Methods and applications to control the uptake rate of carbon

Abstract

Methods to control carbon and nutrient uptake at different availability of carbon were tested on plants of birch (Betula pendula Roth.) and tomato (Lycopersicon esculentum Mill. cv. Solentos). The present paper accounts for the methods and the possibility to maintain steady‐state, i.e., a long‐term and stable physiological state of acclimated plants. Steady‐state comprises, by definition, equality between constant relative growth rates, and relative uptake rates of carbon and nutrients. Two methods were tested. The first, not previously applied, method (a), was based on a constant relative addition rate of carbon, RAC. In the second method (b), a constant concentration of CO2 in the air, ca, was used to attain non‐limiting conditions. The methods are analogous to those used by us to control plant nutrition, and the generality of fluxes to quantify supply as well as uptake and growth was verified. Thus, different RAC resulted in clear‐cut responses, from strong reduction to non‐limitation of uptake and growth, whereas different ca levels in the range 100 to 700 ppm had comparatively small effects, with an unclear causality. Non‐limiting conditions were achieved at ca≥ 200 ppm. Effects reported in the literature have been based upon the control of ca, similarly to method (b), whereas results comparable to those obtained with method (a) are lacking.Transpiration rate increased rapidly at ca < 200 ppm CO2, and at low RAC levels, ≤ 0.1 day−1, wilting tendencies were observed. Elevated ca, 500 or 700 ppm, did not increase the relative growth rate (RG) but reduced transpiration and increased both nitrogen productivity (growth rate per unit of nitrogen in the plant) and transpiration productivity (growth rate per unit of water transpired by the plant). Obviously, effects of ca may be due to changed transpiration rate rather than to changed quantitative availability of CO2.Relative uptake (RUC) and growth (RG) rates were closely equal to the RAC applied (RAC≅ RUC≅ RG); i.e., the purely mathematical conditions defining steady‐state were fulfilled. This unambiguous and straightforward test of reliability confirms that experimental artefacts did not produce uncontrolled or unintended effects, so that the new technique allows an accurate control of CO2 uptake and plant growth. The results add to previous databases and reference systems, where limiting conditions grade and classify plant performance as deviations from maximum growth. Evidently, methodology in experimentation and in evaluation of plant responses, can be based upon unifying concepts and general theories.