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During litter decomposition, three major fates of litter carbon (C) are possible: emission as carbon dioxide (CO2) into the atmosphere, leaching of dissolved organic carbon (DOC), and translocation and transformation into soil organic carbon (SOC). Soil moisture, one of the key drivers of litter decomposition, is predicted to change in the future due to shifts in precipitation patterns. We explored the effects of low, medium and high rainfall intensities on the partitioning of litter carbon fates in a 6-month long laboratory experiment. We tracked carbon in 13C-labeled tulip poplar litter in a laboratory mesocosms by measuring respiration rates, dissolved organic carbon in the leachate, and soil organic carbon at the end of the experiment. Mesocosms with the same three rainfall intensities but without leaf litter were also set up. Leaching of labile carbon caused priming, but the effect was stronger in the low intensity treatment. Transport of litter-derived carbon also differed: in high intensity treatment there was more total carbon in the surface soil and more litter-derived carbon in in the deep soil layers. The cumulative CO2 efflux was not significantly different. Our results highlight that extreme rainfall events, as projected by most climate models, may lead to altered carbon cycling in temperate forest soils.

Forests are major sources of terrestrial CH4 and CO2 fluxes but not all surfaces within forests have been measured and accounted for. Stem respiration is a well-known source of CO2, but more recently tree stems have been shown to be sources of CH4 in wetlands and upland habitats. A study transect was established along a natural moisture gradient, with one end anchored in a forested wetland, the other in an upland forest and a transitional zone at the midpoint. Stem and soil fluxes of CH4 and CO2 were measured using static chambers during the 2013 and 2014 growing seasons, from May to October. Mean stem CH4 emissions were 68.8 ± 13.0 (mean ± standard error), 180.7 ± 55.2 and 567.9 ± 174.5 µg m−2 h−1 for the upland, transitional and wetland habitats, respectively. Mean soil methane fluxes in the upland, transitional and wetland were − 64.8 ± 6.2, 7.4 ± 25.0 and 190.0 ± 123.0 µg m−2 h−1, respectively. Measureable CH4 fluxes from tree stems were not always observed, but every individual tree in our experiment released measureable CH4 flux at some point during the study period. These results indicate that tree stems represent overlooked sources of CH4 in forested habitats and warrant investigation to further refine CH4 budgets and inventories.

Summary Global budgets ascribe 4–10% of atmospheric methane (CH4) sinks to upland soils and have assumed until recently that soils are the sole surface for CH4 exchange in upland forests. Here we report that CH4 is emitted from the stems of dominant tree species in a temperate upland forest, measured using both the traditional static-chamber method and a new high-frequency, automated system. Tree emissions averaged across 68 observations on 17 trees from May to September were 1.59 ± 0.88 μmol CH4 m−2 stem h−1 (mean ± 95% confidence interval), while soils adjacent to the trees consumed atmospheric CH4 at a rate of −4.52 ± 0.64 μmol CH4 m−2 soil h−1 (P

In temperate deciduous forests of eastern USA, most earthworm communities are dominated by invasive species. Their structure and functional group composition have critical impacts on ecological properties and processes. However, the factors determining their community structure are still poorly understood, and little is known regarding their dynamics during forest succession and the mechanisms leading to these changes. Earthworm communities are usually assumed to be stable and driven by vegetation. In contrast, the importance of dispersal and ecological drift is seldom acknowledged. By analyzing a 19-year dataset collected from forest stands in eastern USA, we demonstrated that on a decadal timescale, earthworm community dynamics are shaped by the interplay of selection, dispersal, and ecological drift. We highlighted that forests at different successional stages have distinct earthworm species and functional groups as a result of environmental filtering through leaf litter quality. Specifically, young forests are characterized by soil-feeding species that rely on relatively fresh soil organic matter derived from fast-decomposing litter, whereas old forests are characterized by those feeding on highly processed soil organic matter derived from slow-decomposing litter. In addition, year-to-year species gains and losses are primarily driven by dispersal from regional to local species pools, and by local extinction resulted from competition and ecological drift. We concluded that with continued dispersal of European species and the recent "second wave" of earthworm invasion by Asian species from the surrounding landscape, earthworms at the investigated forests are well-established, and will remain as the major drivers of soil development for the foreseeable future.

Substrates with a unique stable isotope signature provide researchers with the ability to trace nutrients through food webs. Plant material labeled with carbon (13C) can be produced by exposure to carbon dioxide (CO2) with an isotopic composition that differs from ambient conditions during photosynthesis. Labeling can occur continuously or be repeated over several “pulses.” Each method has a high cost either in the form of expensive control systems or significant time investments. In 2012, we built a large growth chamber and used an inexpensive, open-source ArduinoTM microcontroller to monitor and control interior conditions so that we could produce leaf litter dually enriched in 13C and nitrogen (15N) for future incubation experiments. We performed a labeling experiment on 73 saplings representing seven species in 2012 and repeated the labeling on 30 saplings of one species in 2013. We successfully produced over 1 kg of litter enriched in both isotopes; 15N-enrichment (δ15N: 759.2 ± 133.7‰) was much grea...

Earthworms influence the biotic and abiotic characteristics of soils, but studying these effects in situ is challenging. Secondary forests in the Mid-Atlantic have abundant earthworm communities. To investigate the interaction of earthworms with the below- and aboveground part of the ecosystem, we manipulated earthworm densities in 1 m 2 enclosures located at 12 study sites within four different-aged forest stands at the Smithsonian Environmental Research Center (SERC) in Maryland, USA. The treatment plots were created by trenching around the perimeter and lining the trenches with fiberglass mesh before backfilling. Two types of untrenched plots served as control and leaf litter treatment plots. Enclosures were electroshocked between four and nine times over a two-year period to remove earthworms and to compare densities among treatment and untrenched plots. Earthworms were weighed and identified to determine whether removal by electroshocking varied depending on body size or ecological grouping. Earthworm abundances were 30–50% lower in reduced-density enclosures than in high density enclosures; however, the efficiency of the exclusion treatments varied by earthworm size and ecological group. Manipulating earthworm populations in temperate forests to assess their influence on ecological functions is feasible using electroshocking, but careful planning is essential given the amount of effort required to set up and maintain the desired experimental conditions.

The factors regulating soil animal communities are poorly understood. Current theory favors niche complementarity and facilitation over competition as the primary forms of non-trophic interspecific interaction in soil fauna; however, competition has frequently been suggested as an important community-structuring factor in earthworms, ecosystem engineers that influence belowground processes. To date, direct evidence of competition in earthworms is lacking due to the difficulty inherent in identifying a limiting resource for saprophagous animals. In the present study, we offer the first direct evidence of interspecific competition for food in this dominant soil detritivore group by combining field observations with laboratory mesocosm experiments using 13C and 15N double-enriched leaf litter to track consumption patterns. In our experiments, the Asian invasive species Amynthas hilgendorfi was a dominant competitor for leaf litter against two European species currently invading the temperate deciduous forests in North America. This competitive advantage may account for recent invasion success of A. hilgendorfi in forests with established populations of European species, and we hypothesize that specific phenological differences play an important role in determining the outcome of the belowground competition. In contrast, Eisenoides lonnbergi, a common native species in the Eastern United States, occupied a unique trophic position with limited interactions with other species, which may contribute to its persistence in habitats dominated by invasive species. Furthermore, our results supported neither the hypothesis that facilitation occurs between species of different functional groups nor the hypothesis that species in the same group exhibit functional equivalency in C and N translocation in the soil. We propose that species identity is a more powerful approach to understand earthworm invasion and its impacts on belowground processes.