Photosynthetic acclimation to elevated CO₂ is modified by source:sink balance in three component species of chalk grassland swards grown in a free air carbon dioxide enrichment (FACE) experiment

Abstract

Artificial chalk grassland swards were exposed to either ambient air or air enriched to 600 µmol mol -1 CO 2 , using free-air CO 2 enrichment technology, and subjected to an 8 week simulated grazing regime. After 14 months of treatment, ribulose-1,5-bisphosphate carboxylase (Rubisco) activity (V c,max ) and electron transport mediated ribulose-1,5-bisphosphate (RuBP) regeneration capacity (J max ), estimated from leaf gas exchange, were significantly lower in fully expanded leaves of Anthyllis vulneraria L. (a legume) and Sanguisorba minor Scop. grown in elevated CO 2 . After a change in source:sink balance brought about by defoliation, photosynthetic capacity was fully restored in A. vulneraria and S. minor, but acclimation continued in the grass Bromopsis erecta (Hudson) Fourr. Changes in net photosynthesis (P n ) with growth at elevated CO 2 ranged from a 1·6% reduction in precut leaves of A. vulneraria to a 47·1% stimulation in postcut leaves of S. minor. Stomatal acclimation was observed in leaves of A. vulneraria (reduced stomatal density) and B. erecta (reduced stomatal conductance). The results are discussed in terms of whole-plant resource-use optimization and chalk grassland community competitive interactions at elevated CO 2 .

Carbon dioxide effects on stomatal responses to the environment and water use by crops under field conditions

“…1 Reductions in leaf stomatal conductance with a doubling of the current atmospheric carbon dioxide concentration ( [CO 2 ]) for three vegetation types differing in the aerodynamic coupling between the canopy and the atmosphere, and the resulting hypothetical reductions in canopy transpiration. Reductions in leaf stomatal conductance are: (1) for crops, the area-weighted mean value from Table 1, (2) for native herbaceous vegetation, a mean value from Bryant et al (1998), Lauber and Korner (1997) and Lee et al (2001); and (3) for forests, a mean value from the reviews of Curtis and Wang (1998) and Medlyn et al (2001). Average coupling factors for the vegetation types were obtained from Jarvis and McNaughton (1986).…”

“…Crops are major consumers of fresh water resources, so that any changes in crop water use with rising atmospheric [CO 2 ] would have important environmental and economic impacts. Crops also have among the largest reductions in stomatal conductance at elevated [CO 2 ] of any vegetation type (e.g., Bryant et al 1998;Curtis and Wang 1998;Pataki et al 2000).…”

Carbon source–sink limitations differ between two species with contrasting growth strategies

“…Despite this well‐developed ecological theory, we do not currently know the extent to which slower growth in perennials than annuals arises from greater source to sink limitation. Experimental manipulations of the source:sink ratio provide insights into the relative contributions of source and sink processes to growth rate and may be achieved through a variety of techniques including sink removal (Arp ), genetic modification (Ainsworth et al , Weichert et al ; Zuther et al ), source removal (von Caemmerer & Farquhar , Bryant et al ; Rogers et al ; Eyles et al ), inhibiting resource export from the source (Ainsworth & Bush ) and increasing source activity using elevated CO 2 (Kinsman et al ; Masle ), reviewed by White et al (). Here, we alter the atmospheric CO 2 concentration ([CO 2 ]) to non‐invasively manipulate the source:sink ratio in barley – elevated [CO 2 ] to increase the source strength and sub‐ambient [CO 2 ] to decrease it – with current [CO 2 ] as a reference against which to compare the source manipulations.…”

Does Free-Air Carbon Dioxide Enrichment Affect Photochemical Energy Use by Evergreen Trees in Different Seasons? A Chlorophyll Fluorescence Study of Mature Loblolly Pine1

“…Acclimatory losses of Rubisco or capacity for RubP regeneration have been observed in situ under elevated p CO 2 (e.g. Gunderson and Wullschleger, 1994;Oechel et al, 1994;Curtis, 1996;Bryant et al, 1998;Rogers et al, 1998) and would complicate this conceptual model.…”