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ABSTRACTThis paper presents a compilation of atmospheric radiocarbon for the period 1950–2019, derived from atmospheric CO2sampling and tree rings from clean-air sites. Following the approach taken by Hua et al. (2013), our revised and extended compilation consists of zonal, hemispheric and global radiocarbon (14C) data sets, with monthly data sets for 5 zones (Northern Hemisphere zones 1, 2, and 3, and Southern Hemisphere zones 3 and 1–2). Our new compilation includes smooth curves for zonal data sets that are more suitable for dating applications than the previous approach based on simple averaging. Our new radiocarbon dataset is intended to help facilitate the use of atmospheric bomb 14C in carbon cycle studies and to accommodate increasing demand for accurate dating of recent (post-1950) terrestrial samples.

ABSTRACTSince the 1950s, observations of radiocarbon (14C) in tropospheric carbon dioxide (CO2) have been conducted in both hemispheres, documenting the so-called nuclear “bomb spike” and its transfer into the oceans and the terrestrial biosphere, the two compartments permanently exchanging carbon with the atmosphere. Results from the Heidelberg global network of Δ14C-CO2observations are revisited here with respect to the insights and quantitative constraints they provided on these carbon exchange fluxes. The recent development of global and hemispheric trends of Δ14C-CO2are further discussed in regard to their suitability to continue providing constraints for 14C-free fossil CO2emission changes on the global and regional scale.

Radiocarbon (14C) is a powerful tracer of fossil emissions because fossil fuels are entirely depleted in 14C, but observations of 14CO2and especially 14CH4in urban regions are sparse. We present the first observations of 14C in both methane (CH4) and carbon dioxide (CO2) in an urban area (London) using a recently developed sampling system. We find that the fossil fraction of CH4and the atmospheric concentration of fossil CO2are consistently higher than simulated values using the atmospheric dispersion model NAME coupled with emission inventories. Observed net biospheric uptake in June–July is not well correlated with simulations using the SMURF model with NAME. The results show the partitioning of fossil and biospheric CO2and CH4in cities can be evaluated and improved with 14C observations when the nuclear power plants influence is negligible. Radiocarbon (14C) is an ideal tracer of fossil emissions, as fossil fuels have lost all 14C during millions of years of burial underground. When fossil carbon is re‐introduced into the atmosphere, it exerts a strong dilution of the radiocarbon to total carbon ratio. By measuring this ratio in the atmosphere, we can quantify fossil methane and carbon dioxide emissions. This is the first combined study of 14C in both atmospheric methane and carbon dioxide at regional scale. Atmospheric radiocarbon measurements in central London reveal higher fossil CH4and CO2present, compared to simulationsRadiocarbon measurements show biospheric uptake of CO2in July that is stronger than simulationsNuclear power plants interfere with radiocarbon measurements in London when air is coming from Europe Atmospheric radiocarbon measurements in central London reveal higher fossil CH4and CO2present, compared to simulations Radiocarbon measurements show biospheric uptake of CO2in July that is stronger than simulations Nuclear power plants interfere with radiocarbon measurements in London when air is coming from Europe

AbstractIn 2008, the atmospheric CO2measurements at the Hegyhátsál rural tower station were extended further by 14CO2air sampling from two elevations (115 and 10 m a.g.l.), in cooperation with HEKAL (ICER). Since then, a complete six-year-long (2008–2014) dataset of atmospheric CO2, Δ14C, fossil, and modern CO2excess (relative to Jungfraujoch) has been assembled and evaluated. Based on our results, the annual mean CO2mole fraction rose at both elevations in this period. The annual mean Δ14CO2values decreased with a similar average annual decline. Based on our comparison, planetary boundary layer height obtained by modeling has a larger influence on the variation of mole fraction of CO2(relative to Jungfraujoch), than on its carbon isotopic composition, i.e. the boundary layer rather represents a physical constraint. Fossil fuel CO2excess at both elevations can rather be observed in wintertime and mainly due to the increased anthropogenic emission of nearby cities in the region. The mean modern CO2excess at both elevations was even larger in winter, but it drastically decreased at 115 m by summer, while it remained at the winter level at 10 m.

This paper discusses undergraduate training in a small group field research setting, as a response to larger issues of biodiversity and scientific specialization. It describes student empowerment, the development of critical thinking skills, and the importance of group dynamics. It also explores how to introduce and perpetuate an innovative approach to scientific learning.

AbstractThe morphogenesis of Cladonia strepsilis, which is poorly understood, is determined by its fungal meristem tissue. The meristem follows a variable developmental pattern that results in podetia with a range of morphologies. Early ontogeny of the meristem includes combinations of splitting, enlarging, and budding, which give rise to mature podetia that are difficult to characterize. The growth dynamics of C. strepsilisresembles that of other presumably unrelated taxa within Cladonia.Its heterogeneous ontogeny is considered as primitive. Development in this species is best interpreted as a continuous process that gives rise to a number of related forms. A process morphology interpretation of C. strepsilisprovides insights into the possible relationships of this species, which may belong in section Perviae.

Morphogenesis of podetia inCladonia subcervicornisis a non-linear, repeating process based upon a pattern of meristem enlargement and division. Variability in mature podetia ofC. subcervicornis, which may appear branched or scyphoid, is the result of variation early in ontogeny. The growth pattern ofC. subcervicornisrepresents a continuum of developmental stages. It is impossible to predict the form of the mature thallus ofC. subcervicornisbecause growth in this species is fluid. The morphology of the mature thallus ofC. subcervicornisis difficult to circumscribe using conventionalCladoniaterminology, because the processes that form the thallus are dynamic and heterogeneous. The meristem shapes that are produced during early ontogeny inC. subcervicornisare relatively simple, and the processes by which they are formed are uncomplicated. Yet podetial form inC. subcervicornisis difficult to interpret.

Cladina subtenuisestablishes and expands by mechanisms of the thallus mycobiont. Vegetative reproduction occurs through thallus fragmentation, branch ‘de-differentiation’, and the extension of the underground prothallus. Establishment hyphae can be considered as any hyphae that provide the mechanism for these modes of clonal thallus extension. They may originate in various parts of the thallus, laterally on branch surfaces, at the growing tips of branches, or from the inner fungal layers of the podetium. The thallus ofC. subtenuisis structurally and functionally plastic. Parts of the photosynthetic lichen thallus can transform into non-photosynthetic fungal aggregations, and non-photosynthetic aggregations may re-establish as a photosynthetic lichen thallus. These activities expand the area occupied by the clone, and potentially increase its photosynthetic surface.

AbstractThe erect secondary thallus (podetium) of the lichen Cladonia grayidevelops in distinct stages that can be traced to the development of its fungal meristem tissue. In early ontogeny, while the contiguous meristem grows unilaterally both outward and vertically, the gross morphology of the podetium resembles other cup-forming species. In later ontogeny, when the divided meristem grows vertically, the podetium forms a subtly articulated spiral. The spiral growth form is most apparent in branching proliferations that grow along the cup margin. The meristem tissue at the apex of these proliferations is curved, maturing sequentially in a spiral pattern. The proliferations curve in a spiral around the vertical axis of the podetium. Apothecia at the apex of proliferations curve in a similar manner. Evidence for spiral growth along the cup margin can also be inferred from the sequential development of pycnidia that emerge from it. Similar to early land plants, the growth dynamics of C. grayimay represent an evolutionary advance from an orthotropous growth pattern to a branched, photosynthetic thallus.

AbstractThe fruticose thallus of mature Cladina subtenuisis characterized by a variable branching pattern. While the shape of the mature thallus is not easily predictable, early branch initiation follows a highly predictable pattern. Branching is determined by meristemlike bundles of fungal cells located at the apices of the thallus. When the bundles split, branching is initiated. Meristem growth is limited to a uniform developmental pattern of dichotomous, sequential divisions of the fungal bundles. Filial meristem bundles, the result of a single division, comprise a developmental unit. Their subsequent divisions, which are sequential, produce meristem initials of three or five bundles. Branching is constrained by this pattern, but variability is introduced by the differential elongation and orientation of certain branches. Variability may arise in response to growth conditions such as the proximity of other branches or environmental conditions, for example light availability. The ability to elaborate on the basic plan of development permits radial expansion and increased photosynthetic opportunities for the thallus of C. subtenuis.