Genome Size in the Arenaria ciliata Species Complex (Caryophyllaceae), with Special Focus on Northern Europe and the Arctic

The main aim of the present study has been the completion of genome size data for the diverse arctic-alpine A. ciliata species complex, with special focus on the unexplored arctic taxon A. pseudofrigida, the north-European A. norvegica, and A. gothica from Gotland (Sweden). Altogether, 46 individuals of these three Nordic taxa have been sampled from seven different regions and their genome size estimated using flow cytometry. Three other alpine taxa in the A. ciliata complex (A. multicaulis, A. ciliata subsp. ciliata, and A. ciliata subsp. bernensis) were also collected and analyzed for standardization purposes, comprising 20 individuals from six regions. A mean 2c value of 1.65 pg of DNA was recorded for A. pseudofrigida, 2.80 pg for A. norvegica, and 4.14 pg for A. gothica, as against the reconfirmed 2c value of 1.63 pg DNA for the type taxon A. ciliata subsp. ciliata. Our results presenting the first estimations of genome sizes for the newly sampled taxa, corroborate ploidy levels described in the available literature, with A. pseudofrigida being tetraploid (2n = 4x = 40), A. norvegica possessing predominantly 2n = 8x = 80, and A. gothica with 2n = 10x = 100. The present study also reconfirms genome size and ploidy level estimations published previously for the alpine members of this species complex. Reflecting a likely complex recent biogeographic history, the A. ciliata species group comprises a polyploid arctic-alpine species complex characterized by reticulate evolution, polyploidizations and hybridizations, probably associated with rapid latitudinal and altitudinal migrations in the Pleistocene-Holocene period.

"Show me how to use a microscope" - The development and evaluation of certification as direct assessment of practical lab skills

Practical lab skills are rarely directly assessed. To improve constructive alignment between the described learning outcomes of practical skills and assessment, we developed and tested a certification procedure for microscopy skills. The procedure was embedded into the ordinary learning activity, so no additional time was needed. Three slightly different protocols were developed within the framework of sociocultural learning theory and built like a skill ladder, including direct peer assessment and elements of gamified learning. The protocols varied slightly in the way students were prepared for the certification, the number of steps/levels of achievement, and the consequences of failing. We tested the protocols at three different academic institutions and within 11 courses of varying sizes and academic levels in biology or geology. Feedbacks were collected through online surveys (n = 207) or orally after sessions. One protocol provided instruction videos as preparation material. Instruction videos provided increased understanding of the task, but tactile training was most important for learning. Regardless of institution, type of preparation, and level of former experience, the certification procedure made students clearly more engaged in the exercise. The majority reported that the certification procedure increased their motivation to learn, increased their perceived learning outcome, and was appropriate for assessing practical skills. Students with no or little experience in microscopy before the exercise were more positive about the certification procedure compared to skilled students, and the level of engagement and preparation was higher when there were some consequences of failing. Most students felt comfortable being certified by peers, but some students expressed concern about peers making mistakes. The presented certification procedure can easily be adapted to assess other practical skills and, with some adjustments, be an efficient method for assessment-as-learning, merging formative- and summative assessment.

Global maps of soil temperature

Research in global change ecology relies heavily on global climatic grids derived from estimates of air temperature in open areas at around 2 m above the ground. These climatic grids do not reflect conditions below vegetation canopies and near the ground surface, where critical ecosystem functions occur and most terrestrial species reside. Here, we provide global maps of soil temperature and bioclimatic variables at a 1-km2 resolution for 0-5 and 5-15 cm soil depth. These maps were created by calculating the difference (i.e. offset) between in situ soil temperature measurements, based on time series from over 1200 1-km2 pixels (summarized from 8519 unique temperature sensors) across all the world's major terrestrial biomes, and coarse-grained air temperature estimates from ERA5-Land (an atmospheric reanalysis by the European Centre for Medium-Range Weather Forecasts). We show that mean annual soil temperature differs markedly from the corresponding gridded air temperature, by up to 10°C (mean = 3.0 ± 2.1°C), with substantial variation across biomes and seasons. Over the year, soils in cold and/or dry biomes are substantially warmer (+3.6 ± 2.3°C) than gridded air temperature, whereas soils in warm and humid environments are on average slightly cooler (-0.7 ± 2.3°C). The observed substantial and biome-specific offsets emphasize that the projected impacts of climate and climate change on near-surface biodiversity and ecosystem functioning are inaccurately assessed when air rather than soil temperature is used, especially in cold environments. The global soil-related bioclimatic variables provided here are an important step forward for any application in ecology and related disciplines. Nevertheless, we highlight the need to fill remaining geographic gaps by collecting more in situ measurements of microclimate conditions to further enhance the spatiotemporal resolution of global soil temperature products for ecological applications.

Mapping nutrient resorption efficiencies of subarctic cryptogams and seed plants onto the Tree of Life

Nutrient resorption from senescing photosynthetic organs is a powerful mechanism for conserving nitrogen (N) and phosphorus (P) in infertile environments. Evolution has resulted in enhanced differentiation of conducting tissues to facilitate transport of photosynthate to other plant parts, ultimately leading to phloem. Such tissues may also serve to translocate N and P to other plant parts upon their senescence. Therefore, we hypothesize that nutrient resorption efficiency (RE, % of nutrient pool exported) should correspond with the degree of specialization of these conducting tissues across the autotrophic branches of the Tree of Life. To test this hypothesis, we had to compare members of different plant clades and lichens within a climatic region, to minimize confounding effects of climatic drivers on nutrient resorption. Thus, we compared RE among wide-ranging basal clades from the principally N-limited subarctic region, employing a novel method to correct for mass loss during senescence. Even with the limited numbers of species available for certain clades in this region, we found some consistent patterns. Mosses, lichens, and lycophytes generally showed low REN (<20%), liverworts and conifers intermediate (40%) and monilophytes, eudicots, and monocots high (>70%). REP appeared higher in eudicots and liverworts than in mosses. Within mosses, taxa with more efficient conductance also showed higher REN. The differences in REN among clades broadly matched the degree of specialization of conducting tissues. This novel mapping of a physiological process onto the Tree of Life broadly supports the idea that the evolution of conducting tissues toward specialized phloem has aided land plants to optimize their internal nitrogen recycling. The generality of evolutionary lines in conducting tissues and nutrient resorption efficiency needs to be tested across different floras in different climatic regions with different levels of N versus P availability.

Global assessment of experimental climate warming on tundra vegetation: heterogeneity over space and time

Understanding the sensitivity of tundra vegetation to climate warming is critical to forecasting future biodiversity and vegetation feedbacks to climate. In situ warming experiments accelerate climate change on a small scale to forecast responses of local plant communities. Limitations of this approach include the apparent site-specificity of results and uncertainty about the power of short-term studies to anticipate longer term change. We address these issues with a synthesis of 61 experimental warming studies, of up to 20 years duration, in tundra sites worldwide. The response of plant groups to warming often differed with ambient summer temperature, soil moisture and experimental duration. Shrubs increased with warming only where ambient temperature was high, whereas graminoids increased primarily in the coldest study sites. Linear increases in effect size over time were frequently observed. There was little indication of saturating or accelerating effects, as would be predicted if negative or positive vegetation feedbacks were common. These results indicate that tundra vegetation exhibits strong regional variation in response to warming, and that in vulnerable regions, cumulative effects of long-term warming on tundra vegetation - and associated ecosystem consequences - have the potential to be much greater than we have observed to date.

Strong microsite control of seedling recruitment in tundra

The inclusion of environmental variation in studies of recruitment is a prerequisite for realistic predictions of the responses of vegetation to a changing environment. We investigated how seedling recruitment is affected by seed availability and microsite quality along a steep environmental gradient in dry tundra. A survey of natural seed rain and seedling density in vegetation was combined with observations of the establishment of 14 species after sowing into intact or disturbed vegetation. Although seed rain density was closely correlated with natural seedling establishment, the experimental seed addition showed that the microsite environment was even more important. For all species, seedling emergence peaked at the productive end of the gradient, irrespective of the adult niches realized. Disturbance promoted recruitment at all positions along the environmental gradient, not just at high productivity. Early seedling emergence constituted the main temporal bottleneck in recruitment for all species. Surprisingly, winter mortality was highest at what appeared to be the most benign end of the gradient. The results highlight that seedling recruitment patterns are largely determined by the earliest stages in seedling emergence, which again are closely linked to microsite quality. A fuller understanding of microsite effects on recruitment with implications for plant community assembly and vegetation change is provided.

Similar cation exchange capacities among bryophyte species refute a presumed mechanism of peatland acidification

Fen-bog succession is accompanied by strong increases of carbon accumulation rates. We tested the prevailing hypothesis that living Sphagna have extraordinarily high cation exchange capacity (CEC) and therefore acidify their environment by exchanging tissue-bound protons for basic cations in soil water. As Sphagnum invasion in a peatland usually coincides with succession from a brown moss-dominated alkaline fen to an acidic bog, the CEC of Sphagna is widely believed to play an important role in this acidification process. However, Sphagnum CEC has never been compared explicitly to that of a wide range of other bryophyte taxa. Whether high CEC directly leads to the ability to acidify the environment in situ also remains to be tested. We screened 20 predominant subarctic bryophyte species, including fen brown mosses and bog Sphagna for CEC, in situ soil water acidification capacity (AC), and peat acid neutralizing capacity (ANC). All these bryophyte species possessed substantial CEC, which was remarkably similar for brown mosses and Sphagna. This refutes the commonly accepted idea of living Sphagnum CEC being responsible for peatland acidification, as Sphagnum's ecological predecessors, brown mosses, can do the same job. Sphagnum AC was several times higher than that of other bryophytes, suggesting that CE (cation exchange) sites of Sphagna in situ are not saturated with basic cations, probably due to the virtual absence of these cations in the bog water. Together, these results suggest that Sphagna can not realize their CEC in bogs, while fen mosses can do so in fens. The fen peat ANC was 65% higher than bog ANC, indicating that acidity released by brown mosses in the CE process was neutralized, maintaining an alkaline environment. We propose two successional pathways indicating boundaries for a fen-bog shift with respect to bryophyte CEC. In neither of them is Sphagnum CE an important factor. We conclude that living Sphagnum CEC does not play any considerable role in the fen-bog shift. Alternatively, we propose that exclusively indirect effects of Sphagnum expansion such as peat accumulation and subsequent blocking of upward alkaline soil water transport are keys to the fen-bog succession and therefore for bog-associated carbon accumulation.

The contribution of mosses to the carbon and water exchange of Arctic ecosystems: quantification and relationships with system properties

Water vapour and CO2 exchange were measured in moss-dominated vegetation using a gas analyser and a 0.3 x 0.3 m chamber at 17 sites near Abisko, Northern Sweden and 21 sites near Longyearbyen, Svalbard, to quantify the contribution of mosses to ecosystem level fluxes. With the help of a simple light-response model, we showed that the moss contribution to ecosystem carbon uptake varied between 14 and 96%, with an average contribution of around 60%. This moss contribution could be related to the normalized difference vegetation index (NDVI) of the vegetation and the leaf area index (LAI) of the vascular plants. NDVI was a good predictor of gross primary production (GPP) of mosses and of the whole ecosystem, across different moss species, vegetation types and two different latitudes. NDVI was also correlated with thickness of the active green moss layer. Mosses played an important role in water exchange. They are expected to be most important to gas exchange during spring when leaves are not fully developed.

Comparative cryptogam ecology: a review of bryophyte and lichen traits that drive biogeochemistry

BACKGROUND

Recent decades have seen a major surge in the study of interspecific variation in functional traits in comparative plant ecology, as a tool to understanding and predicting ecosystem functions and their responses to environmental change. However, this research has been biased almost exclusively towards vascular plants. Very little is known about the role and applicability of functional traits of non-vascular cryptogams, particularly bryophytes and lichens, with respect to biogeochemical cycling. Yet these organisms are paramount determinants of biogeochemistry in several biomes, particularly cold biomes and tropical rainforests, where they: (1) contribute substantially to above-ground biomass (lichens, bryophytes); (2) host nitrogen-fixing bacteria, providing major soil N input (lichens, bryophytes); (3) control soil chemistry and nutrition through the accumulation of recalcitrant polyphenols (bryophytes) and through their control over soil and vegetation hydrology and temperatures; (4) both promote erosion (rock weathering by lichens) and prevent it (biological crusts in deserts); (5) provide a staple food to mammals such as reindeer (lichens) and arthropodes, with important feedbacks to soils and biota; and (6) both facilitate and compete with vascular plants.

APPROACH

Here we review current knowledge about interspecific variation in cryptogam traits with respect to biogeochemical cycling and discuss to what extent traits and measuring protocols needed for bryophytes and lichens correspond with those applied to vascular plants. We also propose and discuss several new or recently introduced traits that may help us understand and predict the control of cryptogams over several aspects of the biogeochemistry of ecosystems.

CONCLUSIONS

Whilst many methodological challenges lie ahead, comparative cryptogam ecology has the potential to meet some of the important challenges of understanding and predicting the biogeochemical and climate consequences of large-scale environmental changes driving shifts in the cryptogam components of vegetation composition.