Metabolic nitrogen and carbohydrate pools as potential quality indicators of supply chains for ornamental young plants

Abstract The plasticity and physiological functions of metabolic nitrogen (N) and carbohydrate pools in the tissues of axillary shoot tip cuttings are poorly understood despite their pivotal role in pre-harvest growth, post-harvest abiotic stress resilience, survival and adventitious root (AR) formation in young plant supply chains for ornamental crops. Therefore, we studied the N and carbohydrate pools in response to contrasting experimental environments by both the graduated N supply of stock plants and the different dark storage amounts of the cuttings as well as during multi-seasonal transport of commercial cuttings from low-latitude stock plant facilities. The initial survey of cuttings from the supply chains confirmed species-specific optimal total nitrogen (N t ) levels and indicated further species differences both in N t allocation to metabolic N pools and in the total carbon (C t )/N t ratio in Chrysanthemum (CHRY), Euphorbia (POI), Impatiens (IMP), Osteospermum (OSTEO) and Pelargonium (PEL). For CHRY and PEL, frequency distributions of the N t content revealed that a significant percentage of commercial cuttings is not optimally supplied. The PEL cuttings responded to experimental dark storage with a gradual increase in mobile organic N pools at the expense of the proportion of N t of the matrix protein pool, which corresponded to reduced survival and rooting capacity, whereas the N t and nitrate levels remained unchanged. Analyses of commercial cuttings confirmed regular incidents of shifts in N t allocation from insoluble protein-N to mobile N pools; these shifts coincided with severe carbohydrate depletions during transport. Therefore, compared with leaf tissues, stem tissues displayed a higher resilience against carbohydrate depletion. In conclusion, monitoring deviation ranges and changes among N pools in addition to carbohydrates and N t is suggested. This monitoring is appropriate not only during growth before harvest but also throughout postharvest and helps to identify risks of low survival rate and low rooting before cuttings are planted. As a first parameter, a set of indicators for decision support is suggested. In this regard, the potential of near-infrared spectroscopy (NIRS) is discussed as rapid diagnostic tool that can easily be applied at critical points of the supply chains.