Contrasting effects of elevated CO2 on the root and shoot growth of four native herbs commonly found in chalk grassland.

Abstract

The aim of this study was to investigate the impact of ambient (345 μl l-1 ) and elevated (590 μl l-1 ) CO2 on the root and shoot growth of four native chalk grassland herbs: Sanguisorba minor Scop, (salad burnet), Lotus carniculatus L. (birdsfoot trefoil), Anthyllis vulneraria L. (kidney vetch) and Plantago media L. (hoary plantain). Elevated CO2 had contrasting effects on both shoot and root growth of the four species studied. Both leaf expansion and production were stimulated by elevated CO2 for S. minor, L. corniculatus and P. media, whilst for A. vulneraria, only leaflet shape appeared to be altered by elevated CO2 , with the production of broader leaflets, compared with those produced in ambient CO2 . After 100 d shoot biomass was enhanced in elevated CO2 for S. minor and L. corniculatus, whilst there was no effect of elevated CO2 on shoot biomass for A. vulneraria or P. media. Contrasting effects of CO2 were also apparent for measurements of specific leaf area (SLA), which increased for L. corniculatus, decreased for A. vulneraria and remained unaltered for S. minor and P. media in elevated compared with ambient CO2 . Elevated CO2 also had contrasting effects on both the growth and morphology of roots. The accumulation of root biomass was stimulated following exposure to elevated CO2 for S. minor and L. corniculatus whilst there was no effect on root biomass for A. vulneraria or P. media. Root length was measured on three occasions during the 100 d and revealed that exposure to elevated CO2 promoted root extension in S. minor, L. corniculatus and P. media, but not in A. vulneraria. Specific root length (SRL, length per unit dry weight) was increased in elevated CO2 for one species, P. media, whilst the root to shoot ratio of all four species remained unchanged by CO2 . These results show that four native herbs differ in their response to CO2 , suggesting that the structure of this plant community may be altered in the future.