Date Published: January 25, 2019
Publisher: Public Library of Science
Author(s): Zhen Guo, Jichang Han, Juan Li, Yan Xu, Xiaoli Wang, Andrew C Singer.
Soil microorganisms play a pivotal role in carbon mineralization and their diversity is crucial to the function of soil ecosystems. However, the effects of long-term fertilization on microbial-mediated carbon mineralization are poorly understood. To identify the relative roles of microbes in carbon mineralization of yellow paddies, we investigated the long-term fertilization effects on soil properties and microbial communities and their relationships with carbon mineralization. The treatments included: no fertilization (CK), chemical fertilizer (NPK), organic fertilizer (M), and constant organic-inorganic fertilizer (MNPK). NPK treatment significantly increased soil water content (WC), while M and MNPK treatments significantly increased the content of soil organic carbon (SOC), total nitrogen (TN), soil microbial biomass carbon (SMBC), soil microbial biomass nitrogen (SMBN), and WC. Strong increases in CO2 emissions, potential mineralized carbon, and turnover rate constant were observed in both organic-fertilizer treatments (M and MNPK), relative to the CK treatment. These changes in soil properties can be attributed to the variation in microbial communities. NPK treatment had no significant effect. Different fertilization treatments changed soil microbial community; SOC and SMBN were the most important contributors to the variance in microbial community composition. The variations in community composition did not significant influence carbon mineralization; however, carbon mineralization was significantly influenced by the abundance of several non-dominant bacteria. The results suggest that SOC, SMBN, and non-dominant bacteria (Gemmatimonadetes and Latescibacteria), have a close relationship to carbon mineralization, and should be preferentially considered in predicting carbon mineralization under long-term fertilization.
Soil is the largest carbon pool in terrestrial ecosystems, and about 1.5 × 1015 kg of carbon is present in the form of soil organic matter. The carbon in soil organic matter is about three times the carbon storage of terrestrial vegetation , and a large proportion of the total CO2 emissions in the world comes from decomposition of soil organic matter . The International Panel on Climate change (IPCC)  reported that agriculture is an important terrestrial ecosystem with the potential to mitigate the greenhouse effect. The natural potential of global agricultural greenhouse gas emission reduction is as high as 2300–6400 Mt CO2 equivalent per year, and more than 90% comes from reducing soil CO2 release. In the last 100 years, the increase in greenhouse gas concentrations caused by irrational farming practices and the massive burning of fossil fuels has changed the dynamic balance of carbon in the atmosphere [3–4]. The global surface temperature is expected to rise by 1.8–4.0 °C by the end of this century. Therefore, the study of soil organic carbon mineralization and its influencing factors has become one of the hot issues in global climate change.
Fig 1 shows the cumulative mineralized carbon under different fertilization treatments during the culture period. In this study, chemical fertilizer did not significantly affect SOC content. This is consistent with the study by Li et al. in which the effects of chemical and organic fertilizer on soil properties after wheat crops were studied . Li found no changes in carbon mineralization after chemical fertilization. In contrast, the application of organic fertilizer treatment in this study resulted in significantly increased carbon loss, as previously reported in other studies . Fangueiro showed that addition of livestock slurry to soil resulted in large increases in CO2 emissions . In our study, the total amounts of CO2 released after 30 d of incubation was significantly higher after organic fertilizer treatments (M and MNPK) compared to the chemical treatment. This data supports our hypothesis that organic fertilizer treatment can significantly increase organic carbon mineralization. The differences in organic versus chemical fertilizer effects may be due to inconsistent carbon inputs. Although the input of organic fertilizer directly increases the soil organic carbon content, organic fertilizers promote the growth of plants. The soil of chemical fertilizer application relies solely on the root residues and exudates of the crop to increase carbon input . Therefore, the carbon source in the soil treated by organic fertilizer treatment was more abundant, which enhanced the microbial activity and accelerated the carbon pool mineralization process. It is worth noting that in the organic fertilizer treatment, carbon emission, and potential mineralized carbon content of MNPK treatment were higher than the M treatment, but the difference between treatments was not significant. This result highlights the promotion of carbon mineralization by high nitrogen fertilizer (the sum of N fertilizer that is applied in M treatment and NPK treatment) in the MNPK treatment compared to the M treatment, consistent with the study by Henrique et al. .
Long-term fertilization influenced soil properties, microbial community, and C mineralization, and the differences were most obvious with constant organic-inorganic fertilizer treatment. Constant organic-inorganic fertilizer treatment significantly altered basic soil properties and increased organic C accumulation mineralization, potential mineralized C content, and turnover rate constant. We conclude that the difference in abundance of several bacteria influenced C mineralization, not the composition of soil microbial communities. In addition, SOC and SMBN were the most important contributors to the variance in microbial community composition. The non-dominant bacteria Gemmatimonadetes and Latescibacteria were significantly negatively correlated and positively correlated with C mineralization, which determined the difference in C mineralization.