Interplay between initial carbohydrate availability, current photosynthesis, and adventitious root formation in Pelargonium cuttings

Pelargonium was used to explore the interrelation between initial carbohydrate reserves and current photosynthesis in adventitious root formation (ARF) of leafy stem cuttings. The effects of pre-severance light intensity, short-term storage, and current light intensity were studied. Initial carbohydrate levels in the basal stems (BS) were positively correlated with pre-severance photosynthetic photon flux density (PPFD) and were only marginally reduced by storage. The storage-induced decrease in non-photochemical quenching (qN) of chlorophyll fluorescence (CF) and carbohydrate levels in leaves was compensated during the early rooting period. Concurrently, qN values, sugar levels in leaves, and sugar accumulation in the BS were lower for the high-light-adapted cuttings that received low light compared with their counterparts that were exposed to higher light or with low-light-adapted cuttings receiving the same light. The number of roots was positively correlated with initial concentrations of leaf sugars, especially sucrose, but only with a current PPFD ≤ 100 μmol m−2 s−1. When the PPFD was higher, the root number was dependent on the mean qN, which reflected the short-term adaptation of the photosynthetic apparatus to current PPFD. The entire variation in ARF was explained by the mean leaf sucrose concentrations of days 0 + 7, which reflected the stability of early leaf carbohydrate export. It is suggested that the leaf-derived influx of sugars or other co-transported molecules determines the intensity of ARF in leafy stem cuttings.