Effects of CO2 Enrichment on the Responses of Legume-Rhizobia Symbiosis to Elevated Soil Temperature

Abstract

Abstract

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