Effects of CO2 Enrichment on the Responses of Legume-Rhizobia Symbiosis to Elevated Soil Temperature
Both planetary temperature and atmospheric carbon dioxide concentration are expected to increase in the coming decades, and to have significant effects on the growth of development of plants. Pisum sativum is an important food crop species that forms a mutualistic symbiosis with Rhizobia bacteria, which is likely to be affected by CO2 levels and soil temperature. Previous studies have found that elevated soil temperature increases root respiration and inhibits nodule development, and elevated CO2 levels increase short-term plant growth, nodule functioning and nodule abundance, although responses vary among species. Thus, we conducted a factorial experiment to study the effects of elevated CO2 and soil temperature on the responses of the Pisum sativum-Rhizobia symbiosis. Our results indicate that (1) CO2 enrichment increases legume growth and bacterial nitrogen fixation; (2) elevated soil temperature decreases legume biomass; and (3) the interaction of both factors is likely to inhibit the mutualism in the short term, opposing the positive effects of CO2 enrichment as a single factor. These findings suggest that future climate change may not benefit yield of Pisum sativum.
Keywords: elevated CO2, soil temperature, legume-rhizobia symbiosis, total biomass, carbon allocation, C:N ratio