This study evaluates the potential of manure-derived biochars in promoting plant growth and enhancing soil chemical and biological properties during a 150day pot experiment. Biochars from pyrolysis ...of poultry litter (PL) and swine manure (SM) at 400 and 600°C, and a commonly available wood chip (WC) biochar produced at high temperature (1000°C) were incorporated to silt-loam (SL) and sandy (SY) soils on a 2% dry soil weight basis. Ryegrass was sown and moisture was adjusted to 60% water filled pore space (WFPS). The PL400 and SM400 biochars significantly increased (p<0.05) shoot dry matter (DM) yields (SL soil) and enhanced nitrogen (N), phosphorus (P) and potassium (K) uptake by the plants in both soils, compared to the Control. All biochars significantly increased the soil carbon (C) contents compared to the Control. Total N contents were significantly greater for PL400 and PL600 treatments in both soils. The dehydrogenase activity (DA) significantly increased for PL400 and SM400 treatments and was positively correlated with the volatile matter (VM) contents of the biochars, while β-glucosidase activity (GA) decreased for the same treatments in both soils. All biochars significantly shifted (p≤0.05) the bacterial community structure compared to the Control. This study suggests that pyrolysis of animal manures can produce a biochar that acts as both soil amendment and an organic fertilizer as proven by increased NPK uptake, positive liming effect and high soil nutrient availability, while WC biochar could work only in combination with fertilizers (organic as well as mineral).
Picture 1 Graphical abstract highlighting “Chemically and biologically-mediated fertilizing value of manure-derived biochars”. Display omitted
•Low temperature manure biochars enhanced DM yield, NPK uptake, and soil properties.•More positive effects of biochars on acidic silt-loam than on alkaline sandy soil.•Wood biochar had no effect on DM yield but showed a good C sequestration potential.•All biochars shifted bacterial community structure and modified enzyme activities.
Trees and their associated rhizosphere organisms play a major role in mineral weathering driving calcium fluxes from the continents to the oceans that ultimately control long-term atmospheric CO2 and ...climate through the geochemical carbon cycle. Photosynthate allocation to tree roots and their mycorrhizal fungi is hypothesized to fuel the active secretion of protons and organic chelators that enhance calcium dissolution at fungal-mineral interfaces. This was tested using (14)CO2 supplied to shoots of Pinus sylvestris ectomycorrhizal with the widespread fungus Paxillus involutus in monoxenic microcosms, revealing preferential allocation by the fungus of plant photoassimilate to weather grains of limestone and silicates each with a combined calcium and magnesium content of over 10 wt.%. Hyphae had acidic surfaces and linear accumulation of weathered calcium with secreted oxalate, increasing significantly in sequence: quartz, granite < basalt, olivine, limestone < gabbro. These findings confirmed the role of mineral-specific oxalate exudation in ectomycorrhizal weathering to dissolve calcium bearing minerals, thus contributing to the geochemical carbon cycle.
Soil amendments with biochar to improve soil fertility and increase soil carbon stocks have received some high-level attention. Physical and chemical analyses of amended soils and biochars from ...various feedstocks are reported, alongside some evaluations of plant growth promotion capabilities. Fewer studies investigated the soil microbiota and their potential to increase cycling and mobilization of nutrients in biochar-amended soils. This review is discussing the latest findings in the bacterial contribution to cycling and mobilizing nitrogen, phosphorus, and sulfur in biochar-amended soils and potential contributions to plant growth promotion. Depending on feedstock, pyrolysis, soil type, and plant cover, changes in the bacterial community structure were observed for a majority of the studies using amplicon sequencing or genetic fingerprinting methods. Prokaryotic nitrification largely depends on the availability of ammonium and can vary considerably under soil biochar amendment. However, denitrification to di-nitrogen and in particular, nitrous oxide reductase activity is commonly enhanced, resulting in reduced nitrous oxide emissions. Likewise, bacterial fixation of di-nitrogen appears to be regularly enhanced. A paucity of studies suggests that bacterial mobilization of phosphorus and sulfur is enhanced as well. However, most studies only tested for extracellular sulfatase and phosphatase activity. Further research is needed to reveal details of the bacterial nutrient mobilizing capabilities and this is in particular the case for the mobilization of phosphorus and sulfur.
•Biochar soil amendment significantly promoted growth of spring barley.•Biochar soil amendment significantly altered bacterial community structures.•S and P mobilizing bacterial abundances ...significantly increased with biochar addition.•Stepwise regression attributed 74% of plant growth to P and S mobilizing bacteria.•Pyrolysis of Miscanthus grass produced biochar with sulfate ester as main S source.
Biochar has shown great potentials in plant growth promotion but its effect on soil bacteria that potentially support plant growth is less well understood. In this study, the effect of biochar soil amendment was investigated on the growth of spring barley, its rhizobacteria diversity and the abundance of sulfur (S) and phosphorus (P) mobilizing bacteria. Furthermore, the S oxidation status was determined in soil, feedstock and biochar. Soil amendment with biochar made from Miscanthus x giganteus resulted in significantly increased growth of barley and grain formation four to seven fold. Further significant increases were found for the soil pH and abundances of rhizosphere soil bacteria capable of growing with tri-calcium phosphate, phosphate-esters, phosphonates or aromatic sulfonates as sole source of S or P. A stepwise regression model attributed 74% of the variation in plant growth to the abundances of P and S mobilizing bacteria. 16S rRNA gene based fingerprint analysis revealed a significant shift in the bacterial community structure upon biochar amendment that correlated significantly with the above mentioned changes (pH, plant growth, bacterial abundances). Under biochar amendment, up to 100 times increases in genera Brevundimonas known for P cycling and Arthrobacter and Cupriavidus previously involved in sulfonate desulfurization were identified via quantitative PCR. S k-edge XANES confirmed that the key S source sulfonate was largely absent in the applied biochar, thus bacterial mobilization of sulfonate-S may have originated from the soil.
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•Thyme EO and verbenone are effective anti-listerial agents on melon and pineapple.•Direct application of anti-listerial agents on fruits is more effective than dipping.•Verbenone is ...maintaining a high product appearance for melon while thyme EO is not.•EO and EO compounds on lettuce reduce product appearance beyond acceptance levels.•Modified atmosphere packaging has limited effect on L. monocytogenes growth/survival.
The anti-listerial effectiveness of thyme essential oil (EO) and EO compounds camphor and verbenone was examined on fresh-cut lettuce, cantaloupe melon and pineapple with modified atmospheres and air in model packages at 4 and 8°C. Listeria monocytogenes was found to be able to survive and grow in all atmospheres on melon and lettuce. However, on pineapple lowest survival was identified, presumably due to product pH. Thyme EO demonstrated the best anti-listerial effect, although direct application of the EO compromised product appearance. While camphor showed no anti-listerial effects, verbenone was found to have anti-listerial properties and maintained high sensory acceptance in fresh-cut fruit. The high growth rates of L. monocytogenes on melon were significantly reduced with the application of verbenone while being completely eliminated on pineapple. The use of thyme EO and verbenone as an antimicrobial dip was successfully applied to reduce growth of Listeria on fresh-cut melon and eliminate growth on pineapple; however growth-reduction was less pronounced in melon when compared to a conventional chlorine dip. Further research will be necessary to optimise conditions in fresh-cut produce treatments with natural products including verbenone and thyme EO to replace current chlorine treatments for improved food safety.
Sulfonates are major soil sulfur components that can be desulfurized by certain soil-borne bacteria as a sulfur source, but application of sulfate through fertilization could affect this natural ...sulfur mobilizing process. This study investigates the effects of sulfate treatments on bacterial communities in semi-natural grasslands.
Agrostis stolonifera-dominated turfs with their autochthonous bacteria from Woburn Experimental Farm, UK, were incubated with and without additional sulfate over a period of eight weeks and compared to soil and rhizosphere samples taken from the field directly. Cultivable rhizobacteria able to desulfurize toluenesulfonate were dominated by strains affiliated to the
Variovorax,
Polaromonas and
Rhodococcus genera. The betaproteobacteria communities (16S rRNA gene-based denaturing gradient gel electrophoresis) and the desulfonating bacterial communities (
asfA based terminal restriction fragment length polymorphism) revealed clear differences between field rhizospheres and bulk soil and the two types of incubated rhizospheres. Clone libraries of
asfA from the sulfate-limited treatment were dominated by a new AsfA type, affiliated to
Polaromonas. The results from this study suggest that the community of desulfonating bacteria in the
Agrostis rhizosphere adapts quickly to changing levels of inorganic sulfate.
A cultivation‐independent approach based on polymerase chain reaction (PCR)‐amplified partial small subunit rRNA genes and genetic profiling by single‐strand conformation polymorphism (SSCP) was used ...to characterize the bacterial diversity inhabiting the rhizosphere of maize plants grown on an agricultural field. The community structures of two cultivars, a genetically engineered and a nonengineered variety, different herbicide regimes and soil tillage were compared with each other at two sampling dates. SSCP‐profiles were generated with DNA from bacterial cell consortia with primers hybridizing to evolutionarily highly conserved rRNA gene regions. On silver‐stained gels, each profile consisted of approx. 50 distinguishable bands. Similarity analyses of patterns recorded by digital image analyses could not detect any difference between cultivars or treatments that was greater than the variability between replicates. A total of 54 sequences recovered from different bands were identified and grouped into operational taxonomical units (OTUs). Surprisingly, only five of 40 OTUs contained sequences of both samplings. Three different bands from a profile were selected to test whether this small overlap was due to an incomplete recovery of sequences. From a faint band, two different OTUs were found when 12 clones were analysed, and from two strong bands 24 and 22 OTUs were detected from a total of 26 and 36 clones, respectively. The OTUs belonged to phylogenetically different groups of bacteria. Gene probes that were developed to target different bands of the profiles, however, indicated in Southern blot analyses that patterns between treatments, replicates and samplings, and even from two different growing seasons were highly conserved. Our study demonstrates that community profiles can consist of more sequences than detectable by staining and that gene probes in Southern blot can be a useful control to investigate the composition of microbial communities by genetic profiles.
Bacterial communities in rhizospheres of transgenic maize (
Zea mays, with the
pat-gene conferring resistance to the herbicide glufosinate; syn.
L-phosphinothricin) were compared to its isogenic, ...non-transgenic cultivar. Total DNA was extracted from bacterial cell consortia collected from rhizospheres of plants grown in an agricultural field. With the use of three different primer pairs binding to evolutionarily conserved regions of the bacterial 16S rRNA gene, partial sequences were amplified by polymerase chain reaction (PCR). The PCR products were subjected to single-strand conformation polymorphism (SSCP) to generate genetic profiles which corresponded to the diversity of the amplified sequences. Genetic profiles of rhizospheres consisted of 40–60 distinguishable bands depending on the chosen primer pairs, and the variability between independent replicates was very low. Neither the genetic modification nor the use of the herbicide Liberty (syn. Basta; active ingredient: glufosinate) affected the SSCP profiles as investigated with digital image analysis. In contrast, PCR–SSCP profiles of bacterial communities from rhizospheres of sugar beet, grown in the same field as a control crop, were clearly different. A less pronounced but significant difference was also observed with rhizosphere samples from fine roots of maize plants collected 35 and 70 days after sowing. Sequencing of the dominant 30 products from one typical SSCP profile generated from transgenic maize rhizospheres indicated the presence of typical soil and rhizosphere bacteria: half of the bands could be attributed to
Proteobacteria, mainly of the α- and β-subgroups. Other SSCP bands could be assigned to members of the following phylogenetic groups:
Cytophaga–
Flavobacterium–
Bacteroides,
Chlamydiales–
Verrucomicrobium,
Planctomyces,
Holophaga and to Gram-positive bacteria with a high G+C DNA content.
In this field study, we compared the bacterial communities inhabiting the rhizosphere of a transgenic, herbicide-resistant sugar beet (Beta vulgaris) cultivar with those of its nonengineered ...counterpart, using a genetic profiling technique based on PCR amplifications of partial 16S rRNA gene sequences and single-strand conformation polymorphism (SSCP). As a control for the plasticity of the bacterial community, we also analyzed the influence of herbicides, the field heterogeneity, and the annual variation. DNA was isolated from bacterial cell consortia that were directly collected from root material. PCR was carried out with primers that hybridized to evolutionarily conserved regions flanking variable regions 4 and 5 of the 16S rRNA gene. SSCP patterns of these PCR products were composed of approximately 50 distinguishable bands, as detected by silver staining of the gels after electrophoresis. Patterns of the replicates and the different treatments were highly similar, but digital image and similarity analyses revealed differences that corresponded to the positions of the replicates in the field. In addition, communities collected from sugar beet in two successive growing seasons could be distinguished. In contrast, no effect of the transgenic herbicide resistance was detectable. Sequencing of 24 dominant products of the SSCP profiles indicated the presence of bacteria from different phylogenetic groups, with Proteobacteria and members of the CytophagaFlavobacteriumBacteroides group being most abundant.Key words: genetic profiles, rRNA genes, transgenic sugar beet, risk assessment, rhizosphere, PCRSSCP, microbial community analysis, glufosinate, phosphinothricin.
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