Burial Experiment Research Articles

A biodegradable ZnFe2O4/PLLA electrospun fibers based longitudinal mode piezoelectric membrane for health monitoring

Recently, multifunctional sensors based on piezoelectric active film fabricated with environmental friendly materials is a nascent field which can address the growing concern of electronic waste. Nevertheless, frequently utilized poly(vinylidene fluoride) (PVDF) and poly(L-lactic acid) (PLLA) encounter challenges of limited biocompatibility and weak piezoelectricity with low shear piezoelectric coefficient (d14), respectively. Accordingly, a biodegradable piezoelectric sensor comprising of PLLA nanofiber blended with ZnFe2O4 nanoparticles was developed in this work. The ZnFe2O4 nanoparticles served as heterogeneous nucleation center leading to improved piezoelectric coefficient and output than pure PLLA due to more consistent orientation of CO dipoles. The ZnFe2O4/PLLA film exhibited significant performance improvement featured with 1.7-fold higher longitudinal piezoelectric coefficient (d33 ∼ 6.5 ± 0.3 pm/V), nearly 250 % boosting on the output voltage. The ZnFe2O4/PLLA piezoelectric sensor induced high sensitivity (2–10 N:0.55 V/N; 10–32 N:0.29 V/N) and excellent mechanical stability for 27,000 cycles. The results of the soil burial experiment demonstrate that the film can degrade by over 75 % within 90 days, confirming its excellent biodegradability. Moreover, the ZnFe2O4/PLLA nanofibers based piezoelectric sensor could serve as effective detection evidenced by different output signals of head motion, pulse and artery beating demonstrating its feasible application for health monitoring. Considering the characteristics of straightforward fabrication and readily accessible sustainable materials, the ZnFe2O4/PLLA sensor provides an appealing eco-friendly solution for self-powered flexible personal devices disregarding the need to dispose of electronic waste.

Honeycomb porous regenerated cellulose aerogel films with enhanced thermal dissipation for agricultural mulch application

Agricultural films, essential to contemporary agricultural production, are mostly made from non-biodegradable petroleum-based materials. The use of such films, especially in high-temperature environments, contributes to elevated internal temperatures in direct sunlight, adversely affecting crop appearance and quality. In this work, rice straw was used as the raw material to prepare biodegradable chemically crosslinked regenerated cellulose aerogel films (RCAF-CC) by combining physical dissolution regeneration, chemical cross-linking, and freeze-drying. The resulting RCAF-CC is notable for its high middle-infrared emissivity and high solar reflectivity, which significantly aid in thermal dissipation for agricultural mulch by enhancing infrared radiation and solar reflection. Compared to traditional polyethylene films, RCAF-CC, with its superior radiative cooling properties and lower water vapor transport rate, has a significant advantage in the growth trend and survival rate of cherry radishes. It is worth noting that the RCAF-CC achieved the degradation rate of 74.4 % in the 100-day soil burial experiment, and the soybean seeds grown in the degraded soil grew well, showing excellent eco-friendliness. These results show that RCAF-CC can be an alternative source of traditional agricultural films, solving the problems of non-biodegradable and high internal temperatures of the films under direct sunlight.

Development of Biodegradable Bioplastics with Sericin and Gelatin from Silk Cocoons and Fish Waste.

The bioplastics sector promotes environmentally friendly means of cutting down on the usage of fossil fuels, plastic waste, and environmental pollution. Plastic contamination has detrimental effects on both ecological systems and the global food supply. The approach we present here to resolve this issue involves the integration of sericin and gelatin, obtained from cocoon and fish waste, respectively, with nano-reinforced cellulose crystals, to develop a biodegradable and compostable plastic material. The use of cocoon and fish wastes for the extraction of sericin and gelatin presents an environmentally beneficial approach since it contributes to waste reduction. The sericin level found in silk cocoon waste was determined to be 28.08%, and the gelatin amount in fish waste was measured to be 58.25%. The inclusion of sericin and gelatin in bioplastics was accompanied by the incorporation of glycerol, vinegar, starch, sodium hydroxide, and other coloring agents. Fourier transform infrared (FTIR) examination of bioplastics revealed the presence of functional groups that corresponded to the sericin and gelatin components. The tensile strength of the bioplastic material was measured to be 27.64 MPa/psi, while its thickness varied between 0.072 and 0.316 mm. The results of burial experiments indicated that the bioplastic material had a degradation rate of 85% after 14 days. The invention exhibits potential as a viable alternative for packaging, containment, and disposable plastic materials. The use of this sustainable approach is recommended for the extraction of sericin and gelatin from silk cocoons and fish waste, with the intention of using them as raw materials for bioplastic production.

Redox imbalance accompanies loss of viability in seeds of two cacti species buried in situ

Abstract This work provides insights into the deterioration of cacti seeds of Escontria chiotilla (F.A.C. Weber ex K. Schum) and Stenocereus pruinosus (Otto ex Pfeiff.) Buxbaum stored ex situ at 25 °C, under dry and dark conditions or buried in situ conditions in a xerophytic shrubland. Viability, germination speed, electrolyte leakage and indicators of the redox balance including glutathione content, glutathione half-cell reduction potential (EGSSG/2GSH) and malondialdehyde (MDA), oxidized protein content, together with water-soluble antioxidant enzyme activity were assessed. Over a period of two years of storage, viability was maintained when seeds were stored ex situ at 7–9% water content compared to seeds buried in the soil. A second burial experiment showed that seeds of E. chiotilla maintained viability during a year of storage that included a rainy season followed by a dry season. Thereafter, they died rapidly during the second rainy season. In contrast, those of S. pruinosus started to lose viability after 6 months of burial at the end of the rainy season and were mostly dead at the end of the dry season. This difference in persistence between species was related to a difference in the glutathione content and antioxidant enzyme activities. In both storage experiments, the loss of viability of both species was associated to a EGSSG/2GSH shift to a more oxidative state during burial. Yet, contents in MDA and oxidized soluble proteins were not related to redox imbalance and loss of viability, indicating that these compounds are not good markers of oxidative stress in cacti seeds during storage.

Design and Experiment of In Situ Soil-Lifting Shovel for Direct-Injection Straw Deep-Burial Machine

A direct-injection straw deep-burial method was proposed to address the issues of insufficient depth and compaction during the process of straw deep burial. Based on the working principle of oblique cutting, an in situ soil-lifting shovel is designed for oblique cutting of soil and in situ lifting of soil, forming a deep burial space for straw. Elaborating on the working principle of the in situ soil-lifting shovel, we analyzed the stress situation of each stage during the operation process and determined the structural parameter values of the in situ soil-lifting shovel. Using the DEM simulation analysis method, the regression orthogonal simulation test is carried out with the soil-opening angle, the soil-lifting angle, and the camber angle of the in situ soil-lifting shovel as the test indicators, and the number of straws deeply buried and the operational resistance as the evaluation indicators. The regression equation and the response surface mathematical model were established to analyze the influence of the interaction of various factors on the operational performance of the in situ soil-lifting shovel. The simulation results showed that the significant order of effect on the number of straws buried deeply and the operational resistance was camber angle > soil-opening angle > soil-lifting angle. After optimization, the structural parameters were soil-opening angle of 17°, soil-lifting angle of 37°, camber angle of 30°, the corresponding number of straw buried was 228.29, and the operating resistance was 2840.45 N. The average value of operational resistance obtained from the field validation test was 3145.95 N, and the error with the simulation results was only 11%. The quantity of straw buried deeply was 90.21%. The straw deep burial experiment further indicates that the operation effect meets the agronomic requirements of straw deep burial.

Morphology and functional properties of gelatin‐based films modified by UV radiation and bacterial cellulose nanofibers

AbstractIn the present study, the properties of biodegradable gelatin‐based films were modified by UV treatment and the incorporation of 1% (w/w) of bacterial cellulose (BC) nanofibers. UVC light was applied at different exposure times (0, 0.5, 1, and 2 h) into the film‐forming solutions. In order to evaluate the synergistic effects of these two treatments, the optimal UV condition was also applied to BC‐reinforced solutions. Films were characterized by their physicochemical, mechanical, barrier, optical, thermal, and morphological properties. Results showed that the UV treatment applied for 2 h significantly reduced the water solubility (WS) but did not affect the water vapor permeability (WVP). On the other hand, the incorporation of BC reduced WS and WVP values by 15% and 43%, respectively. Regarding mechanical properties, both treatments significantly reduced film elongation at break. However, the tensile strength (TS) and Young's modulus (YM) were only affected by UV treatment. For the film exposed to the longest treatment time, TS increased from 1.56 MPa (control) to 2.85 MPa, and YM increased from 4.36 MPa (control) to 9.23 MPa. Overall, SEM results showed that all samples had a uniform surface and a cohesive matrix. However, BC‐reinforced films showed some additional clusters, which significantly increased opacity values. Regardless of their composition, all gelatin‐based films lost their integrity after a 12‐day soil burial experiment. Film thickness, moisture content, and color parameters were not affected by any treatment. Furthermore, no synergistic effects were detected.Practical applicationsBiopolymer films and coatings are promising systems to ensure shelf life, quality, and food safety, representing a sustainable alternative to replace traditional petroleum‐based materials. Although these films have advantages, mainly due to their biodegradability, their properties are not competitive at an industrial level and need to be improved. Therefore, several studies have investigated the application of physical treatments and new process methodologies to overcome these limitations. The present study evaluated the potential use of UV radiation and bacterial cellulose nanofibers in the development of gelatin‐based films. Overall, the results showed that these methods are capable of modifying the properties and structure of films, thus offering an alternative to conventional methods of film production. Mastering the use of advanced technologies for film development could be the key to tailoring biopolymer films and coatings for specific industrial applications.

Development and characterization of starch‑sodium alginate-montmorillonite biodegradable antibacterial films

The biodegradable antibacterial composite film blended with starch and sodium alginate was developed by solution casting method, using montmorillonite as the fortifier and star anise oil as the bacteriostat. Infrared analysis showed that montmorillonite and star anise oil were successfully incorporated into starch and sodium alginate to form a stable composite film. The addition of 6 wt% montmorillonite could enhance several properties of the films, including barrier properties, optical properties, thermal stability and mechanical properties. Meanwhile, the incorporation of star anise oil made the composite films have antibacterial properties to resist E. coli. Packing cherry tomatoes with starch‑sodium alginate-montmorillonite-star anise oil composite film could reduce the weight loss rate and decay rate of fresh cherry tomatoes. Soil burial experiments showed that the composite films exhibited a continuous biodegradation process. The starch‑sodium alginate-montmorillonite-star anise oil films decomposed into little pieces and were completely mixed in the soil within 22 days, which offered an application foreground for the development of biodegradable food packaging film with bacteriostatic activity.

Statistical inference for seed mortality and germination with seed bank experiments.

Plant population ecologists regularly study soil seed banks with seed bag burial and seed addition experiments. These experiments contribute crucial data to demographic models, but we lack standard methods to analyze them. Here, we propose statistical models to estimate seed mortality and germination with observations from these experiments. We develop these models following the principles of event history analysis, and analyze their identifiability and statistical properties by algebraic methods and simulation. We demonstrate that seed bag burial, but not seed addition experiments, can be used to make inferences about age-dependent mortality and germination. When mortality and germination do not change with seed age, both experiments produce unbiased estimates but seed bag burial experiments are more precise. However, seed mortality and germination estimates may be inaccurate when the statistical model that is fit makes incorrect assumptions about the age dependence of mortality and germination. The statistical models and simulations that we present here can be adopted and modified by plant population ecologists to strengthen inferences about seed mortality and germination in the soil seed bank.

Effect of substratum types on the growth of assimilators and stolons of <italic>Caulerpa okamurae</italic> (Bryopsidales, Chlorophyta)

To examine the effects of substratum types on the growth of Caulerpa okamurae, sand surface and sand burial experiments were conducted. Five assimilators (erect fronds) per replicate were cultured for 15 d on the surface of three different treatments: fine sand (200 μm), coarse sand (600 μm), and no sand (control). Also, three stolons and three assimilators were buried by fine grain or coarse grain sands and incubated for 15 d. In both experiments, other culture conditions included 25°C, 30 μmol photons m-2 s-1, and 16 : 8 h L : D (light : dark). In both experiments, stolon + assimilator-, assimilator-, and stolon-weights were measured. Relative growth rates (RGRs) of stolon + assimilator weights ranged from 0.43 to 1.95% d-1 at no sand and fine sand treatment, respectively. RGRs for the weight of stolon + assimilator and new assimilators were significantly greater on the fine- and coarse sand surface than the control. In the burial experiments, RGRs of stolons (4.28% d-1 at coarse sand and 5.57% d-1 at fine sand, respectively) were significantly greater than those of assimilators (1.38% d-1 at fine sand and 1.82% d-1 at coarse sand, respectively). When stolons were buried, RGRs for assimilators were greater at the fine sand than at the coarse sand treatment. On the other hand, RGRs of buried assimilators for total frond weights and for newly produced stolons were significantly greater at the coarse sands than at the fine sands. In conclusion, C. okamurae grew well with all substrates of sands and showed better growth on fine sands than coarse ones. This result suggests that the growth of stolons and assimilators of C. okamurae is stimulated after stable attachment to the sand substrates by rhizophores. In addition, stolons showed higher growth rates than the assimilators in the sand burial states, indicating that stolons are more tolerant to low light than assimilators of C. okamurae.

Effect of stacking sequence on mechanical, water absorption, and biodegradable properties of novel hybrid composites for structural applications

Abstract This study used a hand layup process to create tri-layer hybrid composites composed of snake grass fiber (SGF) and jute fiber (JF). Two types of hybrid composites were investigated: jute/snake grass/jute (J/S/J) and snake grass/jute/snake grass (S/J/S). The fabricated composites were subjected to mechanical characterization and water absorption studies to verify their compatibility for various applications. The outcome revealed that the J/S/J hybrid sample shows the highest tensile and flexural strength at 68.46 and 78.62 MPa, respectively. This is due to stacking the maximum-strength JF as an exterior layer in the hybrid J/S/J sample. Meanwhile, the S/J/S composite shows a very high impact strength value of 4.45 kJ/mm2 due to the placement of SGF at the outermost layer. It leads to absorbing more impact energy at sudden load applications. Water absorption studies revealed that the S/J/S composite absorbed more moisture than the J/S/J composite. Furthermore, the S/J/S composite exhibited greater biodegradability than the J/S/J composite based on soil burial experiments. From this study, it can be concluded that the J/S/J composite is suitable for structural applications because it has higher tensile and flexural qualities. In contrast, the S/J/S composite can be employed under damping conditions because it has better impact strength.

Biodegradable and Biobased Mulch Films: Highly Stretchable PLA Composites with Different Industrial Vegetable Waste.

Highly stretchable biobased and biodegradable agricultural mulch films based on polylactic acid (PLA) and 10, 20, or 30 wt % various nonedible vegetable wastes such as spinach stems (SS), tomato pomace (TP), and cocoa shells (CS) are prepared and characterized in this work. The results demonstrate that appropriate PLA plasticization and vegetable waste addition allow for obtaining films suitable for mulching with tensile strengths in the 10–24 MPa range and elongations at break up to 460%, depending on the kind and amount of vegetable waste incorporated. Additionally, the developed mulches show low water solubility (1–15 wt %) and moisture content (1–3 wt %) with a water vapor permeability of up to 3 × 10–10 g s–1 m–1 Pa–1, similar to that of Mater-Bi. In addition, the type of vegetable waste added as filler were demonstrated to significantly affect not only the films’ mentioned properties but also their biodegradability. For instance, films prepared with 20 wt % SS were demonstrated to improve PLA soil biodegradability, which increased from 0 to 38 wt % for PLA composites after 6 months of a soil burial experiment. Lastly, the developed composites contain different amounts of plant micro- and macronutrients, indicating their potential as fertilizers. The results found in this work represent a sustainable, fully biobased alternative to other mulches already in the market.

Long-term seed burial reveals differences in the seed-banking strategies of naturalized and invasive alien herbs

Soil seed viability and germinability dynamics can have a major influence on the establishment and spread of plants introduced beyond their native distribution range. Yet, we lack information on how temporal variability in these traits could affect the invasion process. To address this issue, we conducted an 8-year seed burial experiment examining seed viability and germinability dynamics for 21 invasive and 38 naturalized herbs in the Czech Republic. Seeds of most naturalized and invasive species persisted in the soil for several years. However, naturalized herbs exhibited greater seed longevity, on average, than invasive ones. Phylogenetic logistic models showed that seed viability (but not germinability) dynamics were significantly related to the invasion status of the study species. Seed viability declined earlier and more sharply in invasive species, and the probability of finding viable seeds of invasive species by the end of the experiment was low. Our findings suggest that invasive herbs might take advantage of high seed viability in the years immediately after dispersal, while naturalized species benefit from extended seed viability over time. These differences, however, are not sufficiently strong to explain the invasiveness of the species examined.

Controlled preparation of grafted starch modified with Ni nanoparticles for biodegradable polymer nanocomposites and its application in food packaging.

Grafting of starch with methyl methacrylate was carried out using a free radical mechanism. Free radicals were generated by the thermal disintegration of potassium persulphate at the temperature of 60°C. A variety of experimental methods were investigated to check the effect of different parameters such as (temperature, amount of starch, quantity of monomer) for efficient grafting. The optimum temperature found for good grafting was 60°C. The initial amount of starch was taken as 0.75 g. Keeping the amount of starch constant, the quantity of monomer was reduced gradually from 10 to 2ml in portions of 5 and 3ml. The controlled biodegradability of the grafted product was obtained by using a 3ml monomer in 0.75 g starch. This grafted polymer showed 31.45% biodegradability in 60 days. The nanocomposite of starch grafted methyl methacrylate was prepared by incorporating 0.02 g Ni nanoparticles in the reaction flask 15 min before the completion of reaction time. The starch grafted polymer and nanocomposite of this were fully characterized by SEM, FTIR, TGA, and DSC techniques. The soil burial method was applied to estimate the biodegradability of samples. The polymer containing Ni nanoparticles was less biodegradable than without nanoparticles. Such polymers can be efficiently used as packaging material for food items. RESEARCH HIGHLIGHTS: Through a free radical method, methyl methacrylate was grafted onto the backbone of starch in this study. During the process, nickel nanoparticles were added to achieve the nickel nanocomposite of the starch grafted polymer. The breakdown of starch grafted polymer after 60 days in a soil burial experiment was 31.45%, whereas the degradation of nanocomposites was 20.07%. Our synthesized nanocomposite polymers can be effectively employed as packaging material for food items.

The preparation and performance of poly(butylene adipate) terephthalate/corn stalk composites

Poly (butylene adipate) terephthalate (PBAT) and corn stalk (CS) are both biodegradable materials. The high cost of PBAT limits its range of applications. In this paper, a biodegradable composite was prepared by melt-blending PBAT with CS as a filler. PBAT and different amounts of CS were melted in an internal mixer. The compatibility of CS with PBAT or with a modified PBAT (MPBAT) and its dispersion in either of them were studied by scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis, and other test methods. The properties of PBAT/CS or MPBAT/CS composites were investigated by evaluating the following: mechanical properties, contact angle, water absorption, oxygen permeability, and water vapor permeability. It was found that CS and MPBAT had good compatibility. The results from soil burial experiment results showed that the biodegradability of the two composites increased with CS. CS showed great potential in biomass composites. Compared with PBAT/CS composites, MPBAT/CS composites had higher tensile properties and better barrier ability. The introduction of biomass fillers in MPBAT would promote the application of biodegradable materials in the field of environmentally friendly packaging materials.

Seed persistence of three species, Carex stricta, Carex hystericina and Phalaris arundinacea, in a restored wetland

Seed persistence and longevity is poorly documented for wetland plants, despite the value of this knowledge for restoration. Seed persistence is particularly important information for sedge meadows (i.e., seasonally ponded freshwater wetlands dominated by Carex spp.), which often fail to recolonize without planting and are rapidly invaded by reed canary grass (Phalaris arundinacea L.). We conducted a 17-year seed burial study along a hydrological gradient in a Minnesota wetland to assess seed persistence of P. arundinacea and two common species of sedge meadows, bottlebrush sedge (Carex hystericina Muhl. ex Willd.) and upright sedge (Carex stricta Lam.). Seed samples were placed in capsules designed to prevent seed loss while allowing for environmental influences. Six boxes, each containing 126 seed capsules (3 species x 14 exhumation years x 3 replicates), were buried in wetland soils under three hydrological conditions (regularly, seasonally, or never inundated) along two transects. Seeds were exhumed 1-, 5-, 6-, 9-, and 17-years post-burial and tested for germinability and viability. For C. stricta and P. arundinacea, seed persistence (50% survival, P50) was < 1 year under all hydrologic conditions, while for C. hystericina P50 was 6 yrs where never inundated and > 17 years when seasonally or regularly inundated. Seed longevity was < 17 yrs for C. stricta and P. arundinacea in locations never inundated; for other hydrological conditions and for C. hystericina, seed longevity exceeded the duration of the burial experiment. If seed persistence is typically reduced where inundation is brief, sedge meadow wetlands drained and cultivated for many decades are unlikely to have long-buried seed banks to serve as propagule sources for revegetation.

A quantitative analysis of primary dormancy and dormancy changes during burial in seeds of Brassica napus

For plants inhabiting unpredictable environments, scheduling germination can be challenging. Various responses to environmental conditions have been evolved by plants; these responses combine with variation in local climate to construct germination niche. Germination process may be regulated by a number of factors, among them, the type of seed dormancy and dormancy cycling play an important role in promoting survival after dispersal. In the present study, seeds of Brassica napus were tested for primary conditional dormancy (CD). Dormancy changes were quantified through seed population thermal germination parameters to test whether different genotypes of B. napus seeds (944, 966, Alestrom, Danube, Okanto and Rohan) are non‐dormant (ND) at the maturity or if they present primary dormancy (D or CD). In a burial experiment, B. napus seeds dormancy cycling in the natural soil seedbank was investigated. Germination of all genotypes decreased at 5 and &gt; 20°C, showing narrower breadth of thermal niche for germination. Dormancy‐breaking treatments lead to the widening of thermal range permissive for germination. The lower limit (Tl(50)) and higher limit (Th(50)) temperatures for germination decreased and increased, respectively, for non‐dormant (after‐ripened seeds treated with GA3) seeds compared with fresh seeds in all genotypes. In fresh seeds, the Tl(50) and Th(50) for various genotypes ranged from 3.61 to 6.5°C and 25.0 to 29.0°C, respectively and ranged from 0.2 to 1.8°C and 35 to 41.0°C in non‐dormant seeds. Thus, fresh seeds of B. napus are dormant at dispersal and adopt delayed germination strategies to avoid summer drought. In the burial experiment, the results indicated that B. napus must have D/ND cycle in which fresh seeds first become dormant and then the cycle begins (CD→D↔CD↔ND), thus adopting both risk‐prone and risk‐adverse strategies to spread the likelihood of survival over time.

Is there an effect of storage depth on the persistence of silver birch (Betula pendula Roth) and rowan (Sorbus aucuparia L.) seeds? A seed burial experiment

Sorbus aucuparia L. (rowan) and Betula spp. (birch) are the most common of the early successional pioneer tree species in central Europe with the ability to form a soil seed bank. Little is known about the reasons for the high variations observed in the persistence in the soil of rowan and birch seeds. The objective of this study was to assess the ability of buried birch and rowan seeds to form short-term persistent soil seed banks and to analyse the influence of burial depth on seed persistence. An artificial seed burial experiment was initiated to study the persistence of birch seeds and rowan seeds, with and without pulp, stored at depths of 2, 5 and 10 cm in mineral soil over 2.5 years. The predicted maximum storability periods for buried birch seeds was 13 years, compared to 4.5 years for rowan seeds with pulp and 3.5 years without pulp. The lower storage capacity of rowan seeds was demonstrated by germinations in the darkness within soil of 3-22% of seeds without pulp and 4-48% of seeds with pulp. Germination percentages of birch and rowan with and without pulp did not differ between depths. Only burial duration had an effect for either tree species. Birch and rowan seeds are able to form short-term persistent soil seed banks. Birch accumulates a seed reserve in the soil over time, until a change in conditions conducive to germination occurs, while rowan seeds germinate promptly after overcoming seed dormancy. The pulp provides no benefits in relation to the persistence of rowan seeds; rather, it appears to act as a physical inhibitor of germination. Therefore, annual input of fresh seeds is required for the success of rowan. Seed input every few years seems sufficient to guarantee a minimum number of viable birch seeds.

Water resistance and biodegradation properties of conventionally-heated and microwave-cured cross-linked cellulose nanocrystal/chitosan composite films

The cross-linking of cellulose nanocrystals (CNC)/chitosan composite films with glutaraldehyde (GA) as the cross-linking agent, was carried out by using conventional heating and microwave curing, respectively. The addition of 5 wt% CNC has significantly reduced the water vapor permeability (WVP) of chitosan films by 30% compared to the neat chitosan film. The decline in the swelling and solubility were also observed in the CNC/chitosan composite films. Moreover, the cross-linking has further enhanced the water resistance by reducing the WVP, swelling and solubility of CNC/chitosan films, especially for microwave-cured GA-cross-linked CNC/chitosan films. The biodegradation testing was performed by the soil burial experiment. The cross-linked chitosan composite films were found to have a lower degradability rate compared with the uncross-linked composites especially for the microwave-cured CNC/chitosan composite films. The composite films-degrading microorganisms were identified as Ophiocordyceps heteropoda, Enterobacter kobei and E. roggenkampii, by the molecular analysis via polymerase chain reaction and DNA sequencing. This study demonstrated that the CNC/chitosan composite films especially microwave-cured composite films could be the suitable materials to be employed as the food packaging with outstanding water resistance property and moderate biodegradability.

Impact of Seasonal Variations on the Colonial Populations of Bacteria and Fungi in Soil and on Buried Plant Stems

Forest soils and stems buried in them usually have varying degrees of colonization and abundance of bacteria and fungi. This study was undertaken to determine the effects of seasonal variations on the population of bacteria and fungi isolated from forest soil and on plant stems buried in the soil. Soil sampling and stem burial studies were conducted over a 12-month period in 2019. Serially diluted soil samples were plated on suitable media for bacterial and fungal growth and thereafter counted after incubation. Buried stems were removed from the soil, rinsed and placed in flasks containing suitable media for fungal and bacterial cultivation. Colonial growth was counted after incubation. Soil moisture was highest during the wet season months of July (27.7%), August (23.5 %), September 26.1 %) and October (29 %) whereas the average soil moisture content was lowest in the dry season. Seasonal pH did not significantly affect microbial population levels in the various months. Colony counts for Pseudomonas spp. during the dry season months (January, February, March and April) were very low. Growth of the bacterium showed peaks in the May through October during which counts reached 109 cells per gram of soil except in August with counts of 108 cells per gram of soil. Micrococcus spp. and Bacillus spp. also showed similar trends in colony counts with little variations. Fungi were generally fewer in number than bacteria and only one peak which reached 107 cells/g soil was obtained for Fusarium spp. and Rhizopus spp. in September and October respectively. The density of Trichoderma spp. per gram of soil peaked at 106 cells in June, July, September and October. Counts for Aspergillus spp. was negligible in January, February, March and April but reached 106 cells per gram of soil in June, July and August. The colonization of Pseudomonas spp. on buried plant stem varied between 62% in June to 76% in October while Micrococcus spp. had levels which varied from 65% in May to 84% in June and 72% in October. Fusarium species were found most frequently on the stem every month except in February, March and April. Low colonization of Aspergillus spp. on stems occurred in January, February, March, November and December. Highest numbers of this organism was found in August, September and October. Rhizopus spp. was observed in 85 and 80% of the stem in September and October respectively but lower percentages of colonization occurred in January, February, March and April. In all the dry season months (January-April), all bacterial and fungal populations had low densities but their counts increased in the rainy season. Fungi were generally fewer in number than bacteria in both soil and stem burial experiments.

Responses of soil microbiome to steel corrosion

The process of microbiologically influenced corrosion (MIC) in soils has received widespread attention. Herein, long-term outdoor soil burial experiments were conducted to elucidate the community composition and functional interaction of soil microorganisms associated with metal corrosion. The results indicated that iron-oxidizing (e.g., Gallionella), nitrifying (e.g., Nitrospira), and denitrifying (e.g., Hydrogenophaga) microorganisms were significantly enriched in response to metal corrosion and were positively correlated with the metal mass loss. Corrosion process may promote the preferential growth of the abundant microbes. The functional annotation revealed that the metabolic processes of nitrogen cycling and electron transfer pathways were strengthened, and also that the corrosion of metals in soil was closely associated with the biogeochemical cycling of iron and nitrogen elements and extracellular electron transfer. Niche disturbance of microbial communities induced by the buried metals facilitated the synergetic effect of the major MIC participants. The co-occurrence network analysis suggested possible niche correlations among corrosion related bioindicators.