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Title: Carbon allocation and partitioning in aspen clones varying in sensitivity to tropospheric ozone

Author: Coleman, M.D.; Dickson, R.E.; Isebrands, J.G.; Karnosky, D.F.;

Date: 1995

Source: Tree Physiology 15, 593-604

Publication Series: Miscellaneous Publication

Description: Clones of aspen (Populus tremuloides Michx.) were identified that differ in biomass production in response to O3exposure. 14Carbon tracer studies were used to determine if the differences in biomass response were linked to shifts in carbon allocation and carbon partitioning patterns. Rooted cuttings from three aspen Clones (216, O3 tolerant; 271, intermediate; and 259, O3 sensitive) were exposed to either charcoal-filtered air (CF) or an episodic, two-times-ambient O3 profile (2x) in open-top chambers. Either recently mature or mature leaves were exposed to a 30-min 14C pulse and returned to the treatment chambers for a 48-h chase period before harvest. Allocation of 14C to different plant parts, partitioning of 14C into various chemical fractions, and the concentration of various chemical fractions in plant tissue were determined. The percent of 14C retained in recently mature source leaves was not affected by O3 treatment, but that retained in mature source leaves was greater in O3-treated plants than in CF-treated plants. Carbon allocation from source leaves was affected by leaf position, season, clone and O3 exposure. Recently mature source leaves of CF-treated plants translocated about equal percentages of 14C acropetally to growing shoots and basipetally to stem and roots early in the season. When shoot growth ceased (August 16), most 14C from all source leaves was translocated basipetally to stem and roots. At no time did mature source leaves allocate more than 6% of 14C translocated within the plant to the shoot above. Ozone effects were most apparent late in the season. Ozone decreased the percent 14C translocated from mature source leaves to roots and increased the percent 14C translocated to the lower stem. In contrast, allocation from recently mature leaves to roots increased. Partitioning of 14C among chemical fractions was affected by O more in source leaves than in sink tissue. In source leaves, more 14C was incorporated into the sugar, organic acid and lipids + pigments fractions, and less 14C was incorporated into starch and protein fractions in O3-treated plants than in CF-treated plants. In addition, there were O3 treatment interactions between leaf position and clones for 14C incorporation into different chemical fractions.

When photosynthetic data were used to convert percent 14C transported to the total amount of carbon transported on a mass basis, it was found that carbon transport was controlled more by photosynthesis in the source leaves than proportional changes in allocation to the sinks. Ozone decreased the total amount of carbon translocated to all sink tissue in the O3-sensitive Clone 259 because of decreases in photosynthesis in both recently mature and mature source leaves. In contrast, O3 had no effect on carbon transport from recently mature leaves to lower shoots of either Clone 216 or 271, had no significant effect on transport to roots of Clone 216, and increased transport to roots of Clone 271. The O3-induced increase in transport to roots of Clone 271 was the result of a compensatory increase in upper leaf photosynthesis and a relatively greater shift in the percent of carbon allocated to roots. In contrast to those of Clone 271, recently mature leaves of Clone 216 maintained similar photosynthetic rates and allocation patterns in both the CF and O3 treatments. We conclude that Clone 271 was more tolerant to O3 exposure than Clone 216 or 259. Tolerance to chronic O3 exposure was directly related to maintenance of high photosynthetic rates in recently mature leaves and retention of lower leaves.

Keywords: air pollution, carbohydrates, photosynthesis, Populus tremuloides

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Coleman, M.D.; Dickson, R.E.; Isebrands, J.G.; Karnosky, D.F. 1995. Carbon allocation and partitioning in aspen clones varying in sensitivity to tropospheric ozone. Tree Physiology 15, 593-604


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