Effect of interactions between carbon dioxide enrichment and NH/NO ratio on pH of culturing nutrient solution, growth and vigor of tomato root system

Abstract

A growth chamber experiment was conducted to investigate the influence of NH₄⁺/NO₃^- ratio and elevated CO₂ concentration on the pH in nutrient solution, growth and root vigor system of tomato seedling roots, which attempts to understand whether the elevated CO₂ concentration can alleviate the harmful effects of higher NH₄⁺–N concentration in nutrient solutions on the tomato root system. Tomato (Lycopersicon esculentum Mill. var. Hezuo 906) was grown in pots with nutrient solutions varying in NH₄⁺/NO₃^- ratio (0:1, 1:3, 1:1, 3:1 and 1:0) and the growth chambers were supplied with ambient (360 ?L·L^-1) or elevated CO₂ concentration (720 ?L·L^-1). The results showed that the pH changed with the growth process and CO₂ concentration increased. At both CO₂ levels, pH increased when 100% NO₃^-–N was supplied and decreased in other treatments. The pH decrease in the nutrient solution was directly correlated to the NH₄⁺-N proportion. The pH value was more reduced in 100% NH₄⁺–N nutrient solution than increased in the 100% NO₃^-–N nutrient solution. CO₂ enrichment increased the dry weight of shoots and roots, root vigor system, total absorbing area and active absorbing area of tomato seedlings. All the measurement indexes above were increased in the elevated CO₂ concentration treatment with the NO₃^- proportion increase in the nutrient solutions. Thus, under the elevated CO₂ concentration, the dry weights of shoots and roots, root vigor system, total root absorbing area and active absorbing area were found to be inversely correlated to NH₄⁺/NO₃^- ratio, leading to about 65.8%, 78.0%, 18.9%, 12.9% and 18.9% increase, respectively, compared with that under the ambient CO₂ concentration. Our results indicated that tomato seedling roots may benefit mostly from CO₂ enrichment when 100% NO₃^-–N nutrient solutions was supplied, but the CO₂ concentration elevation did not alleviate the harmful effects when 100% NH₄⁺–N was supplied.

Keywords

tomato / pH / roots / growth and development