Non-nitrogen Benefits and Costs of Rhizobia to Plants
Rhizobia are soil-dwelling bacteria capable of forming symbiotic relationships with legume plants, where legume root systems form “nodules” for rhizobia to reside. Rhizobia are nitrogen-fixing, thus providing the host plant with nitrogen and receiving carbon in return. Some strains of rhizobia may additionally produce plant hormones or modify hormone signaling by their host plant. Is this an additional benefit of rhizobia or a cost that reduces net benefits to plants? We hypothesized that, in the case of wild type rhizobial strains producing plant hormones such as gibberellin, benefits may outweigh costs depending on environmental factors. Understanding the relationship between plant yield and hormone-producing rhizobia may contribute insight to the maximization of agricultural yields. We grew MN0095 soybean plants inoculated with a wild type gibberellin-producing strain, USDA 110, and a knockout version, GA(-), to determine their effect on plant growth and plant yield. To do this, we measured water usage (proxy for leaf area), harvested plant biomass, and harvested seed weight. Measured nitrogen fixation can also be used to understand how deviations in seed yield might result from the contributions of hormone-producing strains. Our experiment found significant data of host plants with gibberellin-producing strains requiring more water (g/day). We also found trends of higher harvested host plant and seed yield dry weight with gibberellin-producing strains than host plants without, indicating possible benefits of hormone-producing strains.