Carbohydrate Level and Growth of Tomato Plants

To what extent can the influence of environment on greenhouse tomato plants (Lycopersicon esculentum L.) be explained by a linear response of the growth rate to carbohydrate level? To answer this question, young tomato plants were transplanted in January and March and grown for one-month periods under natural light either with or without CO(2) enrichment to 1000 microliters per liter and either under a constant minimum temperature of 15 degrees C or a minimum temperature that fluctuated between 20 degrees C for 12 hours including the photoperiod and 10 degrees C for the remaining 12 hours. The carbohydrate levels were measured for plants under all growth conditions at several times in the diurnal cycle.At the average irradiance in January, 2.3 megajoules per square meter per day, plants under CO(2) enrichment grew 15% faster and had, on average, total nonstructural carbohydrate levels 27 milligrams per gram greater and soluble carbohydrates 3 milligrams per gram greater at all hours of the day than did plants grown under ambient CO(2). Plants grown under fluctuating diurnal temperature grew slightly faster and had total nonstructural carbohydrate levels on average 8 milligrams per gram greater than plants grown under a more constant temperature. At the average irradiance in March-April, 4.3 megajoules per square meter per day, growth and carbohydrate level increased with CO(2) enrichment under the control temperature regime but not under fluctuating temperatures. Plants in all growth regimens grew faster than in January.Over all plantings and growth regimens, relative growth rates were more highly correlated to total nonstructural carbohydrate levels than they were to irradiance, CO(2), or temperature.