Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:during B deficiency has been considered harmful for the plant growth through their enhanced oxidation (Cakmak and Römheld 1997) and the B-deficiency induced production of excess phenolic acids has even been proposed to cause eventual death of plants (Lee and Aronoff 1967).
Category: