Effect of Maize Straw Biochar on Bacterial Communities in Agricultural Soil

Enhanced immobilization of cadmium and lead in contaminated soil using calcium alginate-modified HAP biochar: Improvements in soil health and microbial diversity

A novel adsorbent, calcium alginate-modified HAP (Hydroxyapatite)-wood ear mushroom sticks biochar (CA-HAPMB), was synthesized to enhance the immobilization of Cd and Pb in soil. Over 150 days, applying CA-HAPMB at concentrations of 0%-3% in contaminated soils from Chenzhou City in Hunan Province (CZ) and Shenyang City in Liaoning Province (SY) resulted in decreased effective concentrations of Cd and Pb. Specifically, in CZ soil, Cd and Pb decreased by 30.9%-69.3% and 31.9%-78.6%, respectively, while in SY soil, they decreased by 27.5%-53.7% and 26.4%-62.3%, respectively. Characterization results, obtained after separating CA-HAPMB from the soil, indicate that complexation, co-precipitation, and ion exchange play crucial roles in the efficient immobilization of Cd and Pb by CA-HAPMB. Additionally, adjusting the amount of CA-HAPMB added allows modulation of soil pH, leading to increased soil organic matter and nutrient content. Following treatment with CA-HAPMB for immobilizing Cd and Pb, soil bacteria abundance and diversity increased, further promoting heavy-metal immobilization.

Optimistic contributions of plant growth-promoting bacteria for sustainable agriculture and climate stress alleviation

Global climate change is the major cause of abiotic and biotic stresses that have adverse effects on agricultural productivity to an irreversible level, thus threatening to limit gains in production and imperil sustainable agriculture. These climate change-induced abiotic stresses, especially saline, drought, extreme temperature, and so on affect plant morphological, physiological, biochemical, and metabolic characteristics through various pathways and mechanisms, ultimately hindering plant growth, development, and productivity. However, overuse and other inappropriate uses of agrochemicals are not conducive to the protection of natural resources and the environment, thus hampering sustainable agricultural development. With the vigorous development of modern agriculture, the application of plant growth-promoting bacteria (PGPB) can better ensure sustainable agriculture, due to their ability to improve soil properties and confer stress tolerance in plants. This review deciphered the underlying mechanisms of PGPB involved in enhancing plant stress tolerance and performance under various abiotic and biotic stresses. Moreover, the recent advancements in PGPB inoculation techniques, the commercialization of PGPB-based technology and the current applications of PGPB in sustainable agriculture were extensively discussed. Finally, an outlook on the future directions of microbe-aided agriculture was pointed out. Providing insights into plant-PGPB interactions under biotic and abiotic stresses and offering evidence and strategies for PGPB better commercialization and implementation can inspire the development of innovative solutions exploiting PGPB under climatological conditions.

Cow bone-derived biochar enhances microbial biomass and alters bacterial community composition and diversity in a smelter contaminated soil

Bone waste could be utilized as a potential amendment for remediation of smelter-contaminated soils. Nevertheless, the influences of cow bone-derived biochar (CB) on soil microbial biomass and microbial community composition in multi-metal contaminated mining soils are still not clearly documented. Hence, the cow bone was used as feedstock material for biochar preparation and pyrolyzed at two temperatures such as 500 °C (CB500) and 800 °C (CB800), and added to a smelter soil at the dosage of 0 (unamended control), 2.5, 5, and 10% (w/w); then, the soil treatments were cultivated by maize. The CB effect on soil biochemical attributes and response of soil microbial biomass, bacterial communities, and diversity indices were examined after harvesting maize. Addition of CB enhanced total nutrient contents (i.e., total nitrogen up to 26% and total phosphorus P up to 27%) and the nutrients availability (i.e., NH₄ up to 50%; NO₃ up to 31%; Olsen P up to 48%; extractable K up to 18%; dissolved organic carbon up to 74%) in the treated soil, as compared to the control. The CB500 application revealed higher microbial biomass C (up to 66%), P (up to 41%), and bacterial gene abundance (up to 76%) than the control. However, comparatively a lower microbial biomass nitrogen and diversity indices were observed in the biochar (both with CB500 and CB800) treated soils than in the unamended soils. At the phylum level, the highest dose (10% of CB500 and CB800 resulted in contrasting effects on the Proteobacteria diversity. The CB500₁₀ favored the Pseudomonas abundance (up to 793%), Saccharibacteria (583%), Parcubacteria (138%), Actinobacteria (65%), and Firmicutes (48%) microbial communities, while CB800₁₀ favored the Saccharibacteria (386%), Proteobacteria (12%) and Acidobacteria (11%), as compared to the control. These results imply that CB500 and CB800 have a remarkable impact on microbial biomass and bacterial diversity in smelter contaminated soils. Particularly, CB500 was found to be suitable for enhancing microbial biomass, bacterial growth of specific phylum, and diversity, which can be useful for bioremediation of mining soils.

Effect of pyrolysis temperature of biochar on Cd, Pb and As bioavailability and bacterial community composition in contaminated paddy soil

To further investigate the effect of pyrolysis temperature on bioavailable Cd, Pb and As, as well as the bacterial community structure in multi-metal(loid) contaminated paddy soil, six types of biochar derived from wood sawdust and peanut shell at 300 °C, 500 °C and 700 °C were prepared and incubated with Cd, Pb and As contaminated paddy soil for 45 days. The results showed that adding biochar decreased bioavailable Cd by 31.3%- 42.9%, Pb by 0.61-56.1%, while bioavailable As changed from 9.68 mg kg^-1 to 9.55-10.84 mg kg^-1. We found that pyrolysis temperature of biochar had no significant effect on Cd bioavailability while Pb bioavailability decreased obviously with pyrolysis temperature raising. Biochar reduced the proportion of soluble and exchangeable Cd from 45.0% to 11.2-15.4% in comparison with the control, while no significant effect on the speciation of Pb and As. Wood sawdust biochar (WSBs) had more potential in decreasing bioavailable Cd and Pb than peanut shell biochar (PSBs). Although high-temperature biochar resulted a larger increase in bacterial species than low-and mid- temperature biochar, feedstock played a more important role in altering soil bacterial diversity and community composition than pyrolysis temperature. PSBs increased the diversity of soil bacteria through elevating soil dissolved carbon (DOC). Biochar altered soil bacterial community structure mainly by altering the level of soil electricity conductivity, DOC and bioavailable Cd. In addition, applying high-temperature PSBs increased the genus of bacteria that relevant to nitrogen cycling, such as Nitrospira, Nitrosotaleaceae and Candidatus_Nitrosotalea.

Effect of nanohydroxyapatite/biochar/sodium humate composite on phosphorus availability and microbial community in sandy soils

Phosphorus (P) is essential for crop growth as an indispensable nutrient; however, there has been growing concern over the low use efficiency of P used in current fertilizers. We synthesized and characterized a potential P fertilizer nanohydroxyapatite/biochar/sodium humate (nHAP/BC/HANa) composite. To study the impact of the composite on soil chemical properties and microbial community in sandy soils, we set up four treatments as follows: (1) biochar (BC), (2) nanohydroxyapatite (nHAP), (3) nHAP/BC/HANa composite, and (4) sodium humate (HANa) was added separately into soils amended with nHAP/BC (nHAP/BC + HANa) to compare its performance with that of the nHAP/BC/HANa composite. A key finding was that the nHAP/BC/HANa composite not only significantly increased the soil available P content and alkaline phosphatase activity but also the increased organic matter content compared to the control. Additionally, leaching losses of P in soils amended with the nHAP/BC/HANa composite were lower than those in soils amended with the nHAP/BC + HANa, which suggested that the nHAP/BC/HANa composite had great potential to decrease P loss in sandy soils. Moreover, bacterial communities were more sensitive than fungal communities to all treatments. The bacterial communities showed the most significant changes in the nHAP/BC/HANa treatments. Results from Mantel tests further indicated that the strongest correlation between bacterial communities and soil properties occurring in the nHAP/BC/HANa treatments. Random forest analysis was conducted to identify the dominant microbial taxa, such as Proteobacteria, Acidobacteria, and Gemmatimonadetes, for predicting changes in soil properties. There was an asymptotical transition in bacterial community assembly processes from stochastic to deterministic in the nHAP/BC/HANa treatments. In conclusion, we demonstrated that nHAP/BC/HANa composite had the remarkable contribution to soil P availability in sandy soils, and simultaneously promoted the bacterial functions potential for P cycling, which present valuable insights to the development of potential P fertilizer.

Agricultural Waste-Based Biochar for Agronomic Applications

Agricultural activities face several challenges due to the intensive increase in population growth and environmental issues. It has been established that biochar can be assigned a useful role in agriculture. Its agronomic application has therefore received increasing attention recently. The literature shows different applications, e.g., biochar serves as a soil ameliorant to optimize soil structure and composition, and it increases the availability of nutrients and the water retention capacity in the soil. If the biochar is buried in the soil, it decomposes very slowly and thus serves as a long-term store of carbon. Limiting the availability of pesticides and heavy metals increases soil health. Biochar addition also affects soil microbiology and enzyme activity and contributes to the improvement of plant growth and crop production. Biochar can be used as a compost additive and animal feed and simultaneously provides a contribution to minimizing greenhouse gas emissions. Several parameters, including biochar origin, pyrolysis temperature, soil type when biochar is used as soil amendment, and application rate, control biochar’s efficiency in different agricultural applications. Thus, special care should be given when using a specific biochar for a specific application to prevent any negative effects on the agricultural environment.

Comparing straw, compost, and biochar regarding their suitability as agricultural soil amendments to affect soil structure, nutrient leaching, microbial communities, and the fate of pesticides

The emission of nutrients and pesticides from agricultural soils endangers natural habitats. Here, we review to which extent carbon-rich organic amendments help to retain nutrients and pesticides in agricultural soils and to reduce the contamination of surrounding areas and groundwater. We compare straw, compost, and biochar to see whether biochar outperforms the other two more traditional and cheaper materials. We present a list of criteria to evaluate the suitability of organic materials to be used as soil amendments and discuss differences in elemental compositions of straw, compost, and biochar to understand, how soil microorganisms utilize those materials. We review their effects on physical and chemical soil characteristics, soil microbial communities, as well as effects on the transformation and retention of nutrients and pesticides in detail. It becomes clear that for all three amendments their effects can vary greatly depending on numerous aspects, such as the type of soil, application rate, and production procedure of the organic material. Biochar is most effective in increasing the sorption capacity of soils but does not outperform straw and compost with regards to the other aspects investigated. Nevertheless, the possibility to design biochar properties makes it a very promising material. Finally, we provide critical comments about how to make studies about organic amendments more comparable (comprehensive provision of material properties), how to improve concepts of future work (meta-analysis, long-term field studies, use of deep-insight microbial DNA sequencing), and what needs to be further investigated (the link between structural and functional microbial parameters, the impact of biochar on pesticide efficiency).