Wenfu Chen

Biochar as a novel niche for culturing microbial communities in composting

Biochar has been applied as a bulk agent or an additive to compost. The mixture of biochar and compost has been considered to exert synergistic effect as a soil amendment. In a composting system, the macro-porous sites of biochar may act as a novel niche that selects and cultures the microorganisms from the bulk compost. A variety of volatile organic carbons (VOCs) such as aromatic hydrocarbons and aliphatics were detected in biochar pellets (BC) pyrolyzed at 100°C. In the mesosphilic phase, the water-soluble carbon (WSC) and water-soluble phenols (WSP) in biochar increased from 2.1 to 26mgkg(-1) and 5.9 to 101μgkg(-1), respectively. These labile carbons however, were subjected to a rapid metabolism over the composting course. We further compared the responses of microbial community in BC to those in the bulk organic matter. Both Shannon-Wiener and Richness indexes of bacterial communities were higher in BC than in the adjacent compost (ADJ) and the bulk organic matter (control). As for fungal communities, the two indexes were higher in BC than ADJ and control only in the mature phase. During the composting course, the bacterial activity was higher than the fungal counterpart in terms of the changes of corresponding biomarkers, glucosamine and muramic acids. The results suggested that the diversified labile carbons sources including VOCs and WSC in BC could influence the structure of microbial community and resulted in an enhanced carbon catabolic capacity.

Effect of volatile organic compounds absorbed to fresh biochar on survival of Bacillus mucilaginosus and structure of soil microbial communities

PurposeBiochar is considered difficult for microorganisms to decompose, and volatile organic compounds (VOCs) sorbed to fresh biochar may affect the survival rate of inoculants or the structure of soil microbial communities. We tested the hypotheses that VOCs on fresh biochar may play a vital role in shaping the structure of soil microbial communities and determined if they inhibited or supported the growth of inoculants.Materials and methodsWe examined the growth of Bacillus mucilaginosus in mushroom medium-based biochar (MM-biochar), corn stalk-based biochar (CS-biochar), and rice straw-based biochar (RS-biochar) in comparison with peat. The composition of VOCs before and after the incubation was characterized by pyrolysis-gas chromatography/mass spectroscopy (GC-MS). The structure of a soil microbial community incubated in biochar was examined via denaturing gradient gel electrophoresis (DGGE). Canonical correspondence analysis (CCA) was applied to reveal the contribution of pH, K and Na, and diversity indices from VOC fingerprints to diversity indices in DGGE profiles.Results and discussionIn the present study, all biochars were able to support B. mucilaginosus at population densities analogous to peat. Phenols comprise a fraction of the VOCs that potentially could be toxic to some microbes and inhibit their growth in the short time. The structure of the inoculated soil microbial communities in terms of the diversity indices calculated from 16S ribosomal DNA (16S rDNA) and 18S rDNA DGGE profiles was greatly affected by biochar. Besides, CCA revealed the role of VOCs in shaping the structure of soil microbial communities.ConclusionsVOCs absorbed to biochar, despite their short life spans, could support the survival of B. mucilaginosus, demonstrating the potential of biochars as carriers for inoculants. The changes in the soil microbial communities induced by fresh biochar may not represent the long-term “biochar effect.” Therefore, future work needs to appreciate mechanisms underlying aged biochar on the structure of soil microbial communities.

Effects of abiotic components induced by biochar on microbial communities

Soil microorganisms play an important role on ecosystems and are influenced by a variety of abiotic and biotic variables. The influence of biochar on the microbial community has been reported, but its mechanism modifying soil microbial distribution is less understood. In this paper, biochar was physically separated from soil, and the abiotic characteristics generally recognised influencing soil microbial communities were examined. The microbial community structure was assessed via denaturing gradient gel electrophoresis (DGGE). The influence of abiotic components including available N, Olsen P and extractable K, pH and C/N induced by biochar on soil microbial communities was compared by canonical correspondence analysis (CCA). Results indicated that biochar fostered more fungi and stimulated bacteria growth in the adjacent soil. Biochar particles at three sampling times exhibited the similar microbial community composition, although it was also impacted by temporal factors. Phylogenetic distributions of the operational taxonomic units (OTUs) could be divided into the following eight groups: Bacillaceae, Gemmatinomadetes, Sphingomanas, Acidobacteria, Proteobacteria, Chloroflexaceae, Actibacteria (similarity > 95%) and unknown (similarity < 85%). CCA revealed the great contribution of C/N, Olsen P and extractable K to fungi growth, and C/N and Olsen P to actinomycete abundance. The presence of biochar not only induced increase of available nutrients but also increased microbial biomass and diversity, which indicated beneficial effects on soil microorganisms and soil fertility.

Effects of biochar application on nitrogen leaching, ammonia volatilization and nitrogen use efficiency in two distinct soils

This study was conducted to determine the effect of biochar application on nitrogen (N) leaching, ammonia (NH3) volatilization, and fertilizer N use efficiency (NUE) in two soils with different properties (loamy and sandy). Ryegrass (Lolium perenne L.) incubation experiments (with 15N-enriched urea applied) and an N loss simulation study were conducted at biochar application rates of 2% and 4%. The results showed that 15N utilization increased by 8.83–9.06% following the addition of biochar to sandy soil during the first season compared with the control. However, this significant effect was not observed in the loamy soil, in which significantly more urea-N was retained in the soil following biochar application. Furthermore, based on the results of the N leaching and NH3 volatilization experiments, 29.19% and 28.65% NO3-N leaching reductions were induced by 2% and 4% biochar amendments in loamy soil, decreasing the total inorganic N that was leached (NH4+-N plus NO3-N) by 26.46% and 26.82%, respectively. However, although the amount of leached NH4+-N decreased in biochar-amended sandy soil, the cumulative NH3 volatilizations were 14.18–20.05% higher than in the control, and 22.55% more NO3--N was leached from biochar-amended sandy soil, resulting in a negative effect on N retention. According to this study, biochar can be effectively used to improve the NUE in sandy soil and reduce N loss from loamy soil.

Organic Molecules from Biochar Leacheates Have a Positive Effect on Rice Seedling Cold Tolerance

Biochar is known to have a number of positive effects on plant ecophysiology. However, limited research has been carried out to date on the effects and mechanisms of biochar on plant ecophysiology under abiotic stresses, especially responses to cold. In this study, we report on a series of experiments on rice seedlings treated with different concentrations of biochar leacheates (between 0 and 10% by weight) under cold stress (10°C). Quantitative real-time PCR (qRT-PCR) and cold-resistant physiological indicator analysis at low temperatures revealed that the cold tolerance of rice seedlings increased after treatment with high concentrations of biochar leacheates (between 3 and 10% by weight). Results also show that the organic molecules in biochar leacheates enhance the cold resistance of plants when other interference factors are excluded. We suggest that the positive influence of biochar on plant cold tolerance is because of surface organic molecules which likely function by entering a plant and interacting with stress-related proteins. Thus, to verify these mechanisms, this study used gas chromatography-mass spectrometry (GC-MS) techniques, identifying 20 organic molecules in biochar extracts using the National Institute of Standards and Technology (NIST) library. Further, to illustrate how these organic molecules work, we utilized the molecular docking software Autodock to show that the organic molecule 6-(Methylthio)hexa-1,5-dien-3-ol from biochar extracts can dock with the stress-related protein zinc-dependent activator protein (ZAP1). 6-(Methylthio)hexa-1,5-dien-3-ol has a similar binding mode with the ligand succinic acid of ZAP1. It can be inferred that the organic molecule identified in this study performs the same function as the ZAP1 ligand, stimulating ZAP1 driving cold-resistant functions, and enhancing plant cold tolerance. We conclude that biochar treatment enhances cold tolerance in rice seedlings via interactions between organic molecules and stress related proteins.

Maize stover biochar increases urea ( 15 N isotope) retention in soils but does not promote its acquisition by plants during a 4-year pot experiment

Biochar as a soil amendment has been shown to improve soil quality and crop growth. However, biochar’s effect on urea-N use efficiency in long term is not well elucidated. Here we studied urea-N (15N isotope) allocation in plants and soil in the presence of maize (Zea mays L.) stover biochar (equivalent to 46 t ha-1) during a 4-yr pot trial. Results showed that biochar only increased maize biomass (about 9%) with high amount of urea addition, which indicates the increased maize dry weight by biochar application could be attributed to synergistic effects between biochar and urea. Soil total N contents and fertilizer N retention were increased by 20% and 10.47% to 94.52%, respectively, indicating that biochar was more capable for fertilizer N retention than promote plant adsorption. Moreover, inorganic N content in biochar treatment was greatly increased, which implies the increased N mineralization. In total, we concluded that biochar application was a potential urea enhancer during plant production.

Can biochar provide ammonium and nitrate to poor soils?: Soil column incubation

Understanding how nitrogen concentrations respond to biochar amendment in different types of soils is important for agricultural management. Here, we analyzed the effects of amendment with rice hull biochar on sandy soil, red soil, and alkaline soil (coastal solonchak) over 13 months, focusing on factors such as ammonium (NH4 +-N) and nitrate (NO3 −-N) cumulative leachate losses, pH, cumulative volumes of leachates, NH4 +-N and NO3 −-N abundance of soils, soil dehydrogenase, and nitrogen-related soil enzyme activities. Our results indicated that biochar amendment increased the pH of red soil but decreased the pH of both sandy and coastal solonchak soils; promoted the retention of NH4 +-N in red and sandy soils, but not in coastal solonchak; and reduced the loss of NO3 −-N during the early stages of leaching but accelerated losses during subsequent leaching stages. Soil nitrogen supply capacity (NH4 +-N + NO3 −-N) greatly increased over the short term, with significant differences between treatments. Further, biochar enhanced concentrations of NH4 +-N and NO3 −-N in soils, and the addition of biochar stimulated the enzymatic and microbial activities in soil, which may increase the abundance of NH4 +-N and NO3 −-N. Finally, we found that the response of NH4 +-N and NO3 −-N to biochar addition varied among the different soil types.