Regulation of the C:N Ratio Improves the N-Fixing Bacteria Activity, Root Growth, and Nodule Formation of Peanut

This study is to investigate the effect of different C:N ratios on the soil-microorganism-plant system in peanut ( Arachis hypogaea L. ). A pot experiment was conducted to determine how different ratios of exogenous carbon (glucose) to nitrogen (urea) (C:N0 with 0.9 g N/pot, C:N5 with 0.9 g N/pot, 11.25 g glucose/pot, C:N15 with 0.9 g N/pot, 33.75 g glucose/pot, C:N25 with 0.9 g N/pot, 56.25 g glucose/pot) could influence peanut growth and soil microbial communities. Results showed that averaged plant height, lateral branch length, plant biomass, and the chlorophyll content (SPAD) were respectively significantly increased by 26.02%, 32.38%, 21.74%, and 7.07%, compared with C:N0 treatment. C addition treatments significantly improved total root length, total surface area, and total root volume. The δ 13 C values in whole plants and roots increased with the increasing of C:N ratio, while the δ 15 N values firstly increased and then decreased, in comparison with C:N0 treatment. The C addition had a significant influence on soil bacterial diversity in the peanut root zone. In comparison with the C:N0, the abundance-based ACE and Chao index all obviously increased. Pearson correlation showed that nodule numbers, root surface area correlated positively with Rhodocyclales , Zoogloeaceae , and Myxococcales , Anaeromyxobacteraceae , respectively. Moreover, different C:N ratios changed the soil bacterial community. The bacterial communities in the C addition treatments had higher species richness than those in the no C addition treatments. The results indicate that C addition ameliorates soil nutrient conditions and provides the benefits to soil bacterial communities and root and plant growth .