Effect of the combined application of fungal residue and chemical fertilizers on the mineralization of soil organic carbon in paddy fields

Fertilization makes strong associations between organic carbon composition and microbial properties in paddy soil

Fertilization changes the soil organic carbon (SOC) composition, affecting the carbon cycle of paddy soil. Understanding the mechanisms of physical fraction and chemical composition of SOC responding to fertilization can help regulate the nutrient release and carbon sequestration. However, it is unclear whether these changes in SOC composition to fertilization are consistent and how these are regulated by biotic and abiotic properties. Therefore, a positioning experiment in a rice field was conducted with a total of nine treatments. Chemical fertilizers (0, 337.5, and 675 kg ha^-1; C₀, C₅₀, and C₁₀₀, respectively) and fungal residue (0, 10,000, and 20,000 kg ha^-1; F₀, F₅₀, and F₁₀₀, respectively) were applied to evaluated (i) changes in the physical fraction and chemical composition of SOC, (ii) changes in soil properties, microbial biomass and community, and (iii) establish relationships among soil properties, microbial community, microbial biomass, and SOC composition. Our results showed that the application of fungal residue exhibited more significant effects on SOC physical fractions than those with the chemical fertilizers. Furthermore, the chemical composition of SOC was more respond to the application of chemical fertilizers than fungal residue. The partial least squares path model indicated that soil properties mainly affected the mineral-associated organic carbon (MAOC) by microbial biomass. In addition, bacterial diversity played an important role in improving the accumulation of MAOC. The SOC chemical composition was mediated by fungal community composition and bacterial diversity. In conclusion, fungal residue application affected SOC physical fraction by increasing soil properties, microbial biomass, and bacterial diversity. Chemical fertilizers application mainly mediated the chemical composition of SOC by altering fungal community composition and decreasing bacterial diversity.

Effects of white-rot fungal pretreatment of corn straw return on greenhouse gas emissions from the North China Plain soil

Straw-return with fungal treatment is a potential method for reducing soil greenhouse gas emissions through carbon (C) sequestration and N₂O mitigation. However, there is little information on the effects of different fungal treatments of crop straw return on soil CO₂ and N₂O emissions. To explore to what extent decomposed corn straw and its components controls soil CO₂ and N₂O emissions, we set up three sequential incubation experiments using soil collected from the North China Plain, an intensive agricultural area. Interactions between the different C contents of corn straw (CS), CS pretreated with Irpex lacteus (ICS), CS pretreated with Phanerochaete chrysosporium (PCS) and different NO₃^--N concentrations on the effect of soil CO₂ and N₂O emissions were conducted, and the kinetics of CO₂ and N₂O as influenced by changes in soil biochemical factors were analyzed. The effects of different lignocellulose components (lignin, cellulose, and xylan) on soil CO₂ and N₂O emissions were further studied. The results showed that straw pretreatment did not affect CO₂ emissions. Both CO₂ and N₂O emissions increased when the C and N contents increased. However, applying PCS to 70% water-filled pore space soil effectively decreased the soil N₂O emissions, by 41.8%-76.3% compared with adding the same level of CS. Moreover, extracellular enzyme activities related to C and N cycling were triggered, and the nosZI and nosZII abundances were significantly stimulated by the PCS application. These effects are closely related to the initial soluble C content of this treatment. Furthermore, adding xylan can significantly reduce N₂O emissions. Overall, our data suggest that the environmentally beneficial effects of returning straw can be greatly enhanced by applying the straw-degrading white-rot fungi of P. chrysosporium in the North China Plain soil. Future studies are needed in the field to upscale this technology.

The relationship between bacterial diversity and organic carbon mineralization in soft rock and sand compound soil

The soil organic carbon (SOC) mineralization rate in sandy soil plays an important role in improving soil quality, and a research is needed to determine management practices that optimize the mineralization rate. When sandy soil is improved by adding soft rock, the specific promotion process of bacterium to SOC mineralization remain unclear. To investigate these mechanisms, we selected four treatments with soft rock to sand volume ratios of 0:1 (CK), 1:5 (C1), 1:2 (C2) and 1:1 (C3) to study. The mineralization rate of organic carbon was measured using the lye absorption method. High-throughput sequencing and scanning electron microscopy were used to determine the bacterial community structure and soil microstructure, respectively. The results showed that the organic carbon content of the sandy soil increased significantly (182.22-276.43%) after using the soft rock treatments. The SOC mineralization rate could be divided into two stages: a rapid decline during days 1-8 and a slow decline during days 8-60. With increased incubation time, the intensity of the cumulative release of organic carbon gradually weakened. Compared with the CK treatment, the SOC mineralization accumulation (Ct) and the potential mineralizable organic carbon content (C₀) in the C1, C2, and C3 treatments increased significantly, by 106.98-225.94% and 112.22-254.08%, respectively. The cumulative mineralization rate (Cr) was 18.11% and 21.38% smaller with treatments C2 and C3, respectively. The SOC mineralization rate constant (k) decreased significantly after the addition of soft rock, while the half-turnover period (Th) changed inversely with k. Compared with the CK treatment, the number of gene copies of the soil bacteria increased by 15.38-272.53% after adding soft rock, with the most significant increase in treatment C3. The bacterial diversity index also increased significantly under treatment C3. The three dominant bacteria were Proteobacteria, Actinobacteria, and Chloroflexi. The correlation between C_r and one of the non-dominant bacteria, Firmicutes, was large, and the bacteria had a significant positive correlation with k. At the same time, the abundance of Firmicutes under treatments C2 and C3 was small. As the proportion of soft rock increased, the soil particles changed from point contact to surface contact, and the adhesion on the surface of the particles gradually increased. Results from this study show that the retention time of SOC can be increased and the carbon sequestration effect is better when the ratio of soft rock to sand is set to 1:2.

Response of organic carbon mineralization and bacterial communities to soft rock additions in sandy soils

Bacteria play a vital role in biotransformation of soil organic carbon (SOC). However, mechanisms of bacterium and organic carbon mineralization remain unclear during improvement of sandy soil using soft rock additions. In this study, four treatments with differing ratios of soft rock to sand of 0:1 (CK), 1:5 (C1), 1:2 (C2) and 1:1 (C3) were selected for mineralization incubation and high-throughput sequencing. The results showed that SOC, total nitrogen (TN), available phosphorus (AP), nitrate nitrogen (NO\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}${}_{3}^{-}$\end{document}3−-N), and mass water content (WC) of sandy soil increased significantly after addition of soft rock (P < 0.05). Compared with the CK treatment, cumulative mineralization and potential mineralized organic carbon content of C1, C2 and C3 increased by 71.79%–183.86% and 71.08%–173.33%. The cumulative mineralization rates of organic carbon treated with C1 and C2 were lower, 16.96% and 17.78%, respectively (P > 0.05). The three dominant bacteria were Actinobacteria, Proteobacteria and Chloroflexi, among which Proteobacteria was negatively correlated with mineralization of organic carbon (P < 0.01). The mineralization rate constant (k) was positively correlated and negatively correlated with Cyanobacteria and Nitrospirae, respectively. Under C2 treatment, Proteobacteria and Nitrospirae had the largest increase, and Cyanobacteria had the largest decrease. Compared with other treatments, C2 treatment significantly increased bacterial diversity index, richness index and evenness index, and the richness index had a negative correlation with k value. In conclusion, when the ratio of soft rock to sand was 1:2, the k of SOC could be reduced. In addition, the retention time of SOC can be increased, and resulting carbon fixation was improved.