Altering young tomato plant growth by nitrate and CO2 preserves the proportionate relation linking long-term organic-nitrogen accumulation to intercepted radiation

A previously published model of crop nitrogen (N) status based on intercepted photosynthetically active radiation (R-i, mol per plant) suggested that plant organic N accumulation is related to R-i by a constant ratio, defined hereafter as the radiation use efficiency for N (NRUE). The aim of this paper was to compare the effects of N nutrition and CO2 enrichment on NRUE and RUE (radiation use efficiency for biomass accumulation). In three unrelated glasshouse experiments, tomato plants (Solanum lycopersicum) grown in hydroponics were fed for 28 d (exponential growth) with full solutions containing constant NO3- concentrations ([NO3-]) ranging from 0.05 to 15 mol m(-3), both under ambient or CO2-enriched (1000 mu l l(-1)) air. Each experiment comprised five harvests. Low [NO3-] (< 0.3 mol m(-3)) limited growth via leaf area (LA) restriction and decreased light interception. CO2 enrichment enhanced dry weight and LA. RUE was not affected by [NO3-], but increased under CO2-enriched air. By contrast, NRUE was not affected by [NO3-] or CO2 enrichment. It is suggested that the radiation efficiency for organic N acquisition (NRUE) did not depend on C or N nutrition for young plants grown under unstressed conditions.