Photosynthetic responses of loblolly pine (Pinus taeda) needles to experimental reduction in sink demand

David A. Myers, Richard B. Thomas, Evan H. Delucia

Research output: Contribution to journalArticle

Abstract

Sink strength in loblolly pine (Pinus taeda L.) was experimentally manipulated on two sun-exposed branches on each of two neighboring trees by excising the emerging terminal cohort (second flush of 1996) during a period of rapid needle expansion. In addition, export of photosynthate was restricted on one of these branches from each tree by removal of bark and phloem just below the second flush of 1995. Treatment-induced changes in needle biochemistry were measured in 3-month-old (first flush of 1996) and 1-year-old (final flush of 1995) needles collected 1,5 and 8 days after treatment. In 3-month-old needles, sugar concentration increased by 24% one day after leader excision, and increased by 86% on Day 8 after leader excision and girdling. Starch concentration increased by 33% in 3-month-old needles on Day 1 after leader excision, and by 400% in l-year-old needles on Day 8 after leader excision and girdling. Physiological changes in 3-month-old and 1-year-old needles were measured by open-flow gas exchange and chlorophyll fluorescence on Day 8 after leader excision and girdling. Light- and CO 2 -saturated net photosynthesis decreased following treatment in both 3-month-old and 1-year-old needles (23 and 17%, respectively). Maximum rate of carboxylation (V(cmax)) decreased by 25% in 3-month-old needles and by 31% in 1-year-old needles in response to leader excision and girdling. The combined treatment resulted in a 38% decrease in maximum rate of electron transport (J(max)) in 3-month-old needles and a 37% decrease in J(max) in 1-year-old needles. Before leader excision and girdling, 2% oxygen in air stimulated photosynthesis by 17 to 19%, but this stimulation was only 3 to 4% at 9 days after treatment. These physiological responses indicate that experimentally lowered sink strength resulted in rapid feedback inhibition of leaf-level photosynthetic capacity in loblolly pine.

Original languageEnglish (US)
Pages (from-to)235-242
Number of pages8
JournalTree Physiology
Volume19
Issue number4-5
DOIs
StatePublished - Apr 1999

Fingerprint

Pinus taeda
girdling
Needles
strength (mechanics)
photosynthesis
carboxylation
photosynthates
physiological response
biochemistry
phloem
electron transfer
Photosynthesis
gas exchange
bark
starch
fluorescence
sugars
chlorophyll
oxygen
air

Keywords

  • Girdling
  • Rapid feedback inhibition
  • Sink source
  • Sink strength
  • Terminal leader excision

ASJC Scopus subject areas

  • Physiology
  • Plant Science

Cite this

Photosynthetic responses of loblolly pine (Pinus taeda) needles to experimental reduction in sink demand. / Myers, David A.; Thomas, Richard B.; Delucia, Evan H.

In: Tree Physiology, Vol. 19, No. 4-5, 04.1999, p. 235-242.

Research output: Contribution to journalArticle

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abstract = "Sink strength in loblolly pine (Pinus taeda L.) was experimentally manipulated on two sun-exposed branches on each of two neighboring trees by excising the emerging terminal cohort (second flush of 1996) during a period of rapid needle expansion. In addition, export of photosynthate was restricted on one of these branches from each tree by removal of bark and phloem just below the second flush of 1995. Treatment-induced changes in needle biochemistry were measured in 3-month-old (first flush of 1996) and 1-year-old (final flush of 1995) needles collected 1,5 and 8 days after treatment. In 3-month-old needles, sugar concentration increased by 24{\%} one day after leader excision, and increased by 86{\%} on Day 8 after leader excision and girdling. Starch concentration increased by 33{\%} in 3-month-old needles on Day 1 after leader excision, and by 400{\%} in l-year-old needles on Day 8 after leader excision and girdling. Physiological changes in 3-month-old and 1-year-old needles were measured by open-flow gas exchange and chlorophyll fluorescence on Day 8 after leader excision and girdling. Light- and CO 2 -saturated net photosynthesis decreased following treatment in both 3-month-old and 1-year-old needles (23 and 17{\%}, respectively). Maximum rate of carboxylation (V(cmax)) decreased by 25{\%} in 3-month-old needles and by 31{\%} in 1-year-old needles in response to leader excision and girdling. The combined treatment resulted in a 38{\%} decrease in maximum rate of electron transport (J(max)) in 3-month-old needles and a 37{\%} decrease in J(max) in 1-year-old needles. Before leader excision and girdling, 2{\%} oxygen in air stimulated photosynthesis by 17 to 19{\%}, but this stimulation was only 3 to 4{\%} at 9 days after treatment. These physiological responses indicate that experimentally lowered sink strength resulted in rapid feedback inhibition of leaf-level photosynthetic capacity in loblolly pine.",
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