2 The effect of elevated CO2 and climatic extremes on plant growth

2.1 Plant structures: leaves and roots

CO2 enrichment of the air in which crops grow usually stimulates their growth and yield. Plant structure and physiology are usually markedly altered; this includes increased leaf expansion and cell wall extensibility and often cell turgor pressure, leading to increased leaf and root growth. If increased turgor pressure is alone insufficient to account for increases in leaf growth under elevated CO2, then cell wall relaxation (extensibility), cell division or both may also be affected.

Simplistically, scientists have suggested that increased leaf size, if associated with larger cells, suggests that cell expansion has been stimulated, whilst increased leaf size, if associated with more cells, suggests that cell division has been stimulated.

However, various studies have reported differences in the various cellular mechanisms driving leaf expansion, which can vary between species and seasons; thus, one or other mechanisms may play a larger role, but this is beyond this introductory unit. Similar studies have focused on roots and such similar mechanisms for increased root length and/or biomass under conditions of elevated CO2.

1 The greenhouse effect and climatic extremes

2.2 Seasonal growth