Mild ozone exposure alters 14C dynamics in foliage of Pinus taeda L.

Abstract

To explore the physiological mechanisms underlying ozone-induced growth reductions in loblolly pine (Pinus taeda L.), seedlings were exposed to sub-ambient (charcoal-filtered), ambient or twice-ambient ozone in open-top chambers for three growing seasons. In the final year of exposure, current-year needle fascicles were labeled with (14)CO(2) and the incorporation of (14)C into biochemical fractions was followed for 48 hours. Irrespective of ozone treatment, losses of (14)C-assimilates from foliage to respiration and translocation were minimal during the first 3 hours, whereas more than 60% of the label was lost during the next 45 hours. Radiolabel in sugar decreased rapidly after a lag period, roughly paralleling the pattern of total (14)C loss. The amount of (14)C label in starch and lipids plus pigments remained constant throughout the 48-hour chase period, whereas the amount of (14)C label in other fractions showed a net decrease over the 48-hour chase period. Ozone treatments altered foliar carbon dynamics in two ways: (1) ozone exposure increased foliar (14)C retention up to 21% for the first 5 hours after labeling, but not thereafter, and (2) ozone exposure decreased partitioning of (14)C into starch and increased partitioning of (14)C into organic acids, residue, and lipids plus pigments, indicating an intensified partitioning of carbon to injury and repair processes. Both short-term carbon retention and diversion of carbon from storage compounds to repair processes are foliar mechanisms by which ozone exposure could decrease growth in loblolly pine seedlings.

Carry-over effects of ozone and water stress on leaf phenological characteristics and bud frost hardiness of Fagus crenata seedlings

“…In our previous studies, it was reported that net photosynthetic rate, starch grain size in chloroplasts and whole-plant dry mass of F. crenata seedlings were reduced by the exposure to O 3 (Yonekura et al 2001a, b). The exposure to O 3 caused the partition of assimilated carbon into organic acid rather than into starch (Friend and Tomlinson 1992). Therefore, the O 3 -induced reductions in the concentrations of carbohydrates and elements in the leaves of F. crenata seedlings are considered to be mainly due to the reduction of net photosynthesis and CO 2 fixation, and the inhibition in the amount of assimilated carbon partitioned into starch and protein.…”

Influence of elevated ozone and limited nitrogen availability on conifer seedlings in an open‐air fumigation system: effects on growth, nutrient content, mycorrhiza, needle ultrastructure, starch and secondary compounds

“…1990 ; Amundson et al . 1991 ; Friend & Tomlinson 1992; Kainulainen et al . 1994 ) of conifers in growth chamber experiments after higher O 3 exposure concentrations than used in the present study.…”

“…Also, accumulation of starch following exposure to O 3 has been reported ( Luethy‐Krause & Landolt 1990). Friend & Tomlinson (1992) concluded that O 3 ‐induced decrease in foliar starch concentration could be a result of decreased allocation of current photosynthate to starch or increased mobilization of starch pools. They also suggested that foliar starch could be a promising indicator of O 3 stress because it was sensitive to short‐term fluctuations in O 3 concentrations.…”

Deciphering the ozone-induced changes in cellular processes: a prerequisite for ozone risk assessment at the tree and forest levels

“…Since O 3 reduces carbon gain by limiting stomatal diffusion, lowering Rubisco activity, inducing early senescence and increasing carbon cost for tissue repair and antioxidant synthesis, it drastically decreases source strength and carbon availability for export to sink tissues. Additionally, increased soluble sugar content and carbohydrate retention have been observed in source tissue exposed to chronic O 3 concentration (from 0 to 110 ppb) (Friend and Tomlinson 1992;Grantz and Farrar 1999;Grantz and Yang 2000), suggesting a decrease in carbon export under O 3 . A lower leaf sucrose export and higher carbohydrate level would lead to feedback regulation of photosynthesis and therefore partly explain the reduction in carbon assimilation.…”