Snow-vegetation-atmosphere interactions in alpine tundra

The interannual variability of snow cover in alpine areas is increasing, which may affect the tightly coupled cycles of carbon and water through snow-vegetation-atmosphere interactions across a range of spatio-temporal scales. To explore the role of snow cover for the land-atmosphere exchange of CO2 and water vapor in alpine tundra ecosystems, we combined three years (2019&ndash;2021) of continuous eddy covariance flux measurements of net ecosystem exchange of CO2 (NEE) and evapotranspiration (ET) from the Finse site in alpine Norway (1210 m a.s.l.) with a ground-based ecosystem-type classification and satellite imagery from Sentinel-2, Landsat 8, and MODIS. While the snow conditions in 2019 and 2021 can be described as site-typical, 2020 features an extreme snow accumulation associated with a strong negative phase of the Scandinavian Pattern of the synoptic atmospheric circulation during spring. This extreme snow accumulation caused a one-month delay in melt-out date, which falls on the 92nd-percentile in the distribution of yearly melt-out dates in the period 2001&ndash;2021. The melt-out dates follow a consistent fine-scale spatial relationship with ecosystem types across years. Mountain and lichen heathlands melt out more heterogeneously than fens and flood plains, while late snowbeds melt out up to one month later than the other ecosystem types. While the summertime average Normalized Difference Vegetation Index (NDVI) was reduced considerably during the extreme snow year 2020, it reached the same maximum as in the other years for all but one the ecosystem type (late snowbeds), indicating that the delayed onset of vegetation growth is compensated to the same maximum productivity. Eddy covariance estimates of NEE and ET are gap-filled separately for two wind sectors using a random forest regression model to account for complex and nonlinear ecohydrological interactions. While the two wind sectors differ markedly in vegetation composition and flux magnitudes, their flux response is controlled by the same drivers as estimated by the predictor importance of the random forest model as well as the high correlation of flux magnitudes (correlation coefficient r = 0.92 for NEE and r = 0.89 for ET) between both areas. The one-month delay of the start of the snow-free season in 2020 reduced the total annual ET by 50 % compared to 2019 and 2021, and reduced the growing season carbon assimilation to turn the ecosystem from a moderate annual carbon sink (&minus;31 to &minus;6 gC m&minus;2 yr&minus;1) to a source (34 to 20 gC m&minus;2 yr&minus;1). These results underpin the strong dependence of ecosystem structure and functioning on snow dynamics, whose anomalies can result in important ecological extreme events for alpine ecosystems.</p

Climate–ecosystem modelling made easy: The Land Sites Platform

Dynamic Global Vegetation Models (DGVMs) provide a state-of-the-art process-based approach to study the complex interplay between vegetation and its physical environment. For example, they help to predict how terrestrial plants interact with climate, soils, disturbance and competition for resources. We argue that there is untapped potential for the use of DGVMs in ecological and ecophysiological research. One fundamental barrier to realize this potential is that many researchers with relevant expertize (ecology, plant physiology, soil science, etc.) lack access to the technical resources or awareness of the research potential of DGVMs. Here we present the Land Sites Platform (LSP): new software that facilitates single-site simulations with the Functionally Assembled Terrestrial Ecosystem Simulator, an advanced DGVM coupled with the Community Land Model. The LSP includes a Graphical User Interface and an Application Programming Interface, which improve the user experience and lower the technical thresholds for installing these model architectures and setting up model experiments. The software is distributed via version-controlled containers; researchers and students can run simulations directly on their personal computers or servers, with relatively low hardware requirements, and on different operating systems. Version 1.0 of the LSP supports site-level simulations. We provide input data for 20 established geo-ecological observation sites in Norway and workflows to add generic sites from public global datasets. The LSP makes standard model experiments with default data easily achievable (e.g., for educational or introductory purposes) while retaining flexibility for more advanced scientific uses. We further provide tools to visualize the model input and output, including simple examples to relate predictions to local observations. The LSP improves access to land surface and DGVM modelling as a building block of community cyberinfrastructure that may inspire new avenues for mechanistic ecosystem research across disciplines.publishedVersio

Daylength influences the response of three clover species (Trifolium spp.) to short-term ozone stress

-Long photoperiods characteristic of summers at high latitudes can increase ozone-induced foliar injury in subterranean clover (Trifolium subterraneum) This study compared the effects of long photoperiods on ozone injury in red and white clover cultivars adapted to shorter or longer daylengths of southern or northern Fennoscandia. Plants were exposed to 70 ppb ozone for six hours during the daytime for three consecutive days. Simultaneously, the daylength in the growth rooms was altered to long-day (10 h light; 14 h dim light) and short-day (10 h light; 14 h darkness) conditions. Thermal imaging showed that ozone disrupted leaf temperature and stomatal function, particularly in sensitive species, in which leaf temperature deviations persisted for several days after ozone exposure. Longday conditions increased visible foliar injury (30%–70%), characterized by chlorotic and necrotic areas, relative to short day conditions in all species and cultivars independently of the photoperiod in the region they were adapted to

Leaf mottling/variegation and shape in the Ledebouria revoluta complex ? Development, stability and putative function

The aims of this paper are three-fold: 1. To analyse the development and stability in vegetative traits such as leaf shape, growth and pigmentation patterns in three different morphotypes (defined by leaf shape and pigmentation) of the Ledebouria revoluta complex. 2. To discuss the putative function of leaf mottling/variegation. 3. To discuss plasticity in these traits in relation to taxonomy and species delimitation within the complex. Clones were analysed in a cultivation experiment with two nitrogen levels (N1 and N2), three morphotypes (A, B & C) and two light levels (L1 and L2). Anthocyanins were found in hypodermal cells, particularly in the proximal (i.e. young) parts of the leaf. The red pigmentation faded out in distal (i.e. more mature) parts of the leaf. Furthermore, older, outer leaves had more pigmentation than younger, inner leaves. Increased nitrogen availability had no effect on leaf pigmentation. Some plants developed significantly more red pigmentation adaxially at high light intensities, whereas abaxial pigmentation was unaffected by light intensity. The pigmentation of the two sides of a leaf therefore seems to be regulated independently and may accordingly serve different functions for the plants. Adaxial pigmentation (mainly in the form of mottling, pigmentation mainly in spots) may serve as photoprotection, whereas abaxial pigmentation (mainly in the form of variegation, pigmentation mainly in bands) may possibly be aposematic. In the field a high degree of intrapopulational variation in pigmentation patterns was observed. This might be due to local habitat heterogeneity and gene flow or frequency dependent selection. Characters relevant to taxonomy (leaf shape, pigmentation pattern) only changed to a limited extent, suggesting that the vegetative traits are genetically based. The three different morphotypes were easily recognized unrelated to the different treatments. Whether a formal taxonomic status is justified for the different morphotypes will need more plant material and genetic data and cannot be decided based on this study

Forslag til norsk overvåkingsnettverk for å oppfylle NEC‐direktivets krav om å overvåke effekter av luftforurensing

Norge har et eksisterende overvåkingsnettverk for å måle effekter av luftforurensninger som forsuring, overgjødsling og ozoneksponering i økosystemer. Ved eventuell implementering av nytt NEC‐direktiv «takdirektiv» (2016/2284/EU) må Norge rapportere inn overvåkingsnettverk og resultater fra overvåking av effekter av luftforurensninger i økosystemer. I denne rapporten er dagens overvåkingsnettverk vurdert med hensyn til de krav som stilles i nytt NEC‐direktiv. Resultater viste at for innsjøer og elver er dagens overvåkingsnettverk relatert til forsuring tilfredsstillende. For overgjødsling av skog, skogsjord og terrestrisk natur er det behov for oppgraderinger av overvåkingsnettverket. I forhold til ozonskader i vegetasjon er det behov for oppgraderinger av dagens overvåkingsnettverk. Det vil påløpe kostnader for opprettelse av nye overvåkingsstasjoner og oppgraderinger av dagens overvåkingsnettverk. Estimerte kostnader for å dekke mangler i eksisterende overvåkingsnettverk er angitt i rapporten

Disentangling effects of natural and anthropogenic drivers on forest net ecosystem production

Net Ecosystem Production (NEP) of forests is the net carbon dioxide (CO₂) fluxes between land and the atmosphere due to forests' biogeochemical processes. NEP varies with natural drivers such as precipitation, air temperature, solar radiation, plant functional type (PFT), and soil texture, which affect the gross primary production and ecosystem respiration, and thus the net C sequestration. It is also known that deposition of sulphur and nitrogen influences NEP in forest ecosystems. These drivers' respective, unique effects on NEP, however, are often difficult to be individually identified by conventional bivariate analysis. Here we show that by analyzing 22 forest sites with 231 site-year data acquired from FLUXNET database across Europe for the years 2000–2014, the individual, unique effects of these drivers on annual forest CO₂ fluxes can be disentangled using Generalized Additive Models (GAM) for nonlinear regression analysis. We show that S and N deposition have substantial impacts on NEP, where S deposition above 5 kg S ha−¹ yr−¹ can significantly reduce NEP, and N deposition around 22 kg N ha−¹ yr−¹ has the highest positive effect on NEP. Our results suggest that air quality management of S and N is crucial for maintaining healthy biogeochemical functions of forests to mitigate climate change. Furthermore, the empirical models we developed for estimating NEP of forests can serve as a forest management tool in the context of climate change mitigation. Potential applications include the assessment of forest carbon fluxes in the REDD+ framework of the UNFCCC.ISSN:0048-9697ISSN:1879-102

Daylength influences the response of three clover species (Trifolium spp.) to short-term ozone stress

-Long photoperiods characteristic of summers at high latitudes can increase ozone-induced foliar injury in subterranean clover (Trifolium subterraneum) This study compared the effects of long photoperiods on ozone injury in red and white clover cultivars adapted to shorter or longer daylengths of southern or northern Fennoscandia. Plants were exposed to 70 ppb ozone for six hours during the daytime for three consecutive days. Simultaneously, the daylength in the growth rooms was altered to long-day (10 h light; 14 h dim light) and short-day (10 h light; 14 h darkness) conditions. Thermal imaging showed that ozone disrupted leaf temperature and stomatal function, particularly in sensitive species, in which leaf temperature deviations persisted for several days after ozone exposure. Longday conditions increased visible foliar injury (30%–70%), characterized by chlorotic and necrotic areas, relative to short day conditions in all species and cultivars independently of the photoperiod in the region they were adapted to