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:It is clear from these results and those from previous studies Bagwell et al. 1998; 2001; Bergholz et al. 2001 that numerous diazotrophs inhabiting the rhizoplanes of salt marsh plants are strongly influenced by specific properties of the plant host and somewhat less influenced by the abiotic…
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