Abstract

Photosynthetic rates of plants grown in natural systems exhibit diurnal patterns often characterized by an afternoon decline, even when measured under constant light and temperature conditions. Since we thought changes in the carbohydrate status could cause this pattern through feedback from starch and sucrose synthesis, we studied the natural fluctuations in photosynthesis rates of plants grown at 36 and 56 Pa CO2 at a FACE (free-air-CO2-enrichment) research site. Light-saturated photosynthesis varied by 40% during the day and was independent of the light-limited quantum yield of photosynthesis, which varied little through the day. Photosynthesis did not correspond with xylem water potential or leaf carbohydrate build-up, but rather with diurnal changes in air vapor-pressure deficit and light. The afternoon decline in photosynthesis also corresponded with decreased stomatal conductance and decreased Rubisco carboxylation efficiency which in turn allowed leaf-airspace CO2 partial pressure to remain constant. Growth at elevated CO2 did not affect the afternoon decline in photosynthesis, but did stimulate early-morning photosynthesis rates relative to the rest of the day. Plants grown at 56 Pa CO2 had higher light-limited quantum yields than those at 36 Pa CO2 but, there was no growth-CO2 effect on quantum yield when measured at 2 kPa O2. Therefore, understory plants have a high light-limited quantum yield that does not vary through the day. Thus, the major diurnal changes in photosynthesis occur under light-saturated conditions which may help understory saplings maximize their sunfleck-use-efficiency.

Original languageEnglish (US)
Pages (from-to)39-49
Number of pages11
JournalNew Phytologist
Volume145
Issue number1
DOIs
StatePublished - Jan 1 2000

Fingerprint

Photosynthesis
saplings
understory
photosynthesis
carbon dioxide
Light
Quantum yield
Carbohydrates
Carboxylation
Ribulose-Bisphosphate Carboxylase
xylem water potential
carbohydrates
Air Pressure
Vapor Pressure
Xylem
saturated conditions
air
Partial Pressure
carboxylation
ribulose-bisphosphate carboxylase

Keywords

  • Acer rubrum
  • Cercis canadensis
  • Diurnal variation
  • Elevated CO
  • FACE
  • Liquidambar styraciflua
  • Photosynthesis
  • Understory

ASJC Scopus subject areas

  • Physiology
  • Plant Science

Cite this

Diurnal regulation of photosynthesis in understory saplings. / Singsaas, Eric L.; Ort, Donald R.; DeLucia, Evan H.

In: New Phytologist, Vol. 145, No. 1, 01.01.2000, p. 39-49.

Research output: Contribution to journalArticle

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