Increased root growth in elevated CO2: a biophysical analysis of root cell elongation

Abstract

A biophysical analysis of root expansion was conducted in four chalk downland herbs (Sanguisorba minor Scop., Lotus corniculatus L., Anthyllis vul-neraria L. and Plantago media L.) exposed to either ambient or elevated CO2in controlled environment cabinets. Measurements of fine (F) and extra-fine (EF) root extension rate (RER), water relations, and cell wall tensiometric extensibility revealed differences in the diurnal pattern of root growth between species. After 35 d of exposure to elevated CO2, RER of both F and EF roots increased significantly in darkness and on illumination for S. minor, whilst for A. vulneraria (EF roots only) and L. corniculatus a significant increase occurred at night whereas for P. media a significant increase occurred during the day. Cells measured in the zone of elongation were longer in all species exposed to elevated CO2. Water potential ({Psi}), solute potential ({Psi}), turgor pressure (P), yield turgor (Y) and effective turgor (Pe) were measured by stress-relaxation of excised root tips placed in psychro-meters. Solute potentials decreased significantly for all species following exposure to elevated CO2. In S. minor and L. corniculatus, P and Pe, respectively, were higher in elevated CO2. No significant effects of CO2 on Y were observed (not shown). Root cell wall tensiometric extensibility, measured as % plasticity, increased in all species exposed to elevated CO2. These results suggest that root growth is enhanced following increased cell expansion and that increased P and cell wall tensiometric extensibility are both important for root growth in elevated CO2.