Increased Phenoloxidase Activity Research Articles

A Pattern Recognition Receptor C-type Lectin-S6 (CTL-S6) is Involved in the Immune Response in the Silkworm (Lepidoptera: Bombycidae).

Insect innate immunity is initiated by the special recognition and binding of the foreign pathogens, which is accomplished by the pattern recognition receptors (PRRs). As an important type of PRRs, C-type lectins (CTLs) play various roles in insect innate immunity, including pathogen recognition, stimulation of prophenoloxidase, regulation of cellular immunity and so on. In this study, we have cloned the full-length cDNA of a CTL gene named CTL-S6 from the silkworm, Bombyx mori. The open reading frame (ORF) of B. mori CTL-S6 encodes 378 amino acids, which contain a secretion signal peptide. The mRNA of CTL-S6 exhibited the highest transcriptional level in the midgut. Its transcriptional level increased dramatically in fat body and hemocytes upon Escherichia coli or Micrococcus luteus challenge. Purified recombinant CTL-S6 could bind to bacterial cell wall components, including peptidoglycan (PGN, from Bacillus subtilis) and lipopolysaccharide (LPS, from E. coli 0111:B4), and recombinant CTL-S6 was involved in the encapsulation and melanization of hemocytes. Furthermore, the addition of recombinant CTL-S6 to the hemolymph of silkworm resulted in a significant increase in phenoloxidase activity. Overall, our results indicated that B. mori CTL-S6 may serve as a PRR for the recognition of foreign pathogens, prophenoloxidase pathway stimulation and involvement in the innate immunity.

WITHDRAWN: Reduced fitness of the mosquito Culex pipiens (Diptera: Culicidae) after feeding on a blood meal with hepatitis C virus

Hepatitis C virus (HCV) is a blood-borne virus. Given that mosquitoes can take blood meals from healthy individuals as wells as HCV patients, we proved in a previous study that Culex pipiens can transmit HCV to human blood samples. In the present study, we aimed to test whether HCV in the blood meal can induce alterations in the biology of Cx. pipiens. To address this aim, Cx. pipiens females were fed HCV-positive fresh blood samples harvested from viremic HCV patients. The control mosquitoes were fed fresh HCV-free blood samples. Fragments of the HCV RNA negative strand were extracted from the mosquito bodies after 7 days of feeding, and RT-PCR sequenced to confirm the virus replication. In addition, several parameters that measure the fitness of the mosquitoes were observed. HCV acquired by the mosquitoes was able to replicate. Virus acquisition was associated with alterations in the architecture of the gut microvilli and the immune response, indicated by an increase in phenoloxidase activity. Interestingly, the mosquitoes that were fed the HCV-positive blood meal showed shorter median longevity (8 days) and laid fewer eggs than the control mosquitoes. Furthermore, the offspring of females fed the HCV-positive blood meal demonstrated a lower emergence rate than the controls. In sum, our results indicate that feeding on HCV by Cx. pipiens decreases fitness, which may, in turn, affect potential as a vector.

Pectin of cacao pod husk, an efficient immunostimulant for white shrimp, Litopenaeus vannamei

The disposal of cacao pod husk, a byproduct of cacao bean processing, can cause serious adverse environmental impacts, motivating scientist to explore and develop potential beneficial applications of this resource. Dried cacao pod husk was extracted with ethanol to obtain a 10.6% pectin of cacao pod husks (pCPH), and its effects on the immunocompetence of Litopenaeus vannamei were estimated. Measured variables included total haemocyte count, differential haemocyte count, phenoloxidase activity, respiratory bursts, as well as phagocytic activity and clearance efficiency against Vibrio alginolyticus after receiving pCPH at 0, 1.5, 3, and 6 μg shrimp−1 for 0, 1, 3 and 7 days via injection, and their resistance to thermal stress and V. alginolyticus infection were further evaluated. No significant differences were observed in total haemocyte count, differential haemocyte count, and respiratory bursts in shrimp receiving pCPH at 1.5 μg shrimp−1 for 1 day; however, these variables were significantly elevated after 3 days of injection, compared to the control group. The significantly increased phenoloxidase activity was assessed in shrimp receiving pCPH at 1.5, 3 and 6 μg shrimp−1 within 3 days, and activity returned to the baseline after 7 days. Furthermore, the reduced phenoloxidase activity per granulocytes or respiratory bursts per haemocytes maintained homeostasis following the variation of haemogram. For gene expression assessments in haemocytes, the immune-related genes of the lipopolysaccharide and β-1,3-glucan binding protein, prophenoloxidase II and anti-lipopolysaccharide factor as well as innate immune signaling pathway-related genes of toll-like receptors 1 and 3 significantly increased after shrimp received pCPH for 1 day. The increases in phagocytic activity and clearance efficiency were only detected in shrimp receiving pCPH at 6 μg shrimp−1 within 7 days, compared to the control. There was no significant difference in the mortality ratio of shrimp against hyperthermal stress when they received pCPH for 1 day, and the significant higher resistance to hypothermal stress and V. alginolyticus infection were found in shrimp received pCPH at 6 μg shrimp−1 for 1 days than those in the other treatments. It is therefore found that pCPH triggers immune responses serving as an immunostimulant capable of enhancing resistance against V. alginolyticus and hypothermal stress.

Activation of prophenoloxidase and hyperglycemia as indicators of microbial stress in the blue swimmer crab Portunus pelagicus

Portunus pelagicus is exposed to different kinds of microorganisms leading to high metabolic stress that affects its life. The present study evaluates the activity of Phenoloxidase (PO), which is an enzyme that is actively involved in the activation of the immune defense system and hyperglycemia in P. pelagicus challenged with Escherichia coli and Vibrio harveyi injections. The results revealed a major impact of microbial injection on PO activity and significant variations in hemolymph glucose and CHH levels. Reduction of glucose level was observed after 24 h microbial incubation (275.26 ± 28.85 and 175.23 ± 21.70 μg/ml in V. harveyi and E. coli injected crabs, respectively). An elevated level of CHH (13.54 ± 0.55 fmol/ml) was observed in V. harveyi-injected crabs, and increased PO activity was recorded in E. coli-injected crabs. The results of the present study indicate that microbial stress leads to the activation of the defense system and hyperglycemia in P. pelagicus.

A new bacteria-free strategy induced by MaGal2 facilitates pinewood nematode escape immune response from its vector beetle.

Symbiotic microbes play a crucial role in regulating parasite-host interactions; however, the role of bacterial associates in parasite-host interactions requires elucidation. In this study, we showed that, instead of introducing numerous symbiotic bacteria, dispersal of 4th-stage juvenile (JIV ) pinewood nematodes (PWNs), Bursaphelenchus xylophilus, only introduced few bacteria to its vector beetle, Monochamus alternatus (Ma). JIV showed weak binding ability to five dominant bacteria species isolated from the beetles' pupal chamber. This was especially the case for binding to the opportunistic pathogenic species Serratia marcescens; the nematodes' bacteria binding ability at this critical stage when it infiltrates Ma for dispersal was much weaker compared with Caenorhabditis elegans, Diplogasteroides asiaticus, and propagative-stage PWN. The associated bacterium S. marcescens, which was isolated from the beetles' pupal chambers, was unfavorable to Ma, because it caused a higher mortality rate upon injection into tracheae. In addition, S. marcescens in the tracheae caused more immune effector disorders compared with PWN alone. Ma_Galectin2 (MaGal2), a pattern-recognition receptor, was up-regulated following PWN loading. Recombinant MaGal2 protein formed aggregates with five dominant associated bacteria in vitro. Moreover, MaGal2 knockdown beetles had up-regulated prophenoloxidase gene expression, increased phenoloxidase activity, and decreased PWN loading. Our study revealed a previously unknown strategy for immune evasion of this plant pathogen inside its vector, and provides novel insights into the role of bacteria in parasite-host interactions.

Impact of Dopamine and Hydrogen Peroxide on Physiological Stress Parameters of Sarcophaga surcoufi (Diptera: Sarcophagidae)

Natural phenolics and reactive oxygen chemical species can have metabolic and fitness costs in insects and thus represent potential insecticidal agents. The response levels of total protein, phenoloxidase, proteases, chitinases, and total antioxidant activities to dopamine and hydrogen peroxide (H2O2) injected into third-instar flesh fly, Sarcophaga surcoufi Villeneuve (Diptera: Sarcophagidae), larvae were measured. In comparison to control groups, total protein initially increased following treatment with H2O2, but decreased at later sampling intervals. Treatment with dopamine did not affect total protein or protease activity for up to 12 h after treatment, but a slight decrease was observed in both at 24 and 36 h after treatment. Treatment with H2O2 decreased protease activity at all sampling intervals. H2O2 treatment increased phenoloxidase activity at each sampling interval, while treatment with dopamine decreased the activity at each interval. Total antioxidant activity increased substantially 12 h after treatment with H2O2 and increased only slightly 24 h after treatment before decreasing at 36 h, while dopamine increased antioxidant activity at all sampling intervals. Chitinase activity increased 12 h after H2O2 treatment, but then decreased at 24 and 36 h, but dopamine had no effect on chitinase activity. Antioxidants, phenoloxidase, and chitinase are important metabolic defense components in insects, and increases or decreases in each impacts the physiological integrity of the insect exposed to stressors that increase or decrease their quantity and activity.

Heat stress during development affects immunocompetence in workers, queens and drones of Africanized honey bees (Apis mellifera L.) (Hymenoptera: Apidae).

Though social insects generally seem to have a reduced individual immunoresponse compared to solitary species, the impact of heat stress on that response has not been studied. In the honey bee, the effect of heat stress on reproductives (queens and males/drones) may also vary compared to workers, but this is currently unknown. Here, we quantified the activity of an enzyme linked to the immune response in insects and known to be affected by heat stress in solitary species: phenoloxidase (PO), in workers, queens and drones of Africanized honey bees (AHBs) experimentally subjected to elevated temperatures during the pupal stage. Additionally, we evaluated this marker in individuals experimentally infected with the entomopathogenic fungus Metarhizium anisopliae. Differences in PO activity were found between sexes and castes, with PO activity generally higher in workers and lower in reproductives. Such differences are associated with the likelihood of exposure to infection and the role of different individuals in the colony. Contrary to our expectation, heat stress did not cause an increase in PO activity equally in all classes of individual. Heat stress during the pupal stage significantly decreased the PO activity of AHB queens, but not that of workers or drones, which more frequently engage in extranidal activity. Experimental infection with Metarhizium anisopliae reduced PO activity in queens and workers, but increased it in drones. Notably, heat stressed workers lived significantly shorter after infection despite exhibiting greater PO activity than queens or drones. We suggest that this discrepancy may be related to trade-offs among immune response cascades in honey bees such as between heat shock proteins and defensin peptides used in microbial defence. Our results provide evidence for complex relationships among humoral immune responses in AHBs and suggest that heat stress could result in a reduced life expectancy of individuals.

Short-term Response in Molecular and Biochemical Adaptation of White Shrimp (Litopenaeus vannamei) Postlarvae Reared in A Biofloc System

Up regulation of heat shock proteins (HSPs) in organisms can be detected in response to many kinds of stressor. Recently there were few studies have focused on the three kinds of heat shock proteins (HSPs) and antioxidant enzyme activity after biofloc stress. The objective of this study was to investigate the effect of different biofloc volume on the expressions of (LvHSP60, LvHSP70, and LvHSP90), the activity of superoxide dismutase (SOD) and phenoloxidase (PO) of the L. vannamei after biofloc addition. PL10 L. vannamei were divided into three groups: precondition, biofloc stress (5mL/L, 10mL/L, 15mL/L), and recovery. The gene expression results showed that the expressional levels of LvHSP60, LvHSP70, and LvHSP90 were increased significantly in 6h treatment and tend return to normal conditions after 48h treatment. Superoxide dismutase activity was reduced during treatment and phenoloxidase activity was elevated slightly after 12h to 24h and tend to pretreatment level at recovery periods. All of these HSPs expression reverted to normal levels 6h after the recovery period. The results indicated that different expression patterns of the three HSPs. HSP60 have a longer and higher protection expression after 12h treatment than HSP70 and HSP90. HSP90 was more sensitive in 6h at all treatments than HSP60 and HSP70. It is concluded that supplementation of biofloc with the volume of 5-15mL/L caused Hsp protection in L. vannamei PLs at the first 6h to 48h treatment and increased phenoloxidase activity at 24-48h treatment and reduced survival rate of the white shrimp.

Bmserpin2 Is Involved in BmNPV Infection by Suppressing Melanization in Bombyx mori.

Melanization, an important defense response, plays a vital role in arthropod immunity. It is mediated by serine proteases (SPs) that convert the inactive prophenoloxidase (PPO) to active phenoloxidase (PO) and is tightly regulated by serine protease inhibitors (serpins) which belong to a well distributed superfamily in invertebrates, participating in immune mechanisms and other important physiological processes. Here, we investigated the Bmserpin2 gene which was identified from a transcriptome database in response to Bombyx mori nucleopolyhedrovirus (BmNPV) infection. Quantitative real-time polymerase chain reaction (qRT-PCR) results showed that Bmserpin2 was expressed in all tissues, with maximum expression in fat body. Upon BmNPV infection, the expression of Bmserpin2 was up-regulated in P50 (susceptible strain) and BC9 (resistant strain) in haemocytes, fat body and the midgut. However, up-regulation was delayed in BC9 (48 or 72 h), in contrast to P50 (24 h), after BmNPV infection. Meanwhile, Bmserpin2 could delay or inhibit melanization in silkworm haemolymph. Significant increased PO activity can be observed in Bmserpin2-depleted haemolymph under NPV infection. Furthermore, the viral genomic DNA copy number was decreased in Bmserpin2-depleted haemolymph. We conclude that Bmserpin2 is an inducible gene which might be involved in the regulation of PPO activation and suppressed melanization, and have a potential role in the innate immune system of B. mori.

Toxicity and Oxidative Stress Induced in Spodoptera littoralis (Boisduval) (Lepidoptera: Noctuidae) Treated with Some Insecticides

Integrated pest management of herbivorous pests relies on combining bio-insecticides and chemical insecticides for a satisfactory population control. The present study focused on evaluating the comparative toxicity of five insecticides, with different modes of action, against third and fifth instar larvae of Spodoptera littoralis and their influence on extent of oxidative stress in insect via detecting vitamin C content as well as measuring the activity of phenol oxidase (PO), catalase (CAT), peroxidase (POX), glutathione-S-transferase (GST) antioxidant enzymes compared to control. The results revealed that emamectin benzoate and indoxacarb were the most potent insecticides among the selected insecticides, based on their respective LC50 values. Thiacloprid, indoxacarb and emamectin benzoate significantly reduced Vitamin C content. Almost all treatments significantly increased PO activity. Only emamectin benzoate and Bacillus thuringiensis significantly induced POX activity. Indoxacarb and emamectin benzoate increased CAT activity in both instar larvae, whereas thiacloprid and indoxacarb decreased GST activity. In conclusion, emamectin benzoate and indoxacarb were the most potent insecticides. Activity of oxidative stress biomarkers upon insecticidal pressure has showed variable response.

The insect, Galleria mellonella, is a compatible model for evaluating the toxicology of okadaic acid

The polyether toxin, okadaic acid, causes diarrhetic shellfish poisoning in humans. Despite extensive research into its cellular targets using rodent models, we know little about its putative effect(s) on innate immunity. We inoculated larvae of the greater wax moth, Galleria mellonella, with physiologically relevant doses of okadaic acid by direct injection into the haemocoel (body cavity) and/or gavage (force-feeding). We monitored larval survival and employed a range of cellular and biochemical assays to assess the potential harmful effects of okadaic acid. Okadaic acid at concentrations ≥ 75 ng/larva (≥ 242 μg/kg) led to significant reductions in larval survival (> 65%) and circulating haemocyte (blood cell) numbers (> 50%) within 24 h post-inoculation. In the haemolymph, okadaic acid reduced haemocyte viability and increased phenoloxidase activities. In the midgut, okadaic acid induced oxidative damage as determined by increases in superoxide dismutase activity and levels of malondialdehyde (i.e. lipid peroxidation). Our observations of insect larvae correspond broadly to data published using rodent models of shellfish-poisoning toxidrome, including complementary LD50 values: 206–242 μg/kg in mice, ~ 239 μg/kg in G. mellonella. These data support the use of this insect as a surrogate model for the investigation of marine toxins, which offers distinct ethical and financial incentives.

Multiple-strain probiotics appear to be more effective in improving the growth performance and health status of white shrimp, Litopenaeus vannamei, than single probiotic strains

The probiotic efficiencies of the mixed probiotics containing Lactobacillus pentosus BD6, Lac. fermentum LW2, Bacillus subtilis E20, and Saccharomyces cerevisiae P13 for shrimp growth and health status improvement were better than those when using single probiotics. The probiotic mixture at a level of 108 colony-forming units (cfu) (kg diet)−1 and the diets containing BD6 and E20 at 109 cfu (kg diet)−1 significantly improved the growth and health status of shrimp, whereas the diets containing P13 or LW2 did not significantly affect the growth of shrimp. No significant difference in the carcass composition was recorded among the control and treatments. After 56 days of feeding, shrimp fed the diet containing the probiotic mixture (107∼109 cfu (kg diet)−1) had higher survival after injection with the V. alginolyticus, but 109 cfu (kg diet)−1 of single probiotics (except for S. cerevisiae P13) had to be administered to improve shrimp survival. The better disease resistance of shrimp in groups fed the probiotic mixture might have been due to increased phenoloxidase activity, respiratory bursts, and lysozyme activity of hemocytes. Therefore, we considered that the probiotic mixture could adequately provide probiotic efficiency for white shrimp, and a diet containing 108 cfu (kg diet)−1 probiotic mixture is recommended.

Maintenance of redox balance by antioxidants in hemolymph of the greater wax moth Galleria mellonella larvae during encapsulation response.

The lipid peroxidation process in hemocytes, activities of phenoloxidase and key enzymatic antioxidants (superoxide dismutase, glutathione-S-transferase, catalase) and nonenzymatic antioxidants (thiols, ascorbate) in hemolymph of the greater wax moth Galleria mellonella L. (Lepidoptera: Pyralidae) were studied during the encapsulation process of nylon implants. It has been established that as soon as 15min after piercing a cuticle with the implant, a capsule is formed on its surface. Active melanization of the capsule has been shown to last for 4 h. During the first hours after incorporating the implant, an increase in phenoloxidase activity and lipid peroxidation in the insect hemocytes has been revealed. Adhesion and degranulation on the surface of foreign object lead to the depletion of total hemocytes count (THC). Our results indicated that thiols and ascorbate molecules take part in the immediate antioxidant response, during later stages of encapsulation process hemolymph glutathione-S-transferase detoxifies and protects insect organism thereby restoring the internal redox balance. We suggest that nonenzymatic and enzymatic antioxidants of hemolymph plasma play a key role in the maintenance of redox balance during encapsulation of foreign targets.

Endosymbiont-based immunity in Drosophila melanogaster against parasitic nematode infection.

Associations between endosymbiotic bacteria and their hosts represent a complex ecosystem within organisms ranging from humans to protozoa. Drosophila species are known to naturally harbor Wolbachia and Spiroplasma endosymbionts, which play a protective role against certain microbial infections. Here, we investigated whether the presence or absence of endosymbionts affects the immune response of Drosophila melanogaster larvae to infection by Steinernema carpocapsae nematodes carrying or lacking their mutualistic Gram-negative bacteria Xenorhabdus nematophila (symbiotic or axenic nematodes, respectively). We find that the presence of Wolbachia alone or together with Spiroplasma promotes the survival of larvae in response to infection with S. carpocapsae symbiotic nematodes, but not against axenic nematodes. We also find that Wolbachia numbers are reduced in Spiroplasma-free larvae infected with axenic compared to symbiotic nematodes, and they are also reduced in Spiroplasma-containing compared to Spiroplasma-free larvae infected with axenic nematodes. We further show that S. carpocapsae axenic nematode infection induces the Toll pathway in the absence of Wolbachia, and that symbiotic nematode infection leads to increased phenoloxidase activity in D. melanogaster larvae devoid of endosymbionts. Finally, infection with either type of nematode alters the metabolic status and the fat body lipid droplet size in D. melanogaster larvae containing only Wolbachia or both endosymbionts. Our results suggest an interaction between Wolbachia endosymbionts with the immune response of D. melanogaster against infection with the entomopathogenic nematodes S. carpocapsae. Results from this study indicate a complex interplay between insect hosts, endosymbiotic microbes and pathogenic organisms.

Altered immunity in crowded Mythimna separata is mediated by octopamine and dopamine

Similar to pathogenic infection, high population density alters insects’ prophylactic immunity. Density-dependent prophylaxis has been reported in many polyphenic insects, but the regulatory mechanism underlying this phenomenon remains unclear. The biogenic monoamines are known to play critical roles in mediating insect immune responses. In the current study, the immune capacity and the levels of three biogenic monoamines were investigated in the polyphenic larvae of Mythimna separata, reared at the densities of 1, 2, 5, 10, and 30 larvae per 650-mL jar. Concomitant with the increased phenoloxidase (PO) activity and total haemocyte count in the larvae at high densities (5, 10, 30 larvae/jar), the octopamine level was also increased. In contrast, the dopamine level was decreased, and the 5-hydroxytryptamine level was not significantly affected. Injection of octopamine induced significant increases in the total haemocyte count and PO activity. Conversely, epinastine, a specific antagonist of octopamine, decreased the total haemocyte count and PO activity. Another octopamine antagonist, phentolamine, inhibited the activity of PO and lysozymes. In addition, injection of dopamine induced a significant increase in PO activity and decreased the total haemocyte count and lysozyme activity. These results suggested that both octopamine and dopamine mediate the increases in total haemocyte count and PO activity in the crowded larvae.

Effects of Different Land Types on Soil Enzyme Activity in the Qinghai Lake Region

This study sought to investigate the influence of different land types on soil enzyme activities and identify the driving factors behind it. Three prevalent land cover types and one land use type by Qinghai Lake were selected (original wetland, natural grassland, recovered shrubland, and farmland), and the surface soil at a depth of 0–10 cm was collected for analysis. The results indicated that soil organic carbon, active carbon, dissolved organic carbon, total nitrogen content, microbial biomass, and soil hydrolase activity decreased, whereas phenol oxidase activity increased after converting the wetland into other land types. However, the differences in microbial biomass and enzyme activities between farmland and recovered shrubland were not significant. Similar trends in β-glucosidase and cellobiohydrolase activities were detected and these were more sensitive to the changes in land types. Soil carbon and nitrogen contents were shown to be responsible for the variability in hydrolase activity, with active carbon showing the strongest influence. Wetland conversion induces the loss of soil carbon and nitrogen stock, which may further decrease the availability of organic matter for microbes. A decrease in hydrolase activity and an increase in phenol oxidase activity may indicate shifts in organic carbon bioavailability after wetland conversion.

Physical Conditions Regulate the Fungal to Bacterial Ratios of a Tropical Suspended Soil

As a source of ‘suspended soils’, epiphytes contribute large amounts of organic matter to the canopy of tropical rain forests. Microbes associated with epiphytes are responsible for much of the nutrient cycling taking place in rain forest canopies. However, soils suspended far above the ground in living organisms differ from soil on the forest floor, and traditional predictors of soil microbial community composition and functioning (nutrient availability and the activity of soil organisms) are likely to be less important. We conducted an experiment in the rain forest biome at the Eden Project in the U.K. to explore how biotic and abiotic conditions determine microbial community composition and functioning in a suspended soil. To simulate their natural epiphytic lifestyle, bird’s nest ferns (Asplenium nidus) were placed on a custom-built canopy platform suspended 8 m above the ground. Ammonium nitrate and earthworm treatments were applied to ferns in a factorial design. Extracellular enzyme activity and Phospholipid Fatty Acid (PLFA) profiles were determined at zero, three and six months. We observed no significant differences in either enzyme activity or PLFA profiles between any of the treatments. Instead, we observed decreases in β-glucosidase and N-acetyl-glucosaminidase activity, and an increase in phenol oxidase activity across all treatments and controls over time. An increase in the relative abundance of fungi during the experiment meant that the microbial communities in the Eden Project ferns after six months were comparable with ferns sampled from primary tropical rain forest in Borneo.

Age, sex, mating status, but not social isolation interact to shape basal immunity in a group-living insect

Immunity is a crucial but costly trait. Individuals should therefore adjust their investment into immunity to their condition and infection risks, which are often determined by their age, sex, mating status and social environment. However, whether and how these four key factors can interact to shape basal immunity remains poorly understood. Here, we tested the simultaneous effects of these factors on hemocyte concentration and phenoloxidase activity in adults of the European earwig. We found that hemocyte concentration increased with age, and that this increase was stronger in males. We also found an age-dependent increase in phenoloxidase activity in males and virgin females, but not in mated females. However, the two immune parameters were independent of social isolation. Overall, our results reveal that a complex interplay between age, sex and mating status determines basal immunity and stress the importance of interactions in our understanding of immune investment.

Gasification biochar has limited effects on functional and structural diversity of soil microbial communities in a temperate agroecosystem

Biochar may enhance soil fertility and carbon (C) sequestration but there is still a lack of comprehensive understanding of its effects on soil microbial communities and functioning. This study tested the differential effects of two doses (6–8 and 0.8–1.4 t ha−1 for High and Low doses, respectively) of wheat straw gasification biochar (GBC) and fresh straw incorporated as soil amendments into an agricultural field in Denmark. Soils were analysed three months after the amendments for pH, total organic matter, microbial biomass (ATP), ten enzymatic activities, catabolic potential by substrate-induced respiration (MicroResp™), soil toxicity test (BioTox™) and bacterial community structure (Illumina 16S rRNA gene sequencing). No significant effect of biochar treatment was observed regarding ATP content, catabolic community profiles and soil toxicity. The higher dose of GBC increased phenol oxidase activity and soil pH, and decreased the cellulase activity. No major effect of high dose GBC was observed on the soil community diversity, and only minor effect on the community composition, with an increase in the relative abundance of a single OTU associated with Acidobacteria_Gp16. Addition of low dose of GBC caused an increase in the relative abundance of the rare members in the microbial communities thus increasing the diversity of soil microorganisms. A comparable effect was observed with the addition of fresh straw. Overall, our results indicated that GBC as soil amendment had a limited effect on the functional and structural diversity of soil microbial communities in a Danish temperate agroecosystem.

Small changes in water levels and groundwater nutrients alter nitrogen and carbon processing in dune slack soils

Dune slacks are biodiverse seasonal wetlands which experience considerable fluctuation in water table depth. They are under threat from eutrophication and lowered water tables due to climate change and water abstraction. The biological effects caused by the interactions of these pressures are poorly understood, particularly on soil processes. We used a mesocosm experiment and laboratory assays to study the impact of lowered water tables, groundwater nitrogen contamination, and their synergistic effects on soil microbial processes and greenhouse gas emissions. This study showed that just a 10 cm decrease in water table depth led to a reduction in denitrification and to a corresponding increase in soil nitrogen content. Meanwhile N2O emissions occurred for longer durations within dune slack soils subject to higher concentrations of groundwater nitrogen contamination. The results from extracellular enzyme assays suggest that decomposition rates increase within drier soils shown by the increase in β-glucosidase activity, with further sensitivity to groundwater nitrogen contamination shown by the increase in phenol oxidase activity. Dune slack soils with a 10 cm lower water table had significantly lower CH4 emissions, nearly 5 times lower in the drier soils. Our findings demonstrate that dune slacks are sensitive to both small changes in groundwater levels and to groundwater nitrogen contamination. The biological impacts from lowered water tables are likely to be intensified where there is also groundwater nitrogen contamination.