. differing in sensitivity to ozone were grown in open‐top chambers for 22 months under simulated acidic rain (pH 3‐3) and four concentrations of ozone. The ozone concentrations were: charcoal‐filtered air (CF); non‐filtered ambient air (NF); twice the NF level (2X), thrice the NF level (3X). Ozone exposures were computer controlled to follow diurnal and seasonal fluctuations in ambient ozone concentrations. On two days, 24 April and 29 May, in the spring of 1990, trees were sampled repeatedly for xylem water potential, needle conductance and photosynthesis from sunrise to sunset on the oldest needle age class attached to the main stem (first needle cohort produced in 1989, and therefore, exposed the longest to ozone). On 30 May, three needle age classes (first age class of 1989, the last age class of 1989 and first ape class of 1990) were sampled over the day for needle conductance in trees exposed to CF and 3X ozone. Soil moisture measurements indicated that the 3X trees used significantly more water from the 75–l00 cm soil depth even though leaf area on these trees was about 30% less. Tree response showed very consistent xylem water potential among sample days, families and ozone treatments. By contrast, needle conductance and photosynthetic rate showed significant ozone and family differences. In addition, the response of needle conductance to vapour pressure deficit lessened as ozone exposure increased. The putative ozone‐sensitive family (106‐56) exhibited less needle conductance in the 2X and 3X treatments as well as reduced photosynthesis on both sample days, suggesting prior ozone injury. The youngest needle age class of this same family when exposed to 3X ozone showed higher needle conductance in the afternoon which could lead to both excessive water loss and uptake of ozone. The interactive effects of chronic ozone exposure, limited soil moisture and genetics altered the water relations and gas exchange of slash pine growing in north Florida. Changes in sromatal conductance along with possible adjustments in the hydraulic properties of the roots and stems appeared to be responsible for the control of water potentials in trees of differing sizes and leaf area. The importance of the contribution of different needle age classes to the water and carbon economy of slash pine, and their modification by cumulative ozone exposure, cannot he overlooked in interpreting air pollution effects on evergreen trees.

Variability in the carbon isotopic composition of foliage carbon pools (soluble carbohydrates, waxes) and respiration fluxes in southeastern U.S. pine forests

“…The empirical analysis of Oren et al [1999] shows a consistent and robust relationship between stomatal conductance at low D and the sensitivity of the stomatal closure response to increasing D. This analysis indicates that individuals, species, and stands with low stomatal conductance at low D exhibit a lower sensitivity to D [ Oren et al , 1999]. Thus, the lack of a clear response of δ C ER to D in this study is consistent with physiological studies in seedlings [ Johnson et al , 1995] and mature trees [ Teskey et al , 1994] that find a limited influence of D on net photosynthesis and stomatal conductance in P. elliottii and P. palustris [ Gonzalez‐Benecke et al , 2011]. This limited influence of D is further supported by a limited variability in δ C SC (Figure 3b) despite large variations in D during the study period (Figures 2a and 2c).…”

“…The error bars indicate the standard error of Keeling plots intercepts. [Johnson et al, 1995] and mature trees [Teskey et al, 1994] that find a limited influence of D on net photosynthesis and stomatal conductance in P. elliottii and P. palustris [Gonzalez-Benecke et al, 2011]. This limited influence of D is further supported by a limited variability in dC SC (Figure 3b) despite large variations in D during the study period (Figures 2a and 2c).…”

Ozone effects on seedling sugar maple (Acer saccharum) and yellow-poplar (Liriodendron tulipifera): gas exchange

“…Little information is available on the diurnal response of woody plants exposed to O 3 . Johnson et al (1995) measured the diurnal gas exchange of slash pine (Pinus elliottii Engelm. ), grown in open-top chambers and exposed to four concentrations of O 3 (ranging from CF to 3× ambient O 3 ).…”