Short-day pre-treatment coordinates adventitious rooting and flowering in cannabis cuttings

The effects of short-day pre-treatment (SDP; 12/12 h) on adventitious root formation (ARF) and flowering transition in medicinal cannabis ( Cannabis sativa L.) cuttings were investigated. It was hypothesized that SDP induces a physiological priming state that promotes ARF by creating a developmental transition zone in which reduced gibberellin (GA) activity coincides with maintained endogenous auxin levels. Mother plants were exposed to 0, 1, or 2 weeks of SDP, after which cuttings were harvested and rooted under short-day rooting (SDR) conditions. The 1-week SDP/SDR treatment exhibited the earliest ARF and produced the highest number of adventitious roots. This treatment also initiated flowering 7 days after transplanting (DAT), substantially shortening the overall cultivation cycle compared with the control and the 0-week SDP/SDR treatment. Chlorophyll a fluorescence kinetics (JIP-test) revealed that the 1-week SDP/SDR enhanced phenomenological energy absorption ( ABS / CS m ) and trapping ( TR ₀/ CS m ), maintaining sufficient physiological activity to support ARF. In contrast, although the 2-week SDP/SDR showed the highest reduction capacity at the PSI terminal acceptor ( RE ₀/ CS m = 13,077), ARF was completely suppressed. This response was associated with excessive electron influx, acceleration of the Mehler reaction, and a sharp increase in H 2 O 2 accumulation (240 μmol·g −1 dry weight (DW)), indicating severe oxidative stress. Overall, a 1-week SDP/SDR regime represents an optimal cultivation strategy for synchronizing ARF and flowering in cannabis without exogenous hormone application, by balancing energy flux regulation and oxidative stress control. • One-week short-day pre-treatment (SDP)/short-day rooting (SDR) maximizes adventitious rooting in medicinal cannabis. • SDP/SDR synchronizes rooting and flowering in cuttings. • Flowering occurs just 7 days post-transplant in pre-treated cuttings. • One-week SDP/SDR activates the full photosynthetic electron transport chain without oxidative stress. • SDP/SDR shortens cultivation time, improving vertical farm efficiency.