Elevated CO₂and plant structure: a review

Abstract

Summary Consequences of increasing atmospheric CO2 concentration on plant structure, an important determinant of physiological and competitive success, have not received sufficient attention in the literature. Understanding how increasing carbon input will influence plant developmental processes, and resultant form, will help bridge the gap between physiological response and ecosystem level phenomena. Growth in elevated CO2 alters plant structure through its effects on both primary and secondary meristems of shoots and roots. Although not well established, a review of the literature suggests that cell division, cell expansion, and cell patterning may be affected, driven mainly by increased substrate (sucrose) availability and perhaps also by differential expression of genes involved in cell cycling (e.g. cyclins) or cell expansion (e.g. xyloglucan endotransglycosylase). Few studies, however, have attempted to elucidate the mechanistic basis for increased growth at the cellular level. Regardless of specific mechanisms involved, plant leaf size and anatomy are often altered by growth in elevated CO2, but the magnitude of these changes, which often decreases as leaves mature, hinges upon plant genetic plasticity, nutrient availability, temperature, and phenology. Increased leaf growth results more often from increased cell expansion rather than increased division. Leaves of crop species exhibit greater increases in leaf thickness than do leaves of wild species. Increased mesophyll and vascular tissue cross‐sectional areas, important determinates of photosynthetic rates and assimilate transport capacity, are often reported. Few studies, however, have quantified characteristics more reflective of leaf function such as spatial relationships among chlorenchyma cells (size, orientation, and surface area), intercellular spaces, and conductive tissue. Greater leaf size and/or more leaves per plant are often noted; plants grown in elevated CO2 exhibited increased leaf area per plant in 66% of studies, compared to 28% of observations reporting no change, and 6% reported a decrease in whole plant leaf area. This resulted in an average net increase in leaf area per plant of 24%. Crop species showed the greatest average increase in whole plant leaf area (+ 37%) compared to tree species (+ 14%) and wild, nonwoody species (+ 15%). Conversely, tree species and wild, nontrees showed the greatest reduction in specific leaf area (– 14% and – 20%) compared to crop plants (– 6%). Alterations in developmental processes at the shoot apex and within the vascular cambium contributed to increased plant height, altered branching characteristics, and increased stem diameters. The ratio of internode length to node number often increased, but the length and sometimes the number of branches per node was greater, suggesting reduced apical dominance. Data concerning effects of elevated CO2 on stem/branch anatomy, vital for understanding potential shifts in functional relationships of leaves with stems, roots with stems, and leaves with roots, ar...

Physiological and molecular alterations in plants exposed to high [CO2] under phosphorus stress

“…increasing the root-to-shoot ratio (Ceulemans and Mousseau, 1994;Rogers et al, 1996;Pritchard et al, 1999;Rogers et al, 1999). However, some studies reported decreased rootto-shoot ratio (Salsman et al,1999;McMaster et al, 1999) in response to high [CO 2 ] while others did not observe any significant effect (Mo et al, 1992;Ferris and Taylor, 1993;Chaudhuri et al,1990;Obrist and Arnone, 2003).…”

Growth and crown architecture of two aspen genotypes exposed to interacting ozone and carbon dioxide

“…In general, elevated CO 2 has been found to increase primary production, unless other resources were limiting (Saxe et al ., 1998;Körner, 2003), and to shift plant resource allocation towards the roots, whereas elevated O 3 diminished net carbon uptake and typically reduced root rather than shoot growth (Andersen, 2003). In addition, elevated CO 2 and O 3 regimes were found to induce changes in crown and root architecture because of modification of branching patterns (Pritchard et al ., 1999;Dickson et al ., 2001). Hence, elevated CO 2 and O 3 were used as stressors to provoke differential changes in growth and allocation between settings of intra-and inter-specific competition in order to more readily distinguish relevant mechanisms in tree competitiveness (Grams et al ., 2002;Matyssek et al ., 2002).…”

Spatial and Temporal Effects of Free-Air CO2Enrichment (POPFACE) on Leaf Growth, Cell Expansion, and Cell Production in a Closed Canopy of Poplar

“…It is still unknown whether forests of the future will maintain a higher leaf area index (LAI), as implied from smalltree studies (Ceulemans et al, 1997) or whether the long-term (decades) responses will be reduced allocation to foliage and lower LAI, as suggested by some modeling approaches (Medlyn and Dewar, 1996) or involve acclimation to limited nitrogen (Oren et al, 2001). Leaf growth is often stimulated in short-term response to elevated [CO 2 ] (Taylor et al, 1994;Pritchard et al, 1999), and both leaf cell expansion and cell production are sensitive to [CO 2 ] (Taylor et al, 1994). It is likely that these processes respond to additional carbohydrate from photosynthesis and, as such, altered atmospheric [CO 2 ] provides a critical insight into how carbon regulates plant development and growth (Masle, 2000).…”

“…Leaf growth is often stimulated in short-term response to elevated [CO 2 ] (Taylor et al, 1994;Pritchard et al, 1999), and both leaf cell expansion and cell production are sensitive to [CO 2 ] (Taylor et al, 1994). It is likely that these processes respond to additional carbohydrate from photosynthesis and, as such, altered atmospheric [CO 2 ] provides a critical insight into how carbon regulates plant development and growth (Masle, 2000).…”