METHODS AND APPLICATIONS TO CONTROL THE UPTAKE RATE OF CARBON

Methods to control carbon and nutrient uptake at different availabilit y 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 plant s. Steady-state comprises, by definition, equality between constant re lative 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, R(AC). I n the second method (b), a constant concentration of CO2 in the air, c (a), was used to attain non-limiting conditions. The methods are analo gous to those used by us to control plant nutrition, and the generalit y of fluxes to quantify supply as well as uptake and growth was verifi ed. Thus, different R(AC) resulted suited in clear-cut responses, from strong reduction to non-limitation of uptake and growth, whereas diff erent c(a) levels in the range 100 to 700 ppm had comparatively small effects, with an unclear causality. Non-limiting conditions were achie ved at c(a) greater than or equal to 200 ppm. Effects reported in the literature have been based upon the control of c(a), similarly to meth od (b), whereas results comparable to those obtained with method (a) a re lacking. Transpiration rate increased rapidly at c(a) < 200 ppm CO2 , and at low R(AC) levels, less than or equal to 0.1 day(-1), wilting tendencies were observed. Elevated c(a) 500 or 700 ppm, did not increa se the relative growth rate (R(G)) but reduced transpiration and incre ased both nitrogen productivity (growth rate per unit of nitrogen in t he plant) and transpiration productivity (growth rate per unit of wate r transpired by the plant). Obviously, effects of c(a) may be due to c hanged transpiration rate rather than to changed quantitative availabi lity of CO2. Relative uptake (R(OC)) and growth (R(G)) rates were clos ely equal to the R(AC) applied (R(AC) approximate to R(UC) approximate to R(G)); i.e., the purely mathematical conditions defining steady-st ate were fulfilled. This unambiguous and straightforward test of relia bility confirms that experimental artefacts did not produce uncontroll ed or unintended effects, so that the new technique allows an accurate control of CO2 uptake and plant growth. The results add to previous d atabases and reference systems, where limiting conditions grade and cl assify 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.