Carbon assimilation of petunia cuttings in a non-disturbed rooting environment: Response to environmental key factors and adventitious root formation

Abstract

Considering that adventitious root formation (ARF) relies on adequate supply of carbon, the objectives of this study were (I) to evaluate how CO2 assimilation contributes to the carbon balance of petunia cuttings and (II) to study the extent to which CO2 assimilation depends on the progress of ARF and environmental key factors. CO2 gas exchange and dry matter production of Petunia hybrida ‘Mitchell’ cuttings were monitored in a specifically designed multiple open chamber system using plastic covered rooting trays as measuring cuvettes connected to an infrared CO2 sensor. Excised cuttings were rooted for two weeks in a growth chamber at 22/20°C (day/night) at a photosynthetic photon flux density (PPFD) of 100μmolm−2s−1 and a CO2 concentration of approximately 400ppm. An increase in dry matter of 186mg per cutting, or 158% of the initial dry matter, reflected high carbon assimilation. Whilst the shoot dry matter of cuttings increased substantially in the very first week root dry matter growth was not observed until day seven after planting. The short-term response of CO2 gas exchange to environmental conditions revealed that net photosynthesis (PN) enhanced with increasing PPFD, with a maximum PN of 7.8μmolm−2s−1. Temperature response curves exhibited only minor changes of PN; dark respiration (RD) increased considerably when the temperature was temporarily increased. Furthermore, cuttings responded to an increase in CO2 concentration from 300 to 1200ppm by almost doubling PN. When cuttings were rooted permanently under PPFDs of 150μmolm−2s−1 and 80μmolm−2s−1 (22/20°C day/night; CO2 concentration 400ppm) PN and RD of cuttings at the higher PPFD were constantly higher than under the lower PPFD. The CO2 gas exchange of both treatments was relatively constant during ARF. The light response curves of PN differed after one week of exposure to the two light intensities. Light adaptation was comparable to that of stock plants measured using a portable infrared gas analyser equipped with a leaf chamber.The data indicates that petunia cuttings rooted under conditions frequently applied in young plant production in Central Europe show significant carbon assimilation from the first day onwards. The data also reveals that CO2 gas exchange under such conditions is not affected by ARF, but is subject to prevailing environmental factors such as light intensity, temperature and CO2 concentration.