Germination and seedling growth of Calluna vulgaris is sensitive to regional climate, heathland succession, and drought

The coastal heathlands of Northwest Europe are highly valued cultural landscapes, that are critically endangered due to land use and climatic changes, such as increased frequency and severity of drought events. Our study is the first to assess how the germination and early seedling growth of Calluna vulgaris respond to drought. In a factorial design field experiment, we exposed maternal plants to three in-situ drought treatments (control, 60%, 90% roof coverage), across three successional stages after fire (pioneer, building, mature), and two regions (60°N, 65°N). Seeds from 540 plants within the experiment were, weighed, and exposed to five water potentials, ranging from −0.25 to −1.7 MPa, in a growth chamber experiment. We recorded germination (percentage, rate), seedling growth (above- vs. belowground allocation), and seedling functional traits (specific leaf area [SLA], specific root length [SRL]). Overall variation in germination between regions, successional stages, and maternal drought treatments was largely mediated by variation in seed mass. Plants from the northernmost region had higher seed mass and germination percentages. This is indicative of higher investment in seeds, likely linked to the populations' absence of vegetative root sprouting. Seeds from the mature successional stage germinated to lower final percentages than those from earlier successional stages, especially when the maternal plants had been exposed to drought (60% and 90% roof coverage). Exposure to reduced water availability decreased germination percentage and increased the time to 50% germination. Seedlings fully developed in the range −0.25 to −0.7 MPa, with increased root:shoot and lower SRL during reduced water availability, suggesting a resource-conservative response to drought during the early stages of development. Our results thus suggest a sensitivity to drought during the germination and seedling life-history stages that may reduce Calluna's ability to re-establish from seeds as the incidence and severity of droughts are projected to increase under future climates.publishedVersio

Functional traits of alpine plant communities show long-term resistance to changing herbivore densities

Herbivores shape vegetation by suppressing certain plant species while benefitting others. By thus modifying plant species functional composition, herbivores affect carbon cycling, albedo, vegetation structure and species' interactions. These effects have been suggested to be able to counteract the effects of increasing temperatures on vegetation in alpine environments. Managing the dominant large ungulates in these ecosystems could thus provide a tool to mitigate climate change effects. However, it is possible that legacy effects of past grazing will dampen ungulate impacts on vegetation. We shed a light on this topic by investigating the short- and long-term effects of varying sheep densities on the plant trait composition in the Norwegian alpine tundra with centuries-long of intensive grazing history. In the first part of our study, we quantified the effects of sheep on the plant community functional trait composition at different elevations and under moderate and low productivity in. We combined data from two long-term (14 and 19 yr) sheep fence experiments and showed that differences in sheep densities did not affect plant trait composition, irrespective of productivity. However, in the second part of our study, we showed that the plant trait composition in mainland (that has been grazed for centuries) differed from vegetation on islands which have been herbivore-free. Taken together, these results suggest that sheep have an effect on the alpine plant communities on historical time scales covering centuries, but that the resulting sheep grazing resistant/tolerant communities may not respond to shorter-term (14 and 19 yr) changes in sheep densities, that is, at temporal scales relevant for ecosystem management. Furthermore, we showed that the plant trait composition at the site with low productivity had gone through a temporal trait change independent of sheep treatment, potentially due to increased temperatures and precipitation, suggesting that sheep may not be able to counteract climatic impacts in the areas with centuries-long grazing history.publishedVersio

The handbook for standardized field and laboratory measurements in terrestrial climate change experiments and observational studies (ClimEx)

Climate change is a world-wide threat to biodiversity and ecosystem structure, functioning and services. To understand the underlying drivers and mechanisms, and to predict the consequences for nature and people, we urgently need better understanding of the direction and magnitude of climate change impacts across the soil-plant-atmosphere continuum. An increasing number of climate change studies are creating new opportunities for meaningful and high-quality generalizations and improved process understanding. However, significant challenges exist related to data availability and/or compatibility across studies, compromising opportunities for data re-use, synthesis and upscaling. Many of these challenges relate to a lack of an established 'best practice' for measuring key impacts and responses. This restrains our current understanding of complex processes and mechanisms in terrestrial ecosystems related to climate change. To overcome these challenges, we collected best-practice methods emerging from major ecological research networks and experiments, as synthesized by 115 experts from across a wide range of scientific disciplines. Our handbook contains guidance on the selection of response variables for different purposes, protocols for standardized measurements of 66 such response variables and advice on data management. Specifically, we recommend a minimum subset of variables that should be collected in all climate change studies to allow data re-use and synthesis, and give guidance on additional variables critical for different types of synthesis and upscaling. The goal of this community effort is to facilitate awareness of the importance and broader application of standardized methods to promote data re-use, availability, compatibility and transparency. We envision improved research practices that will increase returns on investments in individual research projects, facilitate second-order research outputs and create opportunities for collaboration across scientific communities. Ultimately, this should significantly improve the quality and impact of the science, which is required to fulfil society's needs in a changing world.Peer reviewe

The handbook for standardized field and laboratory measurements in terrestrial climate change experiments and observational studies (ClimEx)

1. Climate change is a world‐wide threat to biodiversity and ecosystem structure, functioning and services. To understand the underlying drivers and mechanisms, and to predict the consequences for nature and people, we urgently need better understanding of the direction and magnitude of climate change impacts across the soil–plant–atmosphere continuum. An increasing number of climate change studies are creating new opportunities for meaningful and high‐quality generalizations and improved process understanding. However, significant challenges exist related to data availability and/or compatibility across studies, compromising opportunities for data re‐use, synthesis and upscaling. Many of these challenges relate to a lack of an established ‘best practice’ for measuring key impacts and responses. This restrains our current understanding of complex processes and mechanisms in terrestrial ecosystems related to climate change. 2. To overcome these challenges, we collected best‐practice methods emerging from major ecological research networks and experiments, as synthesized by 115 experts from across a wide range of scientific disciplines. Our handbook contains guidance on the selection of response variables for different purposes, protocols for standardized measurements of 66 such response variables and advice on data management. Specifically, we recommend a minimum subset of variables that should be collected in all climate change studies to allow data re‐use and synthesis, and give guidance on additional variables critical for different types of synthesis and upscaling. The goal of this community effort is to facilitate awareness of the importance and broader application of standardized methods to promote data re‐use, availability, compatibility and transparency. We envision improved research practices that will increase returns on investments in individual research projects, facilitate second‐order research outputs and create opportunities for collaboration across scientific communities. Ultimately, this should significantly improve the quality and impact of the science, which is required to fulfil society's needs in a changing world

The role of intraspecific variability in driving community trait shifts along temperature and precipitation gradients in alpine and boreal semi-natural grasslands

Climate projections show that western Norway will experience warmer and wetter conditions in the future. Investigations of trait changes with these climatic gradients can be used to understand the responses of species, communities and ecosystems to climate change. A main assumption within trait-based ecology has been that the variation in traits is larger between species than within species, and hence that mean-species-level trait values can be used in various applications of trait-based ecology. Recent studies find intraspecific trait variability to represent an unneglectable proportion of the total trait variability, and to play an important role in the ecosystems. In this study, I investigated how the trait of alpine and boreal semi-natural grassland plants change with temperature (6.5-10.5 mean temperature in the four warmest months), and precipitation (650-2900 mm/year). All together 2780 leaves from 88 species were collected and used to calculate these functional traits; specific leaf area (SLA), leaf dry matter content (LDMC), leaf thickness, carbon to nitrogen ratio and vegetative height, which are all related to the leaf economic spectrum. Community trait distributions change due to different abiotic and biotic stressors in the interaction between temperature and precipitation. These trends are driven by both intraspecific variability and species turnover effect, and some, but far from all species show patterns in the intraspecific variability that match the community-wide patterns. This study provides evidence that intraspecific trait variability in alpine and boreal semi-natural grasslands is relatively high compared to other habitats, ant that it contributes to shape gradient-wide patterns. The warmer and wetter alpine grasslands of the future are likely to lead to changes in species composition, traits, and ecosystem functioning of these habitats caused by increased abundance of species and genotypes with higher photosynthetic capacity. This change could be caused by shifts in trait distribution by species migrating into these habitats, or species already present, driven by the high proportion of intraspecific variability or by a shift in species abundance. For trait-based ecology these findings imply that the need for including intraspecific variability, by sampling local traits, should be considered for alpine grasslands

Disentangling effects and context dependencies of climate change on alpine plants

Klimaendringer byr på nye utfordringer for fjellplanter, og påvirker dem både direkte gjennom å endre fysiologiske prosesser, og indirekte gjennom endringer i interaksjoner mellom planter. Disse indirekte effektene kan være forårsaket av økt intensitet av konkurrerende interaksjoner mellom arter som allerede er til stede i det nåværende plantesamfunnet. I tillegg kan endringer i interaksjoner også være forårsaket av helt nye interaksjoner som dukker opp når arter fra lavlandet utvider sin utbredelse til fjellene. Slike indirekte effekter av klimaendringer kan være viktige – de kan vesentlig modifisere omfanget eller til og med snu retningen på de direkte effektene. Få studier har eksplisitt separert bidragene fra disse direkte og indirekte effektene av klimaendringer på fjellplanter tidligere. I denne oppgaven kombinerer jeg ulike tilnærminger for å teste de direkte og indirekte effektene av klimaendringer på økologiske prosesser i plantesamfunnene på fjellet og deres individer og populasjoner. I studier med fokus på samfunnsnivå brukte jeg tolv lokaliteter i et klimagrid som varierer i temperatur og nedbør. Jeg kombinerte data fra et observasjonsstudie over en tiårsperiode med funksjonelle trekk for å se etter bevis på endring i funksjonell sammensetningen av plantesamfunn, og om disse endringene samsvarer med prediksjoner fra endringer langs klimagradientene. I studier med fokus på individer og populasjoner bruker jeg to vanlige fjellplanter med litt forskjellige nisjer og habitatselektivitet: Veronica alpina, en generalist på fjellet og Sibbaldia procumbens, en snøleiespesialist. Jeg bruker laboratorieforsøk for å undersøke effekten av tørke på spiringsprosesser og frøplanter av disse artene. Og til slutt bruker jeg demografiske studier i et felteksperiment for å skille ut mekanismene som ligger til grunn for de direkte og indirekte effektene av klimaendringer på disse artene. Eksperimentet er designet for å eksplisitt skille direkte effekter av oppvarming fra indirekte effekter som virker enten gjennom endringer i nåværende artsinteraksjoner eller i nye artsinteraksjoner. Begge eksperimentene er utført langs en nedbørsgradient for å undersøke kontekstavhengigheter i disse økologiske prosessene. Etter hvert som studieregionen min i Sørvest-Norge har blitt varmere og våtere, har plantesamfunnene endret seg mot å bli mer dominert av høyere arter med blader med høy fotosyntesekapasitet. Likevel var disse funksjonsendringene i vegetasjonen mindre enn forventet basert på klimaresponsen langs temperatur- og nedbørsgradienter i samme region. Felt- og laboratorieeksperimentene tillot meg å utforske to direkte effekter av klimaendringer: oppvarming og tørke. Oppvarming alene ser ut til å påvirke fjellplanter ved å øke veksten og overlevelsen, noe som fører til økt populasjonsvekstrate. Derimot har tørke en negativ effekt på spiring og frøplantes overlevelse. Disse resultatene varierer mellom populasjoner langs nedbørsgradienten, og mellom arter. Generalisten (V. alpina) hadde en mer positiv respons på oppvarming enn snøleiespesialisten (S. procumbens). Videre viste V. alpina også tegn på lokale tilpasninger til tørke i de tørreste bestandene, i motsetning til S. procumbens, og for begge artene hadde populasjoner fra tørrere habitater en større positiv respons fra oppvarming. I denne avhandlingen fant jeg at klimaendringer har positive direkte effekter på mange aspekter av livshistorien til fjellplanter, men at disse effektene faktisk kan dempes eller til og med reverseres av indirekte klimaendringer som virker via interaksjoner mellom planter. Fjellplantene i fokus i denne avhandlingen påvirkes av konkurrerende (V. alpina) eller nøytrale (S. procumbens) interaksjoner i dagens fjellplantesamfunn og klima. Med oppvarming øker intensiteten av konkurrerende interaksjoner innad i fjellplantesamfunnene. I tillegg vil introduksjon av nye, mer konkurrerende interaksjoner via lavlandsarter som flytter seg opp i fjellet, reduserer den positive effekten av oppvarming ytterligere. Igjen var snøleiespesialisten mest sensitiv til økt konkurranse, og de indirekte effektene varierte også med nedbør, noe som indikerte at den negative effekten av økt konkurranse var sterkest i de våtere lokalitetene og for spesialiserte fjellplanter.Climate change poses new challenges for alpine plants, affecting them both directly through altering physiological processes, and indirectly through changes in species’ interactions. These indirect effects could be caused by increased intensity of competitive plant-plant interactions among species already present in the current plant community. Additionally, changes in interactions could also be caused by entirely novel interactions emerging as species from lower elevations expand their ranges into the mountains. Such indirect effects of climate change can be important - significantly modifying the magnitude or even reversing the direction of the direct effects. Few studies have explicitly disentangled the contributions of these direct and indirect effects of climate change on alpine plants. In this thesis I combine different approaches to test the direct and indirect effects of climate change on ecological processes involving alpine plant communities and their individuals and populations. In studies focusing on communities, I used a twelve-site climate grid that varies in temperature and precipitation, where I combined data from an observational study over a ten-year period with site-level functional trait data to look for evidence of change in functional composition of alpine communities, and whether these changes match predictions from the climate gradients. In studies focusing on individuals and populations, I use two common alpine plants with slightly different niches and habitat selectivity: Veronica alpina, an alpine generalist and Sibbaldia procumbens, a snowbed specialist. I use laboratory experiments to investigate the effect of drought on germination and seedlings of these focal alpine plants. And finally, I use demographic studies in a field experiment to disentangle the mechanisms underlying the direct and the indirect effects of climate change on these focal species. The experiment is designed to explicitly disentangle direct effects of warming from indirect effects operating through either change in current species interactions or in novel species interactions. Both experiments are conducted along a precipitation gradient to assess context-dependencies in the responses. As my study region in southwestern Norway has become warmer and wetter, alpine plant communities have shifted towards being more dominated by taller species with more resource-acquisitive leaves. Still, these functional changes in the vegetation were smaller than expected based on the climate response along temperature and precipitation gradients in the same region. The field and lab experiments allowed me to single out two direct effects of climate change: warming and drought. Warming alone seems to impact alpine plants by increasing growth and survival, leading to increased population growth rates. In contrast drought has a negative effect on germination and seedling survival. These results vary between populations along the precipitation gradient, and between species. The alpine generalist (V. alpina) had a more positive response to warming than the snowbed specialist (S. procumbens). Further, V. alpina also showed signs of local adaptations to drought in the driest populations, as opposed to S. procumbens, and for both species, populations from drier habitats had a larger positive response to warming. In this thesis I found that warming alone has positive direct effects on many aspects of the life-histories of alpine plants, but that these effects can in fact be dampened or even reversed by indirect climate change effects operating via species’ interactions. The alpine focal plants are affected by competitive (V. alpina) or neutral (S. procumbens) interactions within the current alpine vegetation and climate. With warming the intensity of competitive interactions within the current alpine vegetation increases. Introducing novel interactions from range-expanding sub-alpine species, especially with more competitive traits, further increases competition and reduces the positive effect of warming. The indirect effects also varied with precipitation, indicating that the negative effect of species interactions is strongest in the wetter sites.Doktorgradsavhandlin

Taking practical learning in STEM education home: Examples from do‐it‐yourself experiments in plant biology

Practical teaching can give authentic learning experiences and teach valuable skills for undergraduate students in the STEM disciplines. One of the main ways of giving students such experiences, laboratory teaching, is met with many challenges such as budget cuts, increased use of virtual learning, and currently the university lockdowns due to the COVID-19 pandemic. We highlight how at-home do-it-yourself (DIY) experiments can be a good way to include physical interaction with your study organism, system, or technique to give the students a practical, authentic learning experience. We hope that by outlining the benefits of a practical, at-home, DIY experiment we can inspire more people to design these teaching activities in the current remote teaching situation and beyond. By contributing two examples in the field of plant biology we enrich the database on experiments to draw inspiration from for these teaching methods