Long-term Fertilization Enhances Soil Carbon Stability by Increase the Ratio of Passive Carbon: Evidence From Four Typical Croplands

Aims Soil organic carbon (SOC) plays an important role in improving soil quality, however how long-term fertilization influences SOC and contrasting active carbon (AC) and passive C (PC) pools at large scale remains unclear. The aim of this study was to examine the effect of long-term fertilization on SOC, including AC and PC, across four typical croplands in China and to explore the potential relationships and mechanism. Methods We assessed the effect of different fertilization (standard and 1.5 × standard of inorganic fertilizer (NPK) with or without manure (M), with a control for comparison) at soil depths (0-20 cm, 20-40 cm, 40-60 cm) on SOC, AC and PC. Results We found that SOC, AC and PC increased in the order Control < NPK < NPKM < 1.5NPKM. 1.5NPKM resulted in a significant increase in SOC, AC and PC, of 76.3%, 53.0% and 108.5% respectively across the soil profile (0-60 cm) compared with Control. The response ratio of PC to long-term fertilization was 2.1 times greater than that of AC across four sites on average. In addition, Clay was identified as the most important factor in explaining the response of AC and PC to different fertilization application, respectively. Conclusions Long-term fertilization enhanced both AC and PC, but the greater response of PC suggests that fertilization application could enhance the stability of carbon and thus the potential of cropland for soil carbon accumulation.

Rhizosphere Enzyme Activities and Microorganisms Drive the Transformation of Organic and Inorganic Carbon in Saline - Alkali Soil Region

Soil inorganic carbon (SIC) is the main existing form of soil carbon pool in arid saline-alkali land, and its quantity distribution affects the pattern of soil carbon accumulation and storage. Previous studies on soil carbon mostly focus on organic carbon (SOC), and pay little attention to SIC. The purpose of this study was to investigate the effect of microorganisms and soil enzymes on the transformation of SOC and SIC in the rhizosphere soil of three maize fields (M1, M2 and M3) and three paddy fields (R1, R2 and R3) under saline-alkali stress, which is a new research topic of soil carbon cycle in saline-alkali soil region. The results showed that the root - soil - microorganism interaction was changed by saline-alkali stress. The results of RDA analysis showed that Proteobacteria, Gemmatimonadetes, Planctomycetes, Nitrospirae, catalase, invertase, amylase and β-glucosidase had significant effects on the transformation of SOC and SIC (P<0.05). SOC and SIC in maize and rice rhizosphere soil were mainly driven by soil enzymes and microorganisms under saline-alkali stress, exchangeable sodium percentage (ESP) and pH were the main factors affecting the conversion process of SOC and SIC.