Survival and rooting capacity of ornamental cuttings as related to total nitrogen, storage condition and shift in metabolic N pools

In the course of vegetative propagation, cuttings of many ornamental species are subjected to critical dark storage particularly during their transport to distant rooting stations. Carbohydrate and nitrogen reserves in the cutting, as modulated by factors like N supply to stock plants and light conditions, greatly influence formation of adventitious roots (AR) and propagation success. To evaluate how storage affects the cutting quality, we assessed leaf senescence and survival, nitrogen allocation, as well as the rooting response of Chrysanthemum indicum and Pelargonium zonale cuttings. Cuttings of stock plants cultivated with graduated N fertigation (low/medium/high) were either planted immediately after harvest or first exposed to dark storage at high or low temperatures (15 vs. 5°C) for a short or extended period (3 d vs. 6/7 d). Stock plants and cuttings during rooting received an average daily light integral of ≥4 and ≥8 mol d^-1 m^‑2), respectively. In parallel to assessing the survival and AR formation, composition of the metabolic N pools (i.e., soluble amide N, nitrate N, amino N, insoluble protein N) was determined using a modified Kjeldahl analysis. The chlorophyll content of the second oldest leaf, calculated indirectly via SPAD readings, was chosen as an indicator for leaf senescence. A prolonged warm, dark exposure accelerated leaf senescence and decreased the survival during rooting in Pelargonium. However, cuttings surviving under those conditions showed a higher number and length of AR with both genera. This behaviour was stimulated at raised N supply and accompanied by a decrease in protein N content in favour of mobile N compounds, indicating a stronger N mobilization compared to absent or shorter and colder storage. Consequently, the applicability of different N compounds as early predictors for cutting performance after storage is discussed.