Pretreatment and Enzymatic Hydrolysis of Sorghum Bran

Sorghum bran has potential to serve as a low‐cost feedstock for production of fuel ethanol. Sorghum bran from a decortication process (10%) was used for this study. The approximate chemical composition of sorghum bran was 30% starch, 18% hemicellulose, 11% cellulose, 11% protein, 10% crude fat, and 3% ash. The objective of this research was to evaluate the effectiveness of selected pretreatment methods such as hot water, starch degradation, dilute acid hydrolysis, and combination of those methods on enzymatic hydrolysis of sorghum bran. Methods for pretreatment and enzymatic hydrolysis of sorghum bran involved hot water treatment (10% solid, w/v) at 130°C for 20 min, acid hydrolysis (H₂SO₄), starch degradation, and enzymatic hydrolysis (60 hr, 50°C, 0.9%, v/v) with commercial cellulase and hemicellulose enzymes. Total sugar yield by using enzymatic hydrolysis alone was 9%, obtained from 60 hr of enzyme hydrolysis. Hot water treatment facilitated and increased access of the enzymes to hemicellulose and cellulose, improving total sugar yield up to 34%. Using a combination of starch degradation, optimum hot water treatment, and optimum enzymatic hydrolysis resulted in maximum total sugar yield of up to 75%.     

Contents of Indigestible Fraction,Water Solubility,and Color of Pyrodextrins Made from Waxy Sorghum Starch

To investigate the effect of prethinning of starch by acid before pyrolysis on the formation of indigestible fraction (IF) in pyrodextrins, native and prethinned (50°C for 1, 4, and 24 hr) waxy sorghum starches were heated at 120–160°C with 20–60 μL of 9% HCl/g of starch. Pyrodextrin containing 14.6% IF, measured as total dietary fiber by enzymatic‐gravimetric method, was produced at 120°C with 20 μL of HCl from native waxy sorghum starch. Prethinning before pyrolysis increased IF content by 0–68%, depending on the conditions for pyrolysis, compared with that of the native starch. Reduction in the molecular size of starch by prethinning might cause greater mobility during pyroconversion reaction and thus generate higher IF contents. Increasing temperature and acid concentration during pyroconversion also increased IF content of pyrodextrins. Pyrodextrin of 44.9% IF was produced at 160°C with 60 μL of HCl from prethinned starch (50°C for 24 hr). Solubility of pyrodextrins was inversely proportional to IF content (r = ‐0.87) and had a range of 62.7–98.3%. Color of pyrodextrins became brownish with more severe pyroconversion conditions.     

Enhanced Degradation of Atrazine by Soil Microbial Fuel Cells and Analysis of Bacterial Community Structure

Atrazine degradation in soil microbial fuel cells (MFCs) under different anode depths and initial concentrations is investigated for different redox soil conditions, and the microbial communities in the anode and different layers are evaluated. Atrazine degradation is fastest in the upper layer (aerobiotic), followed by the lower layer (anaerobic). A removal efficiency and a half-life of 91.69% and 40 days, respectively, are reported for an anode depth of 4 cm. The degradation rate is found to be dependent on current generation in the soil MFCs rather than on electrode spacing. Furthermore, the degradation rate is inhibited when the initial atrazine concentration is increased from 100 to 750 mg/kg. Meanwhile, the exoelectrogenic bacteria, Deltaproteobacteria and Geobacter, are enriched on the anode and the lower layer in the soil MFCs, while atrazine-degrading Pseudomonas is only observed in very low proportions. In particular, the relative abundances of Deltaproteobacteria and Geobacter are higher for lower initial atrazine concentrations. These results demonstrate that the mechanism of atrazine degradation in soil MFCs is dependent on bioelectrochemistry rather than on microbial degradation.     

Biotreatment of Melanoidin-Containing Distillery Spent Wash Effluent by Free and Immobilized Aspergillus oryzae MTCC 7691

Humic acids (HA) are known as the precursors of carcinogenic compounds formed by the disinfection of drinking water. While conventional treatments were found to be inefficient HA removal processes in drinking water, advanced oxidation processes have been proven to have a significant effect in the treatment of HA. The degradation of HA was investigated using nano-sized zinc oxide (ZnO)/laponite composite (NZLC). The reactions occurred in a UVC reactor by considering following variables: pH, initial HA concentration, catalyst loading, addition of hydrogen peroxide (H₂O₂), and catalyst reuse. Water samples containing HA were analysed by ultraviolet/visible spectrophotometer and high-performance size-exclusion chromatography. Initial HA concentrations were tested by the Langmuir–Hinshelwood model with k and K _ads values, determined to be 0.126 mg/L.min and 0.0257 L/mg, respectively. The change in pH affected the HA degradation efficiency by the photocatalytic activity where it was higher under acidic conditions rather than alkaline ones. Optimal catalyst loading was proved to be a constrained factor in influencing the photocatalytic efficiency: the increase of catalyst concentration enhanced the HA decomposition efficiency up to an optimum value of 20 g/L, where there was no further degradation with excess loading. The addition of H₂O₂ was investigated through homogenous and heterogeneous photocatalysis, and, heterogeneous photocatalysis showed higher removal efficiency due to the combined effect of both catalysts and H₂O₂. Finally, NZLC was effective for reuse and exhibited an excellent stability after six times of usage.     

Degradation of Polycyclic Aromatic Hydrocarbons (PAHs) in Waste Wood

PAH-contaminated waste wood is a serious environmental problem. As an alternative to incineration and landfill disposal, wood containing PAHs may be detoxified by composting. The efficiency of this process depends on the composting conditions. The aerobic treatment of PAH-containing wood was therefore investigated under varying environmental conditions with particular attention to the kinetics of PAH degradation and wood mineralization. The composting of pine wood spiked with 2 g/kg phenanthrene, anthracene and pyrene each and subsequently artificially aged was studied on a laboratory-scale using a respiration analyzer. The temperature was found to highly influence both PAH degradation and wood decay. The fastest and most extensive PAH degradation and wood mineralization were found at 30°C. Higher temperatures particularly inhibited the degradation of anthracene and pyrene. The addition of urea markedly accelerated both PAH degradation and wood mineralization. Only small amounts of urea were needed to maximize PAH degradation, whereas higher amounts of urea were required to maximize wood mineralization. Urea hydrolyzes to ammonium carbonate, which in turn forms highly volatile ammonia. When more then 2 g/kg urea-N was added to the wood, excessive nitrogen disappeared as ammonia via the gas phase. Using nitrate instead of urea dramatically reduced both PAH degradation and wood mineralization. Although a slightly alkaline pH seemed to promote PAH degradation, it has to be taken into account that this experiment was carried out with nitrate as an N source rather than urea to avoid any N losses at high pH values. Glucose as a cosubstrate neither accelerated PAH degradation nor stimulated wood decay. Molasses as a cosubstrate actually inhibited PAH degradation since it contains much salt and alkalinized the rot material.     

Performance of Anaerobic Biotrickling Filter and Its Microbial Diversity for the Removal of Stripped Disinfection By-products

The objective of this research was to evaluate the biodegradation of chloroform by using biotrickling filter (BTF) and determining the dominant bacteria responsible for the degradation. The research was conducted in three phases under anaerobic condition, namely, in the presence of co-metabolite (phase I), in the presence of co-metabolite and surfactant (phase II), and in the presence of surfactant but no co-metabolite (phase III). The results showed that the presence of ethanol as a co-metabolite provided 49% removal efficiency. The equivalent elimination capacity (EC) was 0.13 g/(m³ h). The addition of Tomadol 25-7 as a surfactant in the nutrient solution increased the removal efficiency of chloroform to 64% with corresponding EC of 0.17 g/(m³ h). This research also investigated the overall microbial ecology of the BTF utilizing culture-independent gene sequencing alignment of the 16S rRNA allowing identification of isolated species. Taxonomical composition revealed the abundance of betaproteobacteria and deltaproteobacteria with species level of 97%. Azospira oryzae (formally dechlorosoma suillum), Azospira restrica, and Geobacter spp. together with other similar groups were the most valuable bacteria for the degradation of chloroform.     

两品种猕猴桃果实采后淀粉降解特性比较分析

为探究猕猴桃果实采后淀粉降解规律,本试验以红阳(HY)和翠玉(CY)猕猴桃果实为材料,比较分析了不同品种猕猴桃果实采后淀粉含量变化以及淀粉降解相关基因的表达模式。结果表明,猕猴桃采后25℃贮藏过程中,HY猕猴桃果实硬度迅速下降并伴随出现乙烯跃变,CY果实硬度缓慢下降但并未出现乙烯释放高峰。2个品种猕猴桃果实的淀粉含量随贮藏时间的延长显著下降。扫描电镜(SEM)结果显示,随着贮藏时间的延长,2个品种猕猴桃果实淀粉粒表面的光滑球面均出现不同程度的消化和破碎,说明淀粉存在酶促降解。同时,HY猕猴桃果实贮藏后期的乙烯释放速率极显著高于CY猕猴桃(P<0.001)。HY猕猴桃果实外果肉中淀粉含量在贮藏前期(0~2 d)极显著高于CY猕猴桃(P<0.01),但在贮藏后期(8~12 d)极显著低于CY猕猴桃(P<0.001);HY猕猴桃果实果心中淀粉含量在贮藏前期(2~4 d)与CY猕猴桃无显著差异,但在贮藏后期(6~12 d)极显著低于CY猕猴桃(P<0.001)。本研究结果为进一步揭示猕猴桃果实采后淀粉降解机理提供了一定的理论依据。     

Sonochemical Degradation of Chlorinated Phenolic Compounds in Water: Effects of Physicochemical Properties of the Compounds on Degradation

This study examined a comparative degradation of various chlorinated phenolic compounds including phenol, 4-chlorophenol (4-CP), 2,6-dichlorophenol (2,6-DCP), 2,4,6-trichlorophenol (2,4,6-TCP), 2,3,4,6-tetrachlorophenol (2,3,4,6-TeCP), and pentachlorophenol (PCP) using 28, 580, and 1,000 kHz ultrasonic reactors. The concentration of hydrogen peroxide was also determined in order to investigate the efficacy of different sonochemical reactors for hydroxyl radical production. Clearly, it was observed that the 580 kHz sonochemical reactor had maximum efficacy for hydroxyl radical production. The degradation of all the compounds followed the order; 580 kHz (91?C93%) > 1,000 kHz (84?C86%) > 28 kHz (17?C34%) with an initial concentration of 2.5 mg L^?1 at a reaction time of 40 min with ultrasonic power of 200 ± 3 W and aqueous temperature of 20 ± 1°C in each experiment. Overall, the degradation of those phenolic compounds followed the order, PCP > 2,3,4,6-TeCP > 2,4,6-TCP > 2,6-DCP > 4-CP > phenol at various frequencies in the presence/absence of a radical scavenger (tert-butyl alcohol). It was revealed that the correlations between the compound degradation rates and the physicochemical parameters, R ² = 0.99 for octanol?Cwater partition coefficient, R ² = 0.95 for water solubility, R ² = 0.94 for vapor pressure, and R ² = 0.88 for Henry??s law constant, excluding PCP, were very good in the entire range of each parameter.     

Starch degradation by alpha-amylase in tobacco leaves during the curing process

Tobacco (Nicotiana tabacum L.) leaf starch is degraded to sugars through curing (42°C/82.3% relative humidity/72 h). Total carbohydrate content remained almost constant, starch content decreased markedly, and soluble sugar content (mostly glucose) increased. α-Amylase and starch phosphorylase activities increased sixfold and threefold, respectively, whereas β-amylase activity was unaltered and isoamylase activity decreased. Increased α-amylase activity was accompanied by increased α-amylase protein levels. Although tobacco has four α-amylase gene members, only NtAMY1 mRNA levels increased. For other starch degradation genes, such as NtBAM1 and NtBMY2 (β-amylase), NtISO1 and NtISO2 (isoamylase) and NtGWD1 and NtGWD3 (glucan water dikinase), the mRNA levels remained unaltered during the first 48 h of curing. NtAMY1 expression was induced by osmotic stress but was unaffected by high temperature and/or injury stresses. Similarly, soluble sugar contents were largely increased by osmotic stress. This suggests that starch is degraded by α-amylase during curing and that α-amylase is coded by NtAMY1, induced by osmotic stress.     

Influence of mixtures of acenaphthylene and benzo[a]anthracene on their degradation by Pleurotus ostreatus in sandy soil

Purpose

Polycyclic aromatic hydrocarbons (PAHs) are a class of organic compounds commonly found as soil contaminants. Fungal degradation is considered as an environmentally friendly and cost-effective approach to remove PAHs from soil. Acenaphthylene (Ace) and Benzo[a]anthracene (BaA) are two PAHs that can coexist in soils; however, the influence of the presence of each other on their biodegradation has not been studied. The biodegradation of Ace and BaA, alone and in mixtures, by the white rot fungus Pleurotus ostreatus was studied in a sandy soil.

Materials and methods

Experimental microcosms containing soil spiked with different concentrations of Ace and BaA were inoculated with P. ostreatus. Initial (t ₀) and final (after 15 days of incubation) soil concentrations of Ace and BaA were determined after extraction of the PAHs.

Results and discussion

P. ostreatus was able to degrade 57.7% of the Ace in soil spiked at 30 mg kg^?1 dry soil and 65.8% of Ace in soil spiked at 60 mg kg^?1 dry soil. The degradation efficiency of BaA by P. ostreatus was 86.7 and 77.4% in soil spiked with Ace at 30 and 60 mg kg^?1 dry soil, respectively. After 15 days of incubation, there were no significant differences in Ace concentration between soil spiked with Ace and soil spiked with Ace + BaA, irrespective of the initial soil concentration of both PAHs. There were also no differences in BaA concentration between soil spiked with BaA and soil spiked with BaA + Ace.

Conclusions

The results indicate that the fungal degradation of Ace and BaA was not influenced by the presence of each other’s PAH in sandy soil. Bioremediation of soils contaminated with Ace and BaA using P. ostreatus is a promising approach to eliminate these PAHs from the environment.     

Screening of Microorganisms for Biodegradation of Simazine Pollution (Obsolete Pesticide Azotop 50 WP)

The capability of environmental microorganisms to biodegrade simazine—an active substance of 2-chloro-s-triazine herbicides (pesticide waste since 2007)—was assessed. An enormous metabolic potential of microorganisms impels to explore the possibilities of using them as an alternative way for thermal and chemical methods of utilization. First, the biotope rich in microorganisms resistant to simazine was examined. Only the higher dose of simazine (100 mg/l) had an actual influence on quantity of bacteria and environmental fungi incubated on substrate with simazine. Most simazine-resistant bacteria populated activated sludge and biohumus (vermicompost); the biggest strain of resistant fungi was found in floral soil and risosphere soil of maize. Compost and biohumus were the sources of microorganisms which biodegraded simazine, though either of them was the dominant considering the quantity of simazine-resistant microorganisms. In both cases of periodic culture (microorganisms from biohumus and compost), nearly 100% of simazine (50 mg/l) was degraded (within 8 days). After the repeated enrichment culture with simazine, the rate of its degradation highly accelerated, and just after 24 h, the significant decrease of simazine (20% in compost and 80% in biohumus) was noted. Although a dozen attempts of isolating various strains responsible for biodegradation of simazine from compost and biohumus were performed, only the strain identified as Arthrobacter urefaciens (NC) was obtained, and it biodegraded simazine with almost 100% efficiency (within 4 days).     

Effect of Roundup Ultra on atrazine degradation in soil

Tank mixing pesticides and the use of pre-packaged mixtures have become common agricultural practices. However, pesticide degradation in multi-pesticide systems is rarely evaluated. The objective of this laboratory study was to determine the effect of Roundup Ultra on atrazine degradation in soil. Based on a 2-mm glyphosate-soil interaction depth, the isopropylamine salt of glyphosate was added to Aatrex-amended and non-amended soil at rates of 0, 1 (43 mg ai kg ^-1), 2, 3, 4, and 5×. Treatments were incubated for 4, 8, 12, 16, 20, 24, 28, and 32 days. Atrazine degradation was significantly different among treatments at 8 days. In the 0× treatment (Aatrex only), 87% of the atrazine was degraded. During the same 8-day period, atrazine degradation in the 1, 2, 3, 4, and 5× treatments was 77%, 69%, 60%, 61%, and 52%, respectively. Atrazine degradation approached 97% for all treatments after 12 days and statistical differences were no longer observed. Atrazine degradation was inversely correlated with Roundup Ultra rate and microbial activity at 8 ( r ²=0.97) and 12 days ( r ²=0.92). These results indicate that Roundup Ultra stimulated microbial activity while simultaneously inhibiting atrazine degradation.     

Comparison of Enzymatic (E‐Mill) and Conventional Dry‐Grind Corn Processes Using a Granular Starch Hydrolyzing Enzyme

A new low temperature liquefaction and saccharification enzyme STARGEN 001 (Genencor International, Palo Alto, CA) with high granular starch hydrolyzing activity was used in enzymatic dry‐grind corn process to improve recovery of germ and pericarp fiber before fermentation. Enzymatic dry‐grind corn process was compared with conventional dry‐grind corn process using STARGEN 001 with same process parameters of dry solid content, pH, temperature, enzyme and yeast usage, and time. Sugar, ethanol, glycerol and organic acid profiles, fermentation rate, ethanol and coproducts yields were investigated. Final ethanol concentration of enzymatic dry‐grind corn process was 15.5 ± 0.2% (v/v), which was 9.2% higher than conventional process. Fermentation rate was also higher for enzymatic dry‐grind corn process. Ethanol yields of enzymatic and conventional dry‐grind corn processes were 0.395 ± 0.006 and 0.417 ± 0.002 L/kg (2.65 ± 0.04 and 2.80 ± 0.01 gal/bu), respectively. Three additional coproducts, germ 8.0 ± 0.4% (db), pericarp fiber 7.7 ± 0.4% (db), and endosperm fiber 5.2 ± 0.6% (db) were produced in addition to DDGS with enzymatic dry‐grind corn process. DDGS generated from enzymatic dry‐grind corn process was 66% less than conventional process.     

Bioremediation of Hexachlorocyclohexane-Contaminated Soil by the New <Emphasis Type="Italic">Rhodococcus wratislaviensis</Emphasis> Strain Ch628

Currently, there are large areas of soils contaminated with hexachlorocyclohexane (HCH) isomers which are included in the group of persistent organic pollutants. For the bioremediation of such soils, a new HCH-degrading Rhodococcus wratislaviensis strain Ch628 was isolated from long-term organochlorine contaminated soils. The strain Ch628 was able to degrade 32.3% γ-hexachlorocyclohexane (γ-HCH/lindane), 25.2% hexachlorobenzene, and 100% chlorobenzene in resting cell conditions. The strain Ch628 was bioaugmented in chronically HCH-contaminated soil. The results showed that the bioaugmentation of contaminated soil with the strain Ch628 led to HCH degradation. In the bioaugmented system, the efficiency of HCH removal at the initial concentration of about 238.7 ± 4.9 mg kg^?1 soil was 44.8%, while the system with indigenous microflora (without R. wratislaviensis strain Ch628) and the system with abiotic control removed 33.3 and 16.4% of this compound during the same period, respectively. Strain Ch628 could effectively degrade α-, β-, and γ-isomers of HCH (77.1, 100, and 100%, respectively) and heptachlorocyclohexane (69.9%) in the model soil systems. Moreover, the bioaugmentation with the strain Ch628 led to degradation of tri-, tetra-, and penta-chlorobenzenes, which are of HCH degradation metabolites. For the first time, it was found that the bioaugmentation with the bacterial strain Rhodococcus wratislaviensis Сh628 led to a significant reduction of the toxicity of the HCH-contaminated soil for the test organisms, such as Chlorella vulgaris Beijer and Daphnia magna Straus.     

Effect of carbofuran on enzymatic activities and growth of tomato plants in natural,fertilized and vermicompost-amended soils

The effects of carbofuran, a widely used carbamate pesticide, on soil enzymatic activities such as fluorescein diacetate hydrolysis (FDAH), dehydrogenase, and acid and alkaline phosphatases were studied at different time intervals in unamended soil and soil amended with inorganic fertilizers and vermicompost, cropped with tomato plants. The results showed that all enzymatic activities varied with carbofuran application rates and increased significantly up to 1.0 kg active ingredient (a.i.) ha^?1 dose of carbofuran. The most significant increase was observed at 0.20 kg a.i. ha^?1 dose both in unamended and amended soils. This showed that carbofuran was not toxic to all enzymatic activities studied upto 1.0 kg a.i. ha^?1 dose of carbofuran in both systems. A significant decrease in all enzymatic activites were observed at higher dose of carbofuran both in unamended and amended soils relative to their respective controls. Highest enzymatic activities were observed in vermicompost amended soil and minimum in fertilized soil compared to control. The results indicated that the growth of tomato plants was significantly higher at 0.20 kg a.i. ha^?1 dose of carbofuran in all the cases and followed the order: fertilized soil > vermicompost amended soil > natural soil and was positively correlated with the enzyme activities.     

Anaerobic Dechlorination of Tetrachlorobisphenol A in River Sediment and Associated Changes in Bacterial Communities

Tetrachlorobisphenol A (TCBPA) is a widely used flame retardant and a potential endocrine disruptor. We estimated the role of the microbial community in degradation of TCBPA in river sediment from the vicinity of an E-waste processing facility. The effects of different anaerobic conditions on degradation efficiency of TCBPA were investigated, and differences in bacterial communities among these conditions were analyzed by 16S ribosomal RNA (rRNA) gene sequencing. The most effective dechlorination of TCBPA occurred under methanogenic conditions followed by electron donor-enhanced conditions and sulfate-reducing conditions with initial sulfate concentrations of 1, 10, and 20 mM. The extent of TCBPA removal under these conditions mentioned above was 65, 44, 43, 23, and 23%, respectively. 16S rRNA gene sequence analysis indicated that five dominant genera in the phylum Chloroflexi and another five species of Bacteroidetes, Chlorobi, and Firmicutes in these five systems were largely involved in TCBPA dechlorination. The initial sample had a total relative abundance of autochtonous potential dechlorinating bacteria of 12%. After 160 days, these values increased to 29–43% under above conditions. Addition of TCBPA decreased bacterial diversity. Efficiency of TCBPA degradation depends on the abundance and metabolism of dechlorinating bacterial guilds. The effectiveness of dechlorinating microbes in degradation of TCBPA was reduced by high sulfate concentrations.     

Microbial response of soils with organic and conventional management history to the cultivation of Bacillus thuringiensis (Bt)-maize under climate chamber conditions

An experiment was carried out in a climate chamber to analyse if Bt-maize may cause particular changes in soils with different levels of microbial biomass and activity due to long-term management history. Among the soils selected, the ones managed organically for 30 years exhibited twice the microbial biomass and 2.6 times the dehydrogenase activity (DHA) of the soil from a field with long-term conventional maize monoculture. Soils were cultivated twice in a row with Bt-maize, its near-isogenic line and a conventional breeding line. We tested the hypotheses that (a) soil microbial biomass and activity are affected by the cultivation of Bt-maize and that (b) the influence of Bt-maize depends on the level of soil microbial biomass and activity. Shoot and root yield and shoot C-content of Bt-maize were higher than the ones of the near-isogenic line. DHA under Bt-maize was 6 % higher, and the metabolic quotient for CO₂ (qCO₂) was 9 % lower than under its near-isogenic line, giving some support to hypothesis (a). No significant interactions of the soils and the varieties used were found in this study, thus hypothesis (b) was not confirmed, and soils with different microbial biomass and activity appear to react in a similar way to the cultivation of Bt-maize.     

Fate of 15 N-labeled fertilizer in soils under dryland agriculture after 19 years of different fertilizations

This study addressed if long-term combined application of organic manure and inorganic fertilizers could improve the synchrony between nitrogen (N) supply and crop demand. ¹⁵?N-labeled urea was applied to micro-plots within three different fertilized treatments (no fertilizer, No-F soil; inorganic NPK fertilizers, NPK soil; and manure plus inorganic NPK fertilizers, MNPK soil) of a long-term field trial (1990–2009) in a dryland wheat field in the south Loess Plateau, China. After one season of wheat harvest, ¹⁵?N use efficiency was 20, 58, and 65 % in the No-F, NPK, and MNPK soil, respectively. During the early wheat growth stage, microbial immobilization of applied ¹⁵?N was significantly (P?<?0.05) highest in the MNPK soil (15.3 %), higher in the NPK soil (12.6 %), and lowest in the No-F soil (7.4 %). Of the ¹⁵?N immobilized by the soil microbial biomass, 69 % (NPK soil) to 83 % (MNPK soil) was released between the stem elongation and flowering of wheat. Compared with the NPK soil, the MNPK soil had significantly (P?<?0.05) higher grain yield. Our findings highlight that long-term application of organic manure with inorganic fertilizers cannot only improve the synchrony of N supply for crop demand but also increase N use efficiency and grain yield.     

Role of woody biochar and fungal-bacterial co-inoculation on enzyme activity and metal immobilization in serpentine soil

Purpose

In this study, we investigated the effect of biochar (BC) and fungal bacterial co-inoculation (FB) on soil enzymatic activity and immobilization of heavy metals in serpentine soil in Sri Lanka.

Materials and methods

A pot experiment was conducted with tomatoes (Lycopersicon esculentum L.) at 1, 2.5, and 5 % (w/w) BC ratios. Polyphenol oxidase, catalase and dehydrogenase activities were determined by idometric, potassium permanganate oxidisable, and spectrophotometric methods, respectively. Heavy metal concentrations were assessed by 0.01 M CaCl₂ and sequential extraction methods.

Results and discussion

An increase in BC application reduced polyphenol oxidase, dehydrogenase, and catalase activity. The application of FB increased soil dehydrogenase activity, with the maximum activity found in 1 % BC700?+?FB treatment. Moreover, the CaCl₂ extractable metals (Ni, Mn, and Cr) in 5 % BC700 amended soil decreased by 92, 94, and 100 %, respectively, compared to the control. Sequential extraction showed that the exchangeable concentrations of Ni, Mn, and Cr decreased by 55, 70, and 80 % in 5 % BC700, respectively.

Conclusions

Results suggest that the addition of BC to serpentine soil immobilizes heavy metals and decreases soil enzymatic activities. The addition of FB to serpentine soil improves plant growth by mitigating heavy metal toxicity and enhancing soil enzymatic activities.

     

Use of cyanobacterial polysaccharides to promote shrub performances in desert soils: a potential approach for the restoration of desertified areas

The importance of cyanobacterial polysaccharides of biological soil crusts in sand surface stabilization and soil nutrient retention has been long acknowledged. However, the role of cyanobacterial polysaccharides as a source of nutrition to vascular plants in crusted areas is ignored. In this study, the chemical composition of the polysaccharide synthesized by Phormidium tenue and the effects of its presence on seed germination and seedling metabolism of the shrub Caragana korshinskii were investigated. The crude polysaccharide synthesized by P. tenue was composed of 15 % protein and 58 % carbohydrate and showed the presence of 12 different types of monosaccharides. The addition of the polysaccharide significantly (P?<?0.05) increased seed germination and metabolic activity of the seedling of the shrub C. korshinskii. The optimal concentration for vigor index, root length, root vigor, and total N and P contents was 10 mg/L polysaccharide; for the germination rate, nitrate reductase activity, carbohydrate content, chlorophyll, and Mg²⁺ content, the optimal was 60 mg/L polysaccharide, while for K⁺ and Ca²⁺ contents, photosynthetic efficiency and superoxide dismutase activity was 120 mg/L. The presence of the polysaccharide increased seed germination rate, ion uptake, and photosynthetic activity by affecting the electron transport chain and decreased oxidative damage by eliminating reactive oxygen species in C. korshinskii, thus promoting shrub performance in crusted desert areas.