Naturally occurring stable isotopes, such as carbon-13 and nitrogen-15, can be used for identifying their sources, as tracers, or in mass balance estimation. These isotopes have been widely used in studying food habit, ecological niche, food web, and nutrient cycles. Following the development of mixing models and the concept of isotopic niche, stable isotopes have become one of the most important approaches in studying the soil food web and C and N biogeochemistry. In addition to using the natural abundance of stable isotopes, leaf litter artificially enriched in carbon-13 and nitrogen-15 provides strong signals that allow us to follow the C and N from leaf litter into soil organic matter, tissues of soil fauna, microbial community, and, carbon dioxide and nitrous oxide emitted from soil. By combining these state-of-the-art approaches, we are currently addressing research questions focusing on competition, niche shift, functional groups, C sequestration, and soil respiration.
Primary collaborator: Katalin Szlavecz (Johns Hopkins University) |
Earthworms can affect soil microbes through changing resource availability by consuming leaf litter and soil organic matter, by casting, and by vertical translocation of carbon and nitrogen in the soil. Earthworm burrows, casts and middens, also known as the "drilosphere", is rich in soluble C and earthworm mucus when fresh, and is generally considered a hotspot of microbial activities. Bacteria are known to be an important part of earthworm nutrition. Earthworms may selectively feed on bacteria or bacteria-colonized patches. In addition, earthworm might host a distinct gut microbiome, and passing through earthworm gut might lead to selection for specific microbial groups. Thus, the presence of earthworms, or even different species of earthworms, may have fundamental influence on soil microbiota. We are currently using 16S metagenomics coupled with next-generation sequencing (Illumina MiSeq platform) to investigate the complex interactions between earthworms and soil microbiota.
Primary collaborator: Shan-Hua Yang (楊姍樺; National Taiwan University) |
Pontoscolex corethrurus is an invasive earthworm originally from Brazil. It has become one of the most common species in the tropical and subtropical regions worldwide, and is also quite often the dominant species in urban green space and the satoyama landscapes in Taiwan. We are examining potential invasional meltdown, where two invasive species form a loop of positive feedback, between P. corethrurus and invasive plants, and how the complex interactions between the two invaders, other soil fauna, and microbes affect invasion success, the community structures of soil organisms, and soil C and N dynamics under different land uses and managements.
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Soil is dubbed "the poor man's tropical rainforest". It is the habitat for a diverse group of organisms, from earthworms and isopods to tiny, microscopic animals, such as pseudoscorpions, springtails, mites and nematodes. A square meter of soil in a forest is home to hundreds of species of invertebrates, and in that same area, we can often find a couple of hundred individuals of earthworms, tens of thousands of springtails, and several million nematodes. However, a lot of this diversity has remained unknown to human beings. Take nematodes for example. There are only about 20 thousand described species of nematodes in the world, and that is less than 2% of the estimated diversity. Soil mesofauna are invertebrates with a body size between 0.1mm and 2mm. They generally live in the leaf litter layer and/or surface soil. In general, this group includes pseudoscorpions (Pseudoscorpiones), springtails (Collembola), mites (Acari), proturans (Protura), pauropods (Pauropoda), tardigrades (Tardigrada), enchytraeids (Enchytraeidae) and nematodes (Nematoda). Mocroarthropod mesofauna, such as pseudoscorpions, mites, and springtails, can be extracted using Berlese funnel, an apparatus that drives the animals moving downwards into a collecting container by creating a vertical moisture gradient. We are currently looking into the diversity of Pseudoscorpiones and Collembola in Taiwan, and are seeking students and collaborators who are interested in any groups of soil mesofauna to join us.
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Collembola (Springtails)Collembola, commonly known as springtails, is a group of six-legged arthropods closely related to insects. No more than a few millimeters long, these creatures are microscopic. They are abundant in moist terrestrial environment, especially leaf litter and soil. Springtails vary dramatically in color and body shape; some are quite colorful. These adorable animals are detritivores and consumers, feeding on fungi, plant residues, and perhaps other soil animals. Most springtails have a tail-like structure called furcula, which, when not in use, is folded under the body. When furcula is released, it flings the animal into the air within a fraction of a second. This behavior serves as a way to rapidly move or evade danger, and gives the microarthropod the name "springtail".There are about 3,600 species of springtails worldwide. In Taiwan, 26 species belonging to 20 genera and eight families have been documented in the literature. However, these numbers are based on an 40-year-old paper published in 1981, and obviously are long overdue for an update.
See more photos at Hsin-Ju Cheng's Flickr: https://flic.kr/ps/3UjMUB |
PseudoscorpionsPseudoscorpions are microscopic arthropods closely related to spiders and scorpions. These tiny creatures can be found under tree barks and rocks, in the leaf litter and soil, and sometimes on the exoskeleton of insects. Most pseudoscorpions need moist environment, but some species in the families Olipiidae and Cheliferidae are adapted to dry conditions and can even be found in the desert. Two genera in particular, Garypus of the family Garypidae and Nipponogarypus of the family Olipiidae, are restricted to seashore habitats in the subtropical and tropical regions. As of 2020, there are c.a. 3,385 species of pseudoscorpions with 26 families in the world. In Taiwan, 10 species belonging to eight genera and eight families have been documented. However, the real species richness of pseudoscorpions is likely much higher, as only a few scientific studies have focused on these adorable tiny animals. Pseudoscorpions are formidable predators, feeding on springtails (Collembola) and other microarthropods for food. They immobilize their preys by ejecting venom from their padipalp (the pair of big, claw-like structures). Some pseudoscorpion species are known to be phoretic. Their dispersal may be facilitated by hitchhiking on insects or small mammals, the reason why we can sometimes find them on insects. In Taiwan, one pseudoscorpion species, Lophochernes bicarinatus, is known to be phoretic, hitchhiking on the longhorn beetle Batocera davidis.
Primary collaborator: Hsiang-Yun Lin (林湘芸; National Taiwan Normal University) |
This project is a part of several researchers’ efforts to understand earthworm diversity in Taiwan. In 2015, it reached a milestone by adding the 100th described species into the list of Taiwan’s earthworm fauna, up from 26 in 1995. However, an estimated number of at least another 100 species is still waiting to be discovered and described. Most native earthworms in Taiwan belong to the Pheretima complex, a group with arguably the most active earthworm taxonomist community in the world. The Pheretima complex contains about 1000 described species within 12 widely-accepted genera that are indigenous to Australia, Southeast Asia, and the eastern part of East Asia. The rapidly increasing number in the list of species, both nationally and globally, makes species delimitation more and more challenging, and is calling for an integrated taxonomic approach that combines morphology, DNA barcoding, and, in some cases, molecular phylogeny. Morphology is still, and will always remain, the centerpiece of earthworm taxonomy, but the contributions from DNA barcoding, phylogeny, and biogeography improve our understanding on morphological variations within a species and help species delimitation.
Primary collaborator: Huei-Ping Shen (沈慧萍; Endemic Species Research Institute); Csaba Csuzdi (Eszterházy Károly University) |
The study of earthworm diversity and evolution have seen a lot of progress since DNA was used for the first time in 2005 to facilitate taxonomic revision and address biogeographic questions in earthworms. However, many important questions still remain unanswered, from the concepts of the families or subfamilies Acanthodrilidae, Megascolecidae, Exxidae, Diplocardiinae, Benhamiinae, etc., to the systematics of the families Lumbricidae and Megascolecidae. In East and Southeast Asia, the earthworm fauna is dominated by the Pheretima complex, also known as the pheretimoids or the pjeretimoid earthworms, of Megascolecidae. This species-rich group is currently the home of roughly 1,000 described species and 12 widely-accepted genera. However, the genus-level systematics of this group is in chaos, with many polyphyletic genera, such as Amynthas, Metaphire, Pithemera, Polypheretima and Pheretima, defined by plesiomorphic and/or homoplasic characters. At the within-genus level, earthworm taxonomists and ecologists frequently face questions regarding potential synonyms, intraspecific morphological and genetic variations, biogeography of closely related species, species delimitation within species complexes, and cryptic species. These unresolved questions not only hinders our understanding on earthworm biodiversity, but also slows us down regarding understanding how earthworm communities affect ecosystem functions. In the past, we investigated topics focusing on the Metaphire formosae species group (Megascolecidae), the Amynthas wulinensis species complex (Megascolecidae), the Aporrectodea caliginosa species complex (Lumbricidae), and the genera Bimastos, Dendrodrilus, Allolobophoridella, Eisenoides, Healyella and Spermophorodrilus (Lumbricidae). Currently, we are focusing on the genus Drawida (Moniligastridae) and the 12 genera within the Pheretima complex (Megascolecidae), and, while studying their phylogenetics, systematics and taxonomy, use these groups as models to understand earthworm evolution and speciation.
Primary collaborator: Huei-Ping Shen (沈慧萍; Endemic Species Research Institute) |
Earthworm communities at local scales are usually composed of fewer than a dozen species, but yet the factors determining their community structures are poorly understood. We investigate how abiotic environmental factors and earthworm interspecific interactions determine the community structures of earthworms in temperate and subtropical regions in Asia and North America, and how the structures change through space and time. We also focus on understanding potential facilitation between earthworms belonging to different functional groups, the competition between invasive and naturalized species, and the interactions between the invaders and the native species.
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The soil food web experiences periodical nutrient pulses such as fertilizer addition and leaf fall. These pulses differ in timings, frequencies, and forms, leading to distinct responses in the soil food web. The periodical cicadas emerge from the soil every 13 or 17 years. Different “broods” of these unique species, which are only found in North America, emerge in specific regions in different years. We investigate how carcasses of 17-year cicadas change the nitrogen dynamics in the soil in temperate deciduous forests, and how members of the soil food web, especially mites, nematodes, and microbes, respond to the nutrient pulses.
Primary collaborator: Heikki Setälä (University of Helsinki); Katalin Szlavecz (Johns Hopkins University) |
Sampling earthworm communities is time consuming and labor intensive. Large-scale sampling is almost impossible due to limitations on funding, manpower, and the taxonomic expertise needed to correctly identify species. These constraints have become the biggest challenge when trying to understand how earthworm communities respond to global change and how the responses affect ecosystem functions. This NSF-funded project addresses this challenge by using soil samples collected by the National Ecological Observatory Network (NEON) from sites across the USA to understand how environmental factors affect earthworm diversity at the continental scale. We are developing new methodology that targets environmental DNA in the soil and uses Illumina sequencing for earthworm DNA metabarcoding. We then apply this method to NEON soil samples to achieve species-level earthworm identification across 47 terrestrial NEON sites covering all major biomes and ecological domains.
Primary collaborator: Katalin Szlavecz (Johns Hopkins University), Stephanie Yarwood (University of Maryland, College Park) |
In temperate soils, earthworms are important ecosystem engineers. Studies of invasive European species in North America have demonstrated that they impact ecosystem functions by redistributing nutrients in different pools in the soil and accelerating fluxes among the pools. Recently, another group of earthworms, the Asian Amynthas and Metaphire, has been reportedly found invading forests already inhabited by European species, causing a “second wave of invasion” where the soil ecosystem, already modified by European species, is going through another transition. The objective of this project is to understand how the invading Asian species compete with the “resident” European species and how these interactions alter soil microbial communities and C dynamics. We used carbon-13 and nitrogen-15 double-labeled leaf litter to trace the litter C into earthworm tissues, soil, and carbon dioxide flux, and conducted phospholipid fatty acid (PLFA) analysis to understand species-specific, earthworm-driven microbial community changes.
Primary collaborator: Katalin Szlavecz (Johns Hopkins University); Jeffery Buyer (USDA). |
Of the c.a. 180 earthworm species currently recorded in North America, about two-thirds, or 120 species, are native. But a large proportion of this diversity still remains undescribed or poorly understood. This project aims at understanding this diversity through discovering new species and investigating the evolutionary relationships of the involved genera. Currently we are focusing on discovering and describing new species of the genera Diplocardia and Bimastos in the Mid-Atlantic, and revising the systematics of the North America genus Bimastos.
Primary collaborator: Csaba Csuzdi (Eszterházy Károly University); Katalin Szlavecz (Johns Hopkins University). |
The invasion of the pheretimoid earthworms in North America, especially the genera Amynthas and Metaphire, has raised increasing concerns among ecologists and land managers. Many recent publications used Amynthas spp. to represent the group or inappropriately claimed Amynthas agrestis without properly identifying the species. This project aims at revising our knowledge on the invasive Asian earthworms of the genera Amynthas and Metaphire in North America, raising awareness of their invasion, and promoting correct species identification among researchers, land managers, and the general public. To provide a “field guide” for correctly identifying these invaders, we presented a new key that comes with illustrations for the 16 pheretimoid earthworm species recorded in North America. We summarized our current knowledge about their ecology, and highlighted the previously overlooked, and potentially common and widespread co-occurrence of three species, A. agrestis, A. tokioensis, and M. hilgendorfi. We also continue to help researchers around the US correctly identify earthworms from their field sites, and to monitor the ongoing invasion of the three Asian species.
Primary collaborator: Josef Görres (University of Vermont); Bruce Snyder (Georgia College & State University); Katalin Szlavecz (Johns Hopkins University) |