Human activities have altered the global nitrogen (N) cycle, and as a result, elevated N inputs are causing profound ecological changes in diverse ecosystems. The evolutionary consequences of this global change have been largely ignored even though elevated N inputs are predicted to cause mutualism breakdown and the evolution of decreased cooperation between resource mutualists. Using a long-term (22 year) N addition experiment, we find that elevated N inputs have altered the legume-rhizobium mutualism (where rhizobial bacteria trade N in exchange for photosynthates from legumes), causing the evolution of less mutualistic rhizobia. Plants inoculated with rhizobium strains isolated from N-fertilized treatments produced 17–30% less biomass and had reduced chlorophyll content compared to plants inoculated with strains from unfertilized control plots. Because the legume-rhizobium mutualism is the major contributor of naturally-fixed N to terrestrial ecosystems, the evolution of less cooperative rhizobia may have important environmental consequences.
Weese et al Dryad data
This excel file has two tabs: one of the tabs has the data for the soil inoculation experiment (“experiment 1, see manuscript), the other tab has the data for the genetic effects experiment (“experiment 2, see manuscript). Below are descriptions of the variables in this data file. More information is in the manuscript.
plantid: randomly assigned plant ID number.
shootmass: dry above ground mass of individual experimental plant (units is grams).
leafnum: number of leafs counted on an individual experimental plant
stolonnum: number of stolons counted on an individual experimental plant
nodulenum: number of nodules counted on an individual experimental plant
MassofNodules: mass of 1st 100 nodules (approximately, see “Nodulesintube” variable) taken from an individual experimental plant. Units is grams.
NodulesinTube: the number of nodules that were weighted in for the “MassofNodules” variable
meannodulemass: estimated average mass of a nodule sampled from an individual experimental plant, calculated by dividing the “MassofNodules” variable by the “NodulesinTube” variable
totalnodulemass: estimated total mass of all nodules for an individual experimental plant, calculated by multiplying “meannodulemass” variable by “nodulenum” variable
Chlor: measured chlorophyll level for an individual experimental plant (no units)
Harvester: initials of individual that harvested an individual experimental plant.
Harvestdate: date that an individual exerperimental plant was harvested.
Harvestday: number of days that had past since the 1st experimental plant was harvested.
strain: identity of rhizobia strain that inoculated that particular experimental plant
nitrogen: describes whether the particular rhizobia strain inoculating this experimental plant was originally sampled from a fertilized field plot (1) or a nonfertilized field plot (0)
field: LTER T7 experimental field from which the particular rhizobia strain inoculating this experimental plant was originally sampled from
plot: label associated with a particular plot within a particular LTER T7 field coded thusly: 1A = the nonfertilized subplot of LTER field 1, 1B = the fertilized subplot of LTER field 1, 2A = the nonfertilized subplot of LTER field 2, 2B = the fertilized subplot of LTER field 2, and so on…
plantspori: Trifolium species from which a particular rhizobia strain was isolated during the soil inoculation experiment
plantpopori: particular population (associated with a Trifolium species) from which a particular rhizobia strain was isolated during the soil inoculation experiment
plantssprear: Trifolium species of that particular experiment plant
plantpoprear: population (associated with a Trifolium species) of that particular experimental plant.
