Contributions of diffusional limitation, photoinhibition and photorespiration to midday depression of photosynthesis in Arisaema heterophyllum in natural high light

Hiroyuki Muraoka, Yanhong Tang, Ichiro Terashima, Hiroshi Koizumi, Izumi Washitani

Research output: Contribution to journalArticle

83 Citations (Scopus)

Abstract

Diurnal changes in photosynthetic gas exchange and chlorophyll fluorescence were measured under full sunlight to reveal diffusional and non-diffusional limitations to diurnal assimilation in leaves of Arisaema heterophyllum Blume plants grown either in a riparian forest understorey (shade leaves) or in an adjacent deforested open site (sun leaves). Midday depressions of assimilation rate (A) and leaf conductance of water vapour were remarkably deeper in shade leaves than in sun leaves. To evaluate the diffusional (i.e. stomatal and leaf internal) limitation to assimilation, we used an index [1-A/A350], in which A350 is A at a chloroplast CO2 concentration of 350 μmol mol-1. A350 was estimated from the electron transport rate (J(T)), determined fluorometrically, and the specificity factor of Rubisco (S), determined by gas exchange techniques. In sun leaves under saturating light, the index obtained after the 'peak' of diurnal assimilation was 70% greater than that obtained before the 'peak', but in shade leaves, it was only 20% greater. The photochemical efficiency of photosystem II (ΔF/F(m)) and thus J(T) was considerably lower in shade leaves than in sun leaves, especially after the 'peak'. In shade leaves but not in sun leaves, A at a photosynthetically active photon flux density (PPFD) > 500 μmol m-2 s-1 depended positively on J(T) throughout the day. Electron flows used by the carboxylation and oxygenation (J(O)) of RuBP were estimated from A and J(T). In sun leaves, the J(O)/J(T) ratio was significantly higher after the 'peak', but little difference was found in shade leaves. Photorespiratory CO2 efflux in the absence of atmospheric CO2 was about three times higher in sun leaves than in shade leaves. We attribute the midday depression of assimilation in sun leaves to the increased rate of photorespiration caused by stomatal closure, and that in shade leaves to severe photoinhibition. Thus, for sun leaves, increased capacities for photorespiration and non-photochemical quenching are essential to avoid photoinhibitory damage and to tolerate high leaf temperatures and water stress under excess light. The increased Rubisco content in sun leaves, which has been recognized as raising photosynthetic assimilation capacity, also contributes to increase in the capacity for photorespiration.

Original languageEnglish
Pages (from-to)235-250
Number of pages16
JournalPlant, Cell and Environment
Volume23
Issue number3
DOIs
Publication statusPublished - 2000
Externally publishedYes

Keywords

  • Arisaema heterophyllum
  • Chlorophyll fluorescence
  • Leaf gas exchange
  • Light acclimation
  • Midday depression
  • Photoinhibition
  • Photorespiration
  • Photosynthesis (CO assimilation)
  • Stomata

ASJC Scopus subject areas

  • Plant Science

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