Sanctions and mutualism stability: why do rhizobia fix nitrogen?
View/ Open
Date
2002Author
West, Stuart A
Kiers, E Toby
Simms, Ellen L
Denison, R Ford
Metadata
Abstract
Why do rhizobia expend resources on fixing N2 for the benefit of their host plant, when they could use
those resources for their own reproduction? We present a series of theoretical models which counter the
hypotheses that N2 fixation is favoured because it (i) increases the exudation of useful resources to related
rhizobia in the nearby soil, or (ii) increases plant growth and therefore the resources available for rhizobia
growth. Instead, we suggest that appreciable levels of N2 fixation are only favoured when plants preferentially
supply more resources to (or are less likely to senesce) nodules that are fixing more N2 (termed
plant sanctions). The implications for different agricultural practices and mutualism stability in general
are discussed.