Miranda Prendergast-Miller

Network analysis reveals that bacteria and fungi form modules that correlate independently with soil parameters

Network and multivariate statistical analyses were performed to determine interactions between bacterial and fungal community terminal restriction length polymorphisms as well as soil properties in paired woodland and pasture sites. Canonical correspondence analysis (CCA) revealed that shifts in woodland community composition correlated with soil dissolved organic carbon, while changes in pasture community composition correlated with moisture, nitrogen and phosphorus. Weighted correlation network analysis detected two distinct microbial modules per land use. Bacterial and fungal ribotypes did not group separately, rather all modules comprised of both bacterial and fungal ribotypes. Woodland modules had a similar fungal : bacterial ribotype ratio, while in the pasture, one module was fungal dominated. There was no correspondence between pasture and woodland modules in their ribotype composition. The modules had different relationships to soil variables, and these contrasts were not detected without the use of network analysis. This study demonstrated that fungi and bacteria, components of the soil microbial communities usually treated as separate functional groups as in a CCA approach, were co-correlated and formed distinct associations in these adjacent habitats. Understanding these distinct modular associations may shed more light on their niche space in the soil environment, and allow a more realistic description of soil microbial ecology and function.

Nitrous oxide production by the ectomycorrhizal fungi Paxillus involutus and Tylospora fibrillosa

Nitrous oxide (N(2)O) production by filamentous fungi has been demonstrated in pure culture and has been estimated indirectly in soils. However, it is unknown whether ectomycorrhizal fungi can also produce N(2)O. We demonstrate for the first time the ability of nitrogen (N)-tolerant ectomycorrhizal fungi (Paxillus involutus and Tylospora fibrillosa), found in forest soils under moderate to high rates of N deposition, to produce N(2)O from nitrate reduction. The N(2)O concentrations from the ectomycorrhizal fungal treatments after a 10-day pure culture experiment were 0.0117±0.00015 (P. involutus) and 0.0114±0.0003 (T. fibrillosa), and 0.0114±0.00043 μmol N(2)O L(-1) from a known fungal denitrifier (Fusarium lichenicola). No N(2)O was detected in the control treatment. Our results indicate the potential for these two N-tolerant ectomycorrhizal fungi to contribute to N(2)O production. Given that these species are abundant in many forest soils, the strength and regulation of fungal N(2)O production should now be verified in situ.

Biochar field testing in the UK: outcomes and implications for use

Background: There is a lack of biochar field trials in temperate climate regions. Wood biochar was applied during 2009–2011 to seven field experiments on five working farms in the UK, for arable, legume, horticultural and root crops. Results: Three trials showed no significant (p > 0.05) effect on crop yield, two showed positive effects of 5–6%, one showed a very strong increase of 100% and one showed a decrease of 2–16%. A meta-analysis of effect sizes was conducted for all treatments (n = 47), which showed a significant (p < 0.05) positive effect, increasing average yield by 0.4 t ha-1. Biochar application rates of 20 t ha-1 or under led to the greater benefits. Conclusion: This paper shows that, in some situations, biochar can bring benefits in modern temperate farming.

Plastic bag derived-microplastics as a vector for metal exposure in terrestrial invertebrates

Microplastics are widespread contaminants in terrestrial environments but comparatively little is known about interactions between microplastics and common terrestrial contaminants such as zinc (Zn). In adsorption experiments fragmented HDPE bags c. one mm2 in size showed similar sorption characteristics to soil. However, when present in combination with soil, concentrations of adsorbed Zn on a per mass basis were over an order of magnitude lower on microplastics. Desorption of the Zn was minimal from both microplastics and soil in synthetic soil solution (0.01 M CaCl2), but in synthetic earthworm guts desorption was higher from microplastics (40-60%) than soil (2-15%), suggesting microplastics could increase Zn bioavailability. Individual Lumbricus terrestris earthworms exposed for 28 days in mesocosms of 260 g moist soil containing 0.35 wt % of Zn-bearing microplastic (236-4505 mg kg-1) ingested the microplastics, but there was no evidence of Zn accumulation, mortality, or weight change. Digestion of the earthworms showed that they did not retain microplastics in their gut. These findings indicate that microplastics could act as vectors to increase metal exposure in earthworms, but that the associated risk is unlikely to be significant for essential metals such as Zn that are well regulated by metabolic processes.

C/N ratio drives soil actinobacterial cellobiohydrolase gene diversity.

ABSTRACT Cellulose accounts for approximately half of photosynthesis-fixed carbon; however, the ecology of its degradation in soil is still relatively poorly understood. The role of actinobacteria in cellulose degradation has not been extensively investigated despite their abundance in soil and known cellulose degradation capability. Here, the diversity and abundance of the actinobacterial glycoside hydrolase family 48 (cellobiohydrolase) gene in soils from three paired pasture-woodland sites were determined by using terminal restriction fragment length polymorphism (T-RFLP) analysis and clone libraries with gene-specific primers. For comparison, the diversity and abundance of general bacteria and fungi were also assessed. Phylogenetic analysis of the nucleotide sequences of 80 clones revealed significant new diversity of actinobacterial GH48 genes, and analysis of translated protein sequences showed that these enzymes are likely to represent functional cellobiohydrolases. The soil C/N ratio was the primary environmental driver of GH48 community compositions across sites and land uses, demonstrating the importance of substrate quality in their ecology. Furthermore, mid-infrared (MIR) spectrometry-predicted humic organic carbon was distinctly more important to GH48 diversity than to total bacterial and fungal diversity. This suggests a link between the actinobacterial GH48 community and soil organic carbon dynamics and highlights the potential importance of actinobacteria in the terrestrial carbon cycle.

Biochar, Tool for Climate Change Mitigation and Soil Management

Biochar is the solid remains of any organic material that has been heated to at least 350oC in a zero-oxygen or oxygen-limited environment, which is intended to be mixed with soils. If the solid remains are not suitable for addition to soils, or will be burned as a fuel or used as an aggregate in construction, it is defined as char not biochar. There is a very wide range of potential biochar feedstocks, e.g., wood waste, timber, agricultural residues and wastes (straws, bagasse, manure, husks, shells, fibers, etc.), leaves, food wastes, paper and sewage sludge, green waste, distiller’s grain, and many others. Pyrolysis is usually the technology of choice for producing biochar, though biomass gasification also produces smaller char yields. Syngas and pyrolytic bio-liquids, which have a potential use as energy carriers, are produced alongside biochar.

Earthworm-induced shifts in microbial diversity in soils with rare versus established invasive earthworm populations

European earthworms have colonised many parts of Australia, although their impact on soil microbial communities remains largely uncharacterised. An experiment was conducted to contrast the responses to Aporrectodea trapezoides introduction between soils from sites with established (Talmo, 64 A. trapezoides m-2) and rare (Glenrock, 0.6 A. trapezoides m-2) A. trapezoides populations. Our hypothesis was that earthworm introduction would lead to similar changes in bacterial communities in both soils. The effects of earthworm introduction (earthworm activity and cadaver decomposition) did not lead to a convergence of bacterial community composition between the two soils. However, in both soils, the Firmicutes decreased in abundance and a common set of bacteria responded positively to earthworms. The increase in the abundance of Flavobacterium, Chitinophagaceae, Rhodocyclaceae and Sphingobacteriales were consistent with previous studies. Evidence for possible soil resistance to earthworms was observed, with lower earthworm survival in Glenrock microcosms coinciding with A. trapezoides rarity in this site, lower soil organic matter and clay content and differences in the diversity and abundance of potential earthworm mutualist bacteria. These results suggest that while the impacts of earthworms vary between different soils, the consistent response of some bacteria may aid in predicting the impacts of earthworms on soil ecosystems.