The Effect Of Elevated CO₂ Concentration On Yield-associated Physiology And Microbial Molecular Ecology In The Rhizosphere Of Soybean

Atmospheric CO₂ concentration increases during global climate change. The concentration of CO₂ has increased from 270 ?mol·l-1 pior to the Industrious Revolution to 390 ?mol·l-1 in2013. It is expected to reach 700 ?mol·l-1 by the end of this century. The increase of CO₂ concentration may impact soybean production. However, the studies on effect of elevated CO₂?eCO₂? on physiological and biochemical characteristics and microbial molecular ecology in the rhizosphere are rare. Such investigations will be essential to improve soybean adaptability to elevated CO₂ environments in theory.Using open top chamber, we investigated 24 soybean cultivars in response to eCO₂ with respects to photosynthetic rate, chlorophyll content, hormone activity, Rubp enzyme activity, N accumulation and yield. Total DNA in the rhizosphere was extracted and sequenced with Illumina sequencer. We investigated the 16S-rDNA gene diversity in the rhizosphere in response to eCO₂. The various physiological responses between cultivars under eCO₂ were compared.Thus, the association of physiological response with microbial molecular ecology was assessed.The results were presented as followed. The photosynthetic rate at the flowing stage increased by 23.1% to 99.2% under eCO₂. At the seed-filling stage, however, photosynthetic rate was not affected by eCO₂ as much as at the flowering stage. Leaf chlorophyll content had a similar trend with photosynthetic rate. It increased by 12.5%⁷2.2% under eCO₂. The IAA concentration in leaf and Rubp activity were not affected by eCO₂. Regarding N uptake, leaf N concentration did not change under e CO₂ compared to ambient CO₂, and there was no difference between cultivars. However, the leaf N content increased significantly under eCO₂. As the photosynthetic characteristics had significant responses to eCO₂, the substantial changes in the transportation of photosynthetic C to underground and root exudates occur. This is likely to affect the interaction between microbes and crop plants. In term of rhizospheric ecology, PCoA?principal coordinate analysis? result showed that eCO₂ changed the soil microbial communities.Analysis of the genera abundance?read numbers? with a two-way ANOVA showed that the genera of Gaiellales_uncultured, Acidimicrobiaceae_uncultured, Arthrobacter, Catelliglo bosispora, Bryobacter, Bradyrhizobium, Ensifer, Pedomicrobium, Xanthomonadales_uncultured,Roseiflexus, Flavisolibacter, Chitinophagaceae_uncultured, 480-2_norank, Gitt-GS-136_norankand 288-2_norank in the rhizosphere were significantly affected by CO₂, and the CO₂-induced responses of genera of Pseudomonas, Escherichia-Shigella and RB41_norank were dependent on cultivars. There were 8 genera, i.e.Acidimicrobiales_uncultured, Iamia, Blastococcus, Nitrosomonadaceae_uncultured,Escherichia-Shigella, Bacillus, 480-2_norank, GR-WP33-30_norank being significantly mediated by soybean cultivars. The seed yield increased under eCO₂ compared to ambient CO₂, but the yield response depended on cultivar. There was93.2% of increase in Mufeng 5 while no significant change in Suinong 14 and Dongsheng 8. Yield had a significant correlation with photosynthetic rate and between yield and leaf chlorophyll content.Elevated CO₂ significantly stimulated physiological characteristics of soybean and the extent of this stimulation varied between cultivars, which determined the yield gain CO₂ under such condition. The photosynthetic C distribution in response to eCO₂ contributed to the change of microbial community composition. This study revealed,for the first time, the abundance of microorganisms on the genus level being affected by eCO₂ in the soybean-planted Mollisol, which may be associated with soil nutrient cycling and plant productivity.