Data from: Long-term agricultural management does not alter the evolution of a soybean-rhizobium mutualism

Leguminous crops, like soybeans, often rely on biologically fixed nitrogen
via their symbiosis with rhizobia rather than synthetic nitrogen inputs.
However, agricultural management practices may influence the effectiveness
of biological nitrogen fixation. While the ecological effects of
agricultural management on rhizobia have received some attention, the
evolutionary effects have been neglected in comparison. Resource mutualism
theory predicts that evolutionary effects are likely, however. Both
fertilization and tillage are predicted to cause the evolution of rhizobia
that provide fewer growth benefits to plant hosts and fix less nitrogen.
This study capitalized on an LTER (Long Term Ecological Research)
experiment that manipulated agricultural management practices in a
corn-soybean-wheat row crop system for 24 years to investigate whether
four different management practices (conventional, no-till, low chemical
input, and certified organic) cause rhizobia populations to evolve to
become more or less cooperative. We found little evidence that 24 years of
varying management practices affect the net growth benefits rhizobia
provide to soybeans, although soybean plants inoculated with soils
collected from conventional treatments tended to have lower biological
nitrogen fixation rates than plants inoculated with soils from the
no-till, low input, and organic management treatments. These findings
suggest that rhizobia will continue to provide adequate growth benefits to
leguminous crops in the future, even in intensively managed systems.