Growth and respiration in plants from various adaptation groups as affected by mineral nutrient deficiency

The effect of the deficiency in mineral nutrients was investigated in plant species representing various adaptation groups (stress-tolerant, competiti ve, and ruderal plants). Dry and fresh weight, as well as the length of sho ots and underground organs, were determined in 20- to 50-day-old seedlings. The ratio between the dry weights of shoot and root (SRR), relative growth rate (RGR), the rate of total dark respiration (SigmaR), gross photosynthe sis (P-g), and the proportion of the respiratory expenditures to gross phot osynthesis (SigmaR/P-g) were calculated. When affected by a deficiency in m ineral nutrients, the weight of the whole plant decreased. In resistant spe cies of clover (Trifolium pratense L.) and alfalfa (Medicago sativa L.), th is reduction was insignificant, whereas, in the ruderal species amaranth (A maranthus retroflexus L.), it was at its highest. In all the species invest igated, the ratio SigmaR/P-g was 38-46%. Under stress conditions, this inde x increased. Given a deficiency in mineral nutrients, the changes in SRR, R GR, and SigmaR/P-g were greater in amaranth, suggesting that this plant spe cies is less tolerant to stress. The correlation between RGR and SigmaR obs erved in amaranth under normal conditions indicates that the major energy e xpenditures are associated with growth. Under stress conditions, such a cor relation was not observed. In more resistant species of clover and alfalfa, a weak positive correlation between RGR and SigmaR was observed both under normal and stress conditions. In these species, the deficiency in mineral nutrients probably brought about a reduction in the growth component of tot al dark respiration and a rise in the adaptation component. The complex of indices (SigmaR/P-g, RGR, and SRR) and the extent of their variation in the seedlings describe the potential productivity and resistance of particular species to a deficiency in mineral nutrients and may characterize the adap tation type of the plants.