ZhiJian Zhang

Genetic Linkage of Soil Carbon Pools and Microbial Functions in Subtropical Freshwater Wetlands in Response to Experimental Warming

ABSTRACT Rising climate temperatures in the future are predicted to accelerate the microbial decomposition of soil organic matter. A field microcosm experiment was carried out to examine the impact of soil warming in freshwater wetlands on different organic carbon (C) pools and associated microbial functional responses. GeoChip 4.0, a functional gene microarray, was used to determine microbial gene diversity and functional potential for C degradation. Experimental warming significantly increased soil pore water dissolved organic C and phosphorus (P) concentrations, leading to a higher potential for C emission and P export. Such losses of total organic C stored in soil could be traced back to the decomposition of recalcitrant organic C. Warming preferentially stimulated genes for degrading recalcitrant C over labile C. This was especially true for genes encoding cellobiase and mnp for cellulose and lignin degradation, respectively. We confirmed this with warming-enhanced polyphenol oxidase and peroxidase activities for recalcitrant C acquisition and greater increases in recalcitrant C use efficiency than in labile C use efficiency (average percentage increases of 48% versus 28%, respectively). The relative abundance of lignin-degrading genes increased by 15% under warming; meanwhile, soil fungi, as the primary decomposers of lignin, were greater in abundance by 27%. This work suggests that future warming may enhance the potential for accelerated fungal decomposition of lignin-like compounds, leading to greater microbially mediated C losses than previously estimated in freshwater wetlands.

Phosphorus fluxes at the sediment-water interface in subtropical wetlands subjected to experimental warming: A microcosm study

Global warming is increasingly challenging for wetland ecological function. A temperature controlled microcosm system was developed to simulate climate change scenarios of an ambient temperature (control) and an elevated temperature (+5 °C). The effects and associated mechanisms of warming on phosphorus (P) fluxes at the sediment-water interface of six subtropical wetlands were investigated. The results indicated that P fluxes were generally enhanced under the experimental warming as measured by higher P concentrations in the porewater and overlying water as well as higher benthic P fluxes. The release of P from sediment to porewater occurred more strongly and quickly in response to experimental warming compared to the subsequent upward transfer into overlying water. The average accumulative benthic P output from the tested wetlands under the experimental warming was greater by 12.9 μg cm(-2) y(-1) (28%) for total P and 8.26 μg cm(-2) y(-1) (25%) for dissolved reactive P, compared to the ambient scenarios. Under warming the redistribution of P fractions in sediments occurred with greater NH(4)Cl-P and lower BD-P (extracted by a bicarbonate buffered dithionite solution) accompanied by greater NaOH-P. The higher temperature enhanced total phospholipid fatty acids. A shift in the microbial community was also observed with a relative dominance of fungi (a 4.7% increase) and a relative decline (by 18%) in bacterial abundance, leading to the higher secretion of phosphatase. Comparing between wetlands, the potential P fluxes in the nutrient-enriched wetlands were less impacted by warming than the other wetland types investigated. Thus wetlands characterized by low or medium concentrations of P in sediments were more susceptible to warming compared to P-rich wetlands.

Insight into the effect of hydrogenation on efficiency of hydrothermal liquefaction and physico-chemical properties of biocrude oil.

Hydrothermal liquefaction of Nannochloropsis salina (N. salina) and larvae-vermicompost were conducted under both non-hydrogenating and hydrogenating subcritical conditions using H2 and Ni-Mo/Al2O3. Hydrogenation raised biocrude yields from 33.2% to 43.5% (vermicompost) and 55.6% to 78.5% (N. salina), whereas high heat values increased from 32.89 to 34.24 MJ/kg (vermicompost) and 36.30 to 37.53 MJ/kg (N. salina). Compared with the non-hydrogenated HTL process, the contents of acids, amides, phenols, and alcohols decreased, whereas hydrocarbons content increased. More branched cyclic nitrogenous compounds were detected in the hydrogenated biocrudes, whereas the aromatic/hetero-aromatic functionality was somewhat decreased. Smaller molecular weights and polydispersity index of the hydrogenated biocrudes were also detected. Results show that hydrogenation enhanced the removal of hydrophilic functional groups and the stabilization of radicals, thereby leading to the inhibition of loss of mass toward liquid and gaseous products and the upgrading of oil quality.

The antibiotic resistome of swine manure is significantly altered by association with the Musca domestica larvae gut microbiome

The overuse of antibiotics as veterinary feed additives is potentially contributing to a significant reservoir of antibiotic resistance in agricultural farmlands via the application of antibiotic-contaminated manure. Vermicomposting of swine manure using housefly larvae is a promising biotechnology for waste reduction and control of antibiotic pollution. To determine how vermicomposting influences antibiotic resistance traits in swine manure, we explored the resistome and associated bacterial community dynamics during larvae gut transit over 6 days of treatment. In total, 94 out of 158 antibiotic resistance genes (ARGs) were significantly attenuated (by 85%), while 23 were significantly enriched (3.9-fold) following vermicomposting. The manure-borne bacterial community showed a decrease in the relative abundance of Bacteroidetes, and an increase in Proteobacteria, specifically Ignatzschineria, following gut transit. ARG attenuation was significantly correlated with changes in microbial community succession, especially reduction in Clostridiales and Bacteroidales. Six genomes were assembled from the manure, vermicompost (final product) and gut samples, including Pseudomonas, Providencia, Enterococcus, Bacteroides and Alcanivorax. Transposon-linked ARGs were more abundant in gut-associated bacteria compared with those from manure and vermicompost. Further, ARG-transposon gene cassettes had a high degree of synteny between metagenomic assemblies from gut and vermicompost samples, highlighting the significant contribution of gut microbiota through horizontal gene transfer to the resistome of vermicompost. In conclusion, the larvae gut microbiome significantly influences manure-borne community succession and the antibiotic resistome during animal manure processing.

Concentration dynamics and biodegradability of dissolved organic matter in wetland soils subjected to experimental warming

Dissolved organic matter (DOM) is the most bioavailable soil organic pool. Understanding how DOM responds to elevated temperature is important for forecasting soil carbon (C) dynamics under climate warming. Here a 4.5-year field microcosm experiment was carried out to examine temporal DOM concentration dynamics in soil pore-water from six different subtropical wetlands. Results are compared between control (ambient temperature) and warmed (+5°C) treatments. UV-visible and fluorescence spectroscopy was performed to reveal DOM structural complexity at the end of the warming incubation. Elevated temperature resulted in initially (1 to 2.5 years) high pore-water DOM concentrations in warmed samples. These effects gradually diminished over longer time periods. Of the spectral indices, specific UV absorbance at 280 nm and humification index were significantly higher, while the signal intensity ratio of the fulvic-like to humic-like fluorescence peak was lower in warmed samples, compared to the control. Fluorescence regional integration analysis further suggested that warming enhanced the contribution of humic-like substances to DOM composition for all tested wetlands. These spectral fingerprints implied a declined fraction of readily available substrates in DOM allocated to microbial utilization in response to 4.5 years of warming. As a negative feedback, decreased DOM biodegradability may have the potential to counteract initial DOM increases and alleviate C loss in water-saturated wetland soils.

A full-scale house fly (Diptera: Muscidae) larvae bioconversion system for value-added swine manure reduction

Manure produced from confined animal farms can threaten public and environmental health if not managed properly. Herein, a full-scale commercial bioconversion operation in DeQing County, China for value-added swine manure reduction using house fly, Musca domestica L., larvae is reported. The greenhouse-assisted larvae bioreactor had a maximum daily treatment capacity of 35 m3 fresh raw manure per day. The bioconversion process produced a fresh larvae yield of 95–120 kg m3 fresh raw manure. This process provided an alternative animal foodstuff (having 56.9 and 23.8% protein and total fat as dry matter, respectively), as well as captured nutrients for agricultural re-utilization. Bioconversion reduced odour emission (characterized by 3-methylindole) and the Escherichia coli (E. coli) index by 94.5 and 92.0%, respectively, and reductions in total weight, moisture and total Kjeldahl nitrogen in solids were over 67.2, 80.0 and 76.0%, respectively. Yearly profit under this trial period ranged from US

Attenuation of veterinary antibiotics in full-scale vermicomposting of swine manure via the housefly larvae ( Musca domestica )

33.4–46.1 per m3. It is concluded that swine manure larvae bioconversion technology with subsequent production of value-added bio-products can be a promising avenue when considering a programme to reduce waste products in an intensive animal production system.

Enhanced Adsorption of Trivalent Arsenic from Water by Functionalized Diatom Silica Shells

Animal waste from concentrated swine farms is widely considered to be a source of environmental pollution, and the introduction of veterinary antibiotics in animal manure to ecosystems is rapidly becoming a major public health concern. A housefly larvae (Musca domestica) vermireactor has been increasingly adopted for swine manure value-added bioconversion and pollution control, but few studies have investigated its efficiency on antibiotic attenuation during manure vermicomposting. In this study we explored the capacity and related attenuation mechanisms of antibiotic degradation and its linkage with waste reduction by field sampling during a typical cycle (6 days) of full-scale larvae manure vermicomposting. Nine antibiotics were dramatically removed during the 6-day vermicomposting process, including tetracyclines, sulfonamides, and fluoroquinolones. Of these, oxytetracycline and ciprofloxacin exhibited the greater reduction rate of 23.8 and 32.9 mg m−2, respectively. Environmental temperature, pH, and total phosphorus were negatively linked to the level of residual antibiotics, while organic matter, total Kjeldahl nitrogen, microbial respiration intensity, and moisture exhibited a positive effect. Pyrosequencing data revealed that the dominant phyla related to Firmicutes, Bacteroidetes, and Proteobacteria accelerated manure biodegradation likely through enzyme catalytic reactions, which may enhance antibiotic attenuation during vermicomposting.

Exogenous Phosphorus Inputs Alter Complexity of Soil-Dissolved Organic Carbon in Agricultural Riparian Wetlands

The potential of porous diatom silica shells as a naturally abundant low-cost sorbent for the removal of arsenic in aqueous solutions was investigated in a batch study. The objective of this work was to chemically modify the silica shells of a diatom Melosira sp. with bifunctional (thiol and amino) groups to effectively remove arsenic in its toxic As(III) form (arsenite) predominant in the aquatic environment. Sorption experiments with this novel sorbent were conducted under varying conditions of pH, time, dosage, and As(III) concentration. A maximum adsorption capacity of 10.99 mg g-1 was achieved within 26 h for a solution containing 12 mg L-1 As(III) at pH 4 and sorbent dosage of 2 g L-1. The functionalized diatom silica shells had a surface morphological change which was accompanied by increased pore size at the expense of reduced specific surface area and total pore volume. As(III) adsorption was best fitted with the Langmuir-Freundlich model, and the adsorption kinetic data using pore surface diffusion model showed that both the external (film) and internal (intraparticle) diffusion can be rate-determining for As(III) adsorption. Fourier transform infrared spectroscopy (FTIR) indicated that the thiol and amino groups potentially responsible for As(III) adsorption were grafted on the surface of diatom silica shells. X-ray photoelectron spectroscopy (XPS) further verified that this unique sorbent proceeded via a chemisorption mechanism through the exchange between oxygen-containing groups of neutral As(III) and thiol groups, and through the surface complexation between As(III) and protonated nitrogen and hydroxyl groups. Results indicate that this functionalized bioadsorbent with a high As(III) adsorption capacity holds promise for the treatment of As(III) containing wastewater.

Influences of nitrification inhibitor 3,4-dimethyl pyrazole phosphate on nitrogen and soil salt-ion leaching

High-strengthened farmland fertilization leads to mass inputs of nutrients and elements to agricultural riparian wetlands. The dissolved organic carbon (DOC) of such wetland sediments is an important intermediate in global carbon (C) cycling due to its role in connecting soil C pools with atmospheric CO2. But the impact of phosphorus (P) on sediment DOC is still largely unknown, despite increasing investigations to emphasize P interception by riparian wetlands. Here, we simulated the temporal influences of exogenous P on sediment DOC of riparian wetlands by integrating gradient P loading at rates of 0%, 5%, 10%, 20%, 30%, and 60% relative to the initial total phosphorus content of the sediment with the purpose of illustrating the role of external P on the complexity of soil DOC in terms of its amount and composition. After incubating for nine months, a dramatic linear correlation between Olsen-P and fluorescent and ultraviolet spectral indices considered DOC skeleton was observed. Together with a more microbial-derived origin of DOC and a reduction of DOC aromaticity or humicity, the excitation-emission matrix had shown a blue shift reflecting a trend towards a simpler molecular structure of sediment DOC after P addition. Meanwhile, the content of soil DOC and its ratio with total organic carbon (TOC) were also increased by P loading, coupled with enhanced values of highly labile organic carbon and two C-related enzymes. While TOC and recalcitrant organic carbon decreased significantly. Such implications of DOC amounts and composition stimulated by external P loading may enhance its bioavailability, thereby inducing an accelerated effect on soil C cycling and a potential C loss in response to global climate change.