Effects of elevated root-zone CO2 on nutrient uptake and rhizosphere microbiome in Oriental Melon (Cucumis melo var. makuwa Makino).

Despite the significance of CO2 as a crucial gaseous component in the soil environment, the effects of increased root-zone CO2 concentrations on the physiological responses of melon and the corresponding rhizosphere microbiome are still not well understood. This study examined the effects of elevated root-zone CO2 on oriental melon (Cucumis melo var. makuwa Makino) ('Yu Mei Ren') in a pot experiment under controlled O2 conditions. Treatments included a control group (3000 μmol·mol-¹ CO2) and three elevated concentrations: T1 (6000 μmol·mol-¹), T2 (9000 μmol·mol-¹), T3 (12000 μmol·mol-¹). This study assessed plant growth, nutrient uptake, and rhizosphere soil properties, encompassing physicochemical characteristics and microbial community structure. The results indicated that at 10 days of treatment, T1, T2, and T3 significantly suppressed melon growth and nutrient assimilation. Additionally, a reduction in rhizosphere soil pH and an increase in electrical conductivity (EC) were noted. These differences became increasingly pronounced with extended treatment. Analysis of the rhizosphere microbial community indicated that elevated root-zone CO2 decreased both diversity and richness, while simultaneously increasing the relative abundance of the phyla Acidobacteria and Actinobacteria, along with genera such as SBR1031 and A4b. These results indicate that long-term elevated root-zone CO2 not only induces soil acidification and alters microbial community structure, but also impairs root nutrient acquisition.