Root Respiration and Growth in Plantago major as Affected by Vesicular-Arbuscular Mycorrhizal Infection

Effects of vesicular-arbuscular mycorrhizal (VAM) infection and P on root respiration and dry matter allocation were studied in Plantago major L. ssp. pleiosperma (Pilger). By applying P, the relative growth rate of non-VAM controls and plants colonized by Glomus fasciculatum (Thaxt. sensu Gerdemann) Gerdemann and Trappe was increased to a similar extent (55-67%). However, leaf area ratio was increased more and net assimilation rate per unit leaf area was increased less by VAM infection than by P addition. The lower net assimilation rate could be related to a 20 to 30% higher root respiration rate per unit leaf area of VAM plants. Root respiration per unit dry matter and specific net uptake rates of N and P were increased more by VAM infection than by P addition. Neither the contribution of the alternative respiratory path nor the relative growth rate could account for the differences in root respiration rate between VAM and non-VAM plants. It was estimated that increased fungal respiration (87%) and ion uptake rate (13%) contributed to the higher respiratory activity of VAM roots of P. major.