Microbial carbon source utilization in rice rhizosphere and non-rhizosphere soils in a 34-year fertilized paddy field.

Carbon (C) is playing an important role in regulating soil nutrient cycling, maintaining soil fertility and crop yield, but there is still need to further study on how C source utilization characteristic respond to soil physical and chemical properties change with different fertilizer treatments under a double-cropping rice (Oryza sativa L.) field in southern China. Therefore, the effects of 34-year long-term fertilizer regime on C source utilization characteristic in rice rhizosphere and non-rhizosphere soils under a double-cropping rice field in southern China were studied by using 18 O-H2 O method in the present paper. The field experiments were included four fertilizer treatments: mineral fertilizer alone (MF), rice straw and mineral fertilizer (RF), 30% organic manure and 70% mineral fertilizer (OM), and without fertilizer input as control (CK). The results showed that microbial biomass C content, basal respiration of soil microorganism and microbial growth rate in rice rhizosphere and non-rhizosphere soils with OM and RF treatments were significantly higher (p < .05) than that of CK treatment. The microbial C utilization efficiency (CUE) in rhizosphere soil with MF and CK treatments were significantly higher (p < .05) than that of OM treatment, but there was no significantly difference (p > .05) in microbial CUE in non-rhizosphere soil between MF, RF, OM, and CK treatments. In the different parts of soil, the microbial biomass C content and basal respiration of soil microorganism in rhizosphere soil were higher than that of non-rhizosphere soil, but the microbial growth rate and microbial CUE in non-rhizosphere soil were higher than that of rhizosphere soil. Compared with CK and MF treatments, the metabolic capacity of soil microorganism to exogenic C source with RF and OM treatments were significantly higher (p < .05) than that of MF and CK treatments. The largest type of exogenic C source used by soil microorganism was carboxylic acids, followed by amino acid and carbohydrate, and complex compounds was the smallest. In the different parts of soil, the metabolic capacity of soil microorganism to the types of exogenic C source in non-rhizosphere soil was higher than that of rhizosphere soil. The redundancy analysis results indicated that there had obvious difference in utilization characteristic of soil microorganism to exogenic C source among different fertilizer treatments. In conclusion, this results indicated that characteristic of soil C source utilization were significantly changed under different long-term fertilizer condition.