Elsevier

Environmental Pollution

Volume 115, Issue 3, December 2001, Pages 463-472
Environmental Pollution

Increased leaf area expansion of hybrid poplar in elevated CO2. From controlled environments to open-top chambers and to FACE

https://doi.org/10.1016/S0269-7491(01)00235-4Get rights and content

Abstract

We examined the response of hybrid poplar to elevated CO2 in contrasting growth environments: controlled environment chamber (CE), open-top chamber (OTC) and poplar free air CO2 enrichment (POPFACE) in order to compare short versus long-term effects and to determine whether generalisations in response are possible for this fast growing tree. Leaf growth, which for poplar is an important determinant of stemwood productivity was followed in all environments, as were the determinants of leaf growth—cell expansion and cell production. Elevated CO2 (550–700 μmol mol−1, depending on environment) resulted in an increase in final leaf size for Populus trichocarpa×Populus deltoides (Populus×interamericana) and P. deltoides×Populus nigra (Populus×euramericana), irrespective of whether plants were exposed during a short-term CE glasshouse study (90 days), a long-term OTC experiment (3 years) or during the first year of a POPFACE experiment. An exception was observed in the closed canopy POPFACE experiment, where final leaf size remained unaltered by CO2. Increased leaf extension rate was observed in elevated CO2 in all experiments, at some point during leaf development, as determined by leaf length. Again the exception were the POPFACE experiment, where effects were not statistically significant. Leaf production and specific leaf area (SLA) were increased and decreased, respectively, on five out of six occasions, although both were only statistically significant on two occasions and interestingly for SLA never in the FACE experiment. Although both cell expansion and cell production were sensitive to CO2 concentration, effects appeared highly dependent on growth environment and genotype. However, increased leaf cell expansion in elevated CO2 was often associated with changes in the biophysical properties of the cell wall, usually increased cell wall plasticity. This research has shown that enhanced leaf area development was a consistent response to elevated CO2 but that the magnitude of this response is likely to decline, in long-term exposure to elevated CO2. Effects on SLA and leaf production suggest that CE and OTC experiments may not always provide good predictors of the ‘qualitative’ effects of elevated CO2 in long-term ecosystem experiments.

Introduction

When plants are exposed to elevated atmospheric carbon dioxide, photosynthesis and the accumulation of plant biomass are often increased in the short-term (Woodward, 1992, Pritchard et al., 1999). Whether this effect is maintained during long-term exposure of forest trees will depend, at least in part, on growing conditions (including nitrogen supply) and on the interactions and feedback between root and soil processes (Norby et al., 1999). In order to understand these complex feedbacks it is necessary to undertake large, field-scale exposures and for forest trees, these free-air CO2 enrichment (FACE) experiments are only now being used (http://oden.nrri.umn.edu/factssii/; Hendrey et al., 1999, Ferris et al., 2001, Norby et al., 2001). Generalisations are therefore difficult, but species with rapid, continuous growth may not become 'sink limited' and could maintain a positive response to CO2 (Arp, 1991, Farrar & Williams, 1991). Such responsive species are often characterised by increased leaf area development, from either lamina expansion or from the production of new leaves, or both (Taylor et al., 1994).

The genus Populus may be unusual for a woody plant in this respect, showing a large positive response to elevated CO2 with little evidence that this effect diminishes with time (Ceulemans et al., 1995a, Ceulemans et al., 1995b, Gardner, 1995, Taylor et al., 1995). This is in contrast to other woody species, such as Quercus for example, where long-term growth responses are thought to decline (Hättenschwiler et al., 1997), although past experiments on Populus have tended to be short-term using controlled environment (CE) and open top chamber (OTC) exposure systems. Leaf growth in poplar trees is an important determinant of total tree productivity and so an understanding of leaf growth physiology in elevated CO2 is warranted. Such studies usually occur in one type of growing environment, for example, in CE chambers (Taylor et al., 1995) or in a field system such as OTCs (Curtis et al., 1990), or FACE (Norby et al., 2001) with few studies aimed at comparing responses or validating each individual approach. In a recent review, Norby et al. (1999) claimed that OTC experiments have provided qualitatively similar and valid results, although quantitatively, they may be inadequate in explaining ecosystem response to elevated CO2, since they have only characterised the initial positive, although possibly transitory, response. However, it is possible that for long-lived trees, even this ‘qualitative’ consensus may be absent, but there are very few experiments on which to examine this contention.

Highly mechanistic studies of leaf growth in elevated CO2 have been undertaken and have shown that leaf growth in elevated CO2 is stimulated following enhanced cell expansion (Ranasinghe and Taylor, 1996) resulting from enhanced cell wall loosening and extensibility, associated with an increase in the activity of the wall loosening enzyme xyloglucan endo-transyglycosylase. The importance of such mechanistic explanations for increased leaf growth in elevated CO2 remains largely unknown but in a recent paper it was confirmed that enhanced leaf cell expansion and increased leaf size do contribute to rapid growth, even in a FACE (POPFACE) exposure (Ferris et al., 2001).

The overall objective of this study was to quantify the effect of exposure to elevated CO2 on leaf growth of hybrid poplar and to determine the effects of exposure technique, plant size and plant age on these responses. In particular, this paper aimed to (1) quantify the effect of elevated CO2 on leaf area development in three growing environments, and (2) determine whether short-term experiments provide useful indicators of long-term responses to elevated CO2, and whether mechanisms are similar in different environments.

Section snippets

Materials and methods

The contrasting experimental approaches are summarised in Table 1 illustrating the similarity between the experiments (clonal material, measurements performed) as well as their difference and complementarity (contrasting growth and exposure techniques, different duration of treatments, number of replicates and time periods for measurements).

Results

Fig. 1a–f illustrate the effects of elevated CO2 on leaf extension rate (LER) for P.×interamericana and P.×euramericana hybrids grown in either OTCs, CEs or POPFACE. For both hybrids and in all environments there was a stimulation of leaf extension rate (LER) in elevated CO2 although for the clone Robusta, LER was extremely small and no significant effects were detected. Leaf growth was most rapid in the CEs, an effect most pronounced for the P.×euramericana trees (Fig. 1c). Fig. 1 also

Discussion

This study has highlighted a number of important and consistent effects of elevated CO2 following exposure in either controlled environment glasshouse, open top chambers or FACE. In addition, some contrasting responses to elevated CO2 were also observed. A central finding was the consistent effect of elevated CO2 on LER, which for poplars is closely linked to stemwood productivity (Ridge et al., 1986, Barigah et al., 1994). LER was stimulated in elevated CO2 and this response occurred in all

Acknowledgements

This research was supported financially by the EC through its Environment R & D programme at the University of Antwerp, Belgium (Contract No. EV57-CT92-0127) and at the University of Southampton (Contract No. ENV4-CT97-0657, POPFACE) and by the BBSRC BAGEC Programme (PG085/0524). The support from the British–Flemish Academic Research Collaboration programme (British Council grant No. 26/94) is gratefully acknowledged. Further financial support was provided by the Fund for Scientific Research,

References (38)

  • P.S. Curtis et al.

    Elevated atmospheric CO2 effects on below-ground processes in C3 and C4 estuarine marsh communities

    Ecology

    (1990)
  • B.G. Drake et al.

    More efficient plants: a consequence of rising atmospheric CO2

    Annual Review of Plant Physiology and Molecular Biology

    (1997)
  • J.F. Farrar et al.

    The effects of increased atmospheric carbon dioxide and temperature on carbon partitioning, source-sink relations and respiration

    Plant, Cell and Environment

    (1991)
  • R. Ferris et al.

    Elevated CO2, water relations and biphysics of leaf extension in four chalk grassland herbs

    New Phytologist

    (1994)
  • R. Ferris et al.

    Contrasting CO2 and temperature effects on leaf growth of perennial ryegrass in spring and summer

    Journal of Experimental Botany

    (1996)
  • R. Ferris et al.

    Leaf area is stimulated in Populus by free air CO2 enrichment (POPFACE), through increased cell expansion and production

    Plant, Cell and Environment

    (2001)
  • S.D.L. Gardner et al.

    Leaf growth of hybrid poplar following exposure to elevated CO2

    New Phytologist

    (1995)
  • J.P. Gaudillere et al.

    Short-term effects of CO2 enrichment on leaf development and gas exchange of young poplars (Populus euramericanaa)

    Acta Oecologia

    (1989)
  • B. Gielen et al.

    Leaf area dynamics in a closed poplar plantation under free air CO2 enrichment

    Tree Physiology

    (2001)
  • Cited by (38)

    • Estimating the response of tomato (Solanum lycopersicum) leaf area to changes in climate and salicylic acid applications by means of artificial neural networks

      2012, Biosystems Engineering
      Citation Excerpt :

      Therefore, LA strongly influences crop growth, development rate, yield potential, radiation use efficiency, and water and nutrient use (Bhatt & Chanda, 2003). When plants are exposed to elevated atmospheric CO2, radiation, and temperature, photosynthesis and the accumulation of plant biomass are often increased affecting significantly the LA development (Taylor et al., 2001). Exogenous application of elicitors is effective in present-day agricultural practices, allowing the crops to be grown successfully under different stress conditions (Hussain, Malik, Farroq, Ashraf, & Cheema, 2008).

    • Establishment and two-year growth of a bio-energy plantation with fast-growing Populus trees in Flanders (Belgium): Effects of genotype and former land use

      2012, Biomass and Bioenergy
      Citation Excerpt :

      More research on the rate of leaf production and individual leaf area is required to clarify both strategies. Total leaf area determines the amount of carbon uptake and has been previously suggested as a good indicator of biomass yield of an SRC with poplar [47–49]. In this study, LAImax was indeed found to be a good determinant of above-ground biomass production, assessed through VI.

    • Estimation of leaf area for large scale phenotyping and modeling of rose genotypes

      2012, Scientia Horticulturae
      Citation Excerpt :

      Growing conditions also influenced accuracy of estimation of area. Leaf size and shape can be influenced by climate conditions such as light intensity, temperature or CO2 concentration (e.g. De Swart et al., 2004; Ferris et al., 2001; Marcelis, 1993; Heuvelink and Marcelis, 1996; Nilwik, 1981; Taylor et al., 2001, 2003; Thomas and Bazzaz, 1996). However, in our experiment, the relative bias over environments was rather small, which might be due to the fact that the experiment was performed in only Dutch glasshouses (Table 1).

    • Spring leaf flush in aspen (Populus tremuloides) clones is altered by long-term growth at elevated carbon dioxide and elevated ozone concentration

      2010, Environmental Pollution
      Citation Excerpt :

      Two climate change factors that alter leaf growth and productivity are increasing atmospheric carbon dioxide concentration ([CO2]) and increasing tropospheric ozone concentration ([O3]) (Taylor et al., 2001; Ainsworth and Long, 2005; Karnosky et al., 2005; Wittig et al., 2009).

    View all citing articles on Scopus
    View full text