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:The most common carboxylates in root exudates (citrate, malate, malonate, acetate, fumarate, succinate, lactate and oxalate) are primarily involved in respiration, stomatal regulation and other metabolic pathways (Rengel and Marschner 2005).
Category: