Gut microbial communities and their potential roles in cellulose digestion and thermal adaptation of earthworms.

Adaptations to temperature and food resources, which can be affected by gut microbiota, are two main adaptive strategies allowing soil fauna to survive in their habitats, especially for cold-blooded animals. Earthworms are often referred to as ecosystem engineers because they make up the biggest component of the animal biomass found in the soil. They are considered as an important indicator in the triangle of soil quality, health and functions. However, the roles of gut microbiota in the environmental adaptation of earthworms at a large scale remain obscure. We explored the gut bacterial communities and their functions in the environmental adaptation of two widespread earthworm species (Eisenia nordenskioldi Eisen and Drawida ghilarovi Gates) in Northeast China (1661 km). Based on our findings, the alpha diversity of gut bacterial communities decreased with the increase of latitude, and the gut bacterial community composition was shaped by both mean annual temperature (MAT) and cellulose. Actinobacteria, Proteobacteria, Firmicutes, and Planctomycetes, recognized as the predominant cellulose degraders, were keystone taxa driving gut bacterial interactions. Actinobacteria, Firmicutes, and Planctomycetes were influenced by MAT and cellulose, and had higher contributions to gut total cellulase activity. The optimal temperature for total cellulase in the gut of E. nordenskioldi (25-30 °C) was lower than that of D ghilarovi (40 °C). The gut microbiota-deleted earthworms had the lowest cellulose degradation rate (1.07 %). The cellulose was degraded faster by gut bacteria from the host they were derived, indicating the presence of home field advantage of cellulose decomposition. This study provides a foundation for understanding the biotic strategies adopted by earthworms when they enter a new habitat, with gut microbiota being central to food digestion and environmental adaptability.

Two new species of Bimastos (Oligochaeta, Lumbricidae) from the Southern Appalachian Mountains, North America.

Two new species of Bimastos Moore are described based on morphological and molecular data. Bimastos nanae n. sp. resembles B. lawrenceae Fender, B. zeteki (Smith and Gittins) and B. welchi (Smith). Bimastos nanae n. sp. differs from these species in the position of the clitellum, size and number and position of thickened septa. Bimastos magnum n. sp. is similar to B. schwerti Csuzdi Chang and B. palustris Moore in having a fully annular clitellum and male pores on huge porophores. Bimastos magnum n. sp. differs from both species by having a more posterior position of the clitellum (in xxiv-xxxiii, xxxiv) and larger body size. With the description of these new species, the number of Bimastos species is raised to 14.

Global distribution of earthworm diversity.

Soil organisms, including earthworms, are a key component of terrestrial ecosystems. However, little is known about their diversity, their distribution, and the threats affecting them. We compiled a global dataset of sampled earthworm communities from 6928 sites in 57 countries as a basis for predicting patterns in earthworm diversity, abundance, and biomass. We found that local species richness and abundance typically peaked at higher latitudes, displaying patterns opposite to those observed in aboveground organisms. However, high species dissimilarity across tropical locations may cause diversity across the entirety of the tropics to be higher than elsewhere. Climate variables were found to be more important in shaping earthworm communities than soil properties or habitat cover. These findings suggest that climate change may have serious implications for earthworm communities and for the functions they provide.

Interactions among overstory structure, seedling life-history traits, and fire in frequently burned neotropical pine forests.

Fire-dependent pine forests in the Caribbean Basin cover extensive areas in the coastal plain of the Caribbean Sea and Gulf of Mexico and on several islands in the Bahamas Archipelago, Cuba, Hispaniola, and the Honduran Bay islands. These forests are high in conservation value but, unfortunately, remain mostly unprotected. Moreover, even though they are fire dependent, the use of fire for forest management often suffers from poor public perception and is prohibited by law in several countries. In this paper, we describe the fundamental links among fire, forest regeneration, and forest persistence in these ecosystems. We identify two general strategies based on the presence or absence of pine seedling adaptations for fire survival and describe management implications of these two strategies. We also introduce conceptual models describing fire, forest structure, and regeneration strategy linkages.

Observations on an epilobic Lumbricus rubellus (Oligochaeta, Lumbricidae) from the Great Smoky Mountains National Park, Tennessee, USA.

The genus Lumbricus L. was the first described genus of earthworms, with L. terrestris as its type species. The genus can be easily distinguished because it is the only lumbricid genus with a tanylobic prostomium, with the exception of the North American native Bimastos eiseni (Levinsen). With six known Lumbricus species introduced in North America (Reynolds Wetzel, 2012), Lumbricus rubellus is one of the most widespread. In addition, L. rubellus has been associated with negative ecological effects as result of its invasion (Greiner et al. 2012). The Great Smoky Mountains National Park in Tennessee and North Carolina, USA, is no exception from earthworm invasions (Snyder et al. 2011). Recent research in an area near the extreme southwestern end of the Park (35.5538º N; 83.9943º W), resulted in the collection of ten specimens of L. rubellus, on 27 July 2011. Among these specimens was one that had an abnormal epilobic prostomium and under-developed tubercula pubertatis, whereas the rest had the typical Lumbricus tanylobic prostomia and fully developed tubercula pubertatis. To facilitate discrimination and identification in future encounters of an epilobic L. rubellus we provide here a full description of this specimen. To our knowledge, this is the first reported case of a specimen of L. rubellus with an epilobic prostomium. The specimen will be deposited in the nascent Terrestrial Oligochaete Collection at the Georgia Museum of Natural History in Athens, Georgia, USA. The specimen was fixed in 10% formalin, and is preserved in 70% ethanol.

Effects of earthworm (Eisenia fetida) and wheat (Triticum aestivum) straw additions on selected properties of petroleum-contaminated soils.

Current bioremediation techniques for petroleum-contaminated soils are designed to remove contaminants as quickly and efficiently as possible, but not necessarily with postremediation soil biological quality as a primary objective. To test a simple postbioremediation technique, we added earthworms (Eisenia fetida) or wheat (Triticum aestivum) straw to petroleum land-farm soil and measured biological quality of the soil as responses in plant growth, soil respiration, and oil and grease (O&G) and total petroleum hydrocarbon (TPH) concentrations. Results indicated that plant growth was greater in earthworm-treated land-farm soil. Furthermore, addition of wheat straw resulted in greater total respiration in all soils tested (land-farm soil, noncontaminated reference soil, and a 1:1 mixture of land-farm and reference soils). We observed a 30% increase in soil respiration in straw-amended oily soil, whereas respiration increased by 246% in straw-amended reference soil. Much of the difference between oily and reference soils was attributable to higher basal respiration rates of nonamended oily soil compared to nonamended reference soil. Addition of earthworms resulted in greater total respiration of all soil and straw treatments except two (the land-farm and the 1:1 mixture soil treatments without straw). Straw and earthworm treatments did not affect O&G or TPH concentrations. Nevertheless, our findings that earthworm additions improved plant growth and that straw additions enhanced microbial activity in land-farm soil suggest that these treatments may be compatible with plant-based remediation techniques currently under evaluation in field trials, and could reduce the time required to restore soil ecosystem function.

Deep Ion Torrent sequencing identifies soil fungal community shifts after frequent prescribed fires in a southeastern US forest ecosystem.

Prescribed burning is a common management tool to control fuel loads, ground vegetation, and facilitate desirable game species. We evaluated soil fungal community responses to long-term prescribed fire treatments in a loblolly pine forest on the Piedmont of Georgia and utilized deep Internal Transcribed Spacer Region 1 (ITS1) amplicon sequencing afforded by the recent Ion Torrent Personal Genome Machine (PGM). These deep sequence data (19,000 + reads per sample after subsampling) indicate that frequent fires (3-year fire interval) shift soil fungus communities, whereas infrequent fires (6-year fire interval) permit system resetting to a state similar to that without prescribed fire. Furthermore, in nonmetric multidimensional scaling analyses, primarily ectomycorrhizal taxa were correlated with axes associated with long fire intervals, whereas soil saprobes tended to be correlated with the frequent fire recurrence. We conclude that (1) multiplexed Ion Torrent PGM analyses allow deep cost effective sequencing of fungal communities but may suffer from short read lengths and inconsistent sequence quality adjacent to the sequencing adaptor; (2) frequent prescribed fires elicit a shift in soil fungal communities; and (3) such shifts do not occur when fire intervals are longer. Our results emphasize the general responsiveness of these forests to management, and the importance of fire return intervals in meeting management objectives.