The use of grafting techniques for horticultural crops increases plant tolerance to various abiotic and biotic stresses. Tomato production under greenhouse conditions relies on plants grafted onto vigorous rootstocks because they sustain crops for longer periods. Growers under Mediterranean conditions usually grow crops in passive greenhouses during the summer and winter season, to provide fresh products throughout the year. No information is available with regard to the effect of the environment on nitrogen-use efficiency (NUE) in tomato plants grafted onto rootstocks with different vigor. In the present study, NUE, along with its components—uptake (NUpE) and utilization (NUtE) efficiencies—were evaluated in tomato plants grafted onto two interspecific rootstocks, conferring medium (“King Kong”) or high (“Kaiser”) vigor to the plants. The evaluations were carried out during the vegetative and reproductive stage in plants subjected to different environmental conditions resulting in different plant growth rates. The grafting treatments did not affect NUE, NUpE or NUtE in young plants, but at the reproductive stage, differences were found during the summer season (high N demand) where the vigorous rootstock increased NUpE from 55%, in non-grafted plants, to 94%, with the consequent differences in NUE. During the winter crop, no differences in NUE were found between the vigorous rootstock and non-grafted plants, but the less vigorous (cold-tolerant) rootstock enhanced NUpE. Significant positive relationships were found between plant growth rate and both NUE and NUpE, while NUtE decreased with increasing growth rate.
Rootstock x Environment Interactions on Nitrogen-Use Efficiency in Grafted Tomato Plants at Different Phenological Stages
