The effect of elevated CO₂ on diel leaf growth cycle, leaf carbohydrate content and canopy growth performance of Populus deltoides

Abstract

Image sequence processing methods were applied to study the effect of elevated CO 2 on the diel leaf growth cycle for the first time in a dicot plant. Growing leaves of Populus deltoides, in stands maintained under ambient and elevated CO 2 for up to 4 years, showed a high degree of heterogeneity and pronounced diel variations of their relative growth rate (RGR) with maxima at dusk. At the beginning of the season, leaf growth did not differ between treatments. At the end of the season, final individual leaf area and total leaf biomass of the canopy was increased in elevated CO 2 . Increased final leaf area at elevated CO 2 was achieved via a prolonged phase of leaf expansion activity and not via larger leaf size upon emergence. The fraction of leaves growing at 30-40% day À1 was increased by a factor of two in the elevated CO 2 treatment. A transient minimum of leaf expansion developed during the late afternoon in leaves grown under elevated CO 2 as the growing season progressed. During this minimum, leaves grown under elevated CO 2 decreased their RGR to 50% of the ambient value. The transient growth minimum in the afternoon was correlated with a transient depletion of glucose (less than 50%) in the growing leaf in elevated CO 2 , suggesting diversion of glucose to starch or other carbohydrates, making this substrate temporarily unavailable for growth. Increased leaf growth was observed at the end of the night in elevated CO 2 . Net CO 2 exchange and starch concentration of growing leaves was higher in elevated CO 2 . The extent to which the transient reduction in diel leaf growth might dampen the overall growth response of these trees to elevated CO 2 is discussed.

Synchronous high-resolution phenotyping of leaf and root growth in Nicotiana tabacum over 24-h periods with GROWMAP-plant

“…We speculate that the observed diel leaf RGR pattern, which does not follow the Type 1 growth pattern described in older plants of N. tabacum , may be specific to the early seedling stage. Such developmental influence on diel leaf growth is also supported by the earlier observations in poplar leaves [40], showing an increase of diel growth amplitudes with progressing season (low amplitudes in early summer, high amplitudes towards autumn), although this was not accompanied by a substantial change in the timing of maxima and minima of the diel leaf growth pattern.…”

Growth of Eastern Cottonwoods (Populus deltoides) in elevated [CO2] stimulates stand‐level respiration and rhizodeposition of carbohydrates, accelerates soil nutrient depletion, yet stimulates above‐ and belowground biomass production

“…Canopy expansion and increased aboveground biomass in 800 and 1200 ppm treatments presumably contributed to increases in stand respiration as the season progressed. Enhanced production of leaves with a smaller SLA (evidently reflecting the higher starch content; Walter et al , 2005) was presumably responsible for enhanced canopy respiration (Davey et al , 2004).…”

Functional dynamics of plant growth and photosynthesis – from steady‐state to dynamics – from homogeneity to heterogeneity

“…The timing of leaf growth during the day differs considerably between plant species and presumably reflects the integration of the particular photosynthetic resource capture and redistribution (source–sink) properties of the species. While a number of plants such as Ricinus communis (Walter, Feil & Schurr 2002) or Nicotiana tabacum (Walter & Schurr 2005) show maximal leaf growth at dawn, Populus deltoides grows strongest at dusk (Walter et al . 2005; Matsubara et al .…”

“…2005) affect only the amplitude but neither the phasing nor the shape of the diel course of leaf expansion. In contrast, plants growing in elevated atmospheric CO 2 concentrations showed a transient growth reduction in the afternoon in growing cottonwood leaves, which was not present when plants were grown in ambient CO 2 concentrations (Walter et al . 2005).…”

“…1998). Walter et al . (2005) showed that elevated CO 2 supply increased photosynthesis in growing leaves, temporarily depleted carbohydrate pools and changed the diurnal pattern of leaf growth.…”