Jan-Erik Thrane

Norwegian Institute for Water Research | NIVA

Aquatic macrophytes recolonised inland waters following the last glacial retreat. The resulting diversity and the variables influencing it remain largely unexplored north of the Arctic Circle, including possible effects of past colonisation routes. Our understanding of species diversity north of the Arctic Circle has also been hampered by a lack of...

Many boreal lakes are experiencing an increase in concentrations of terrestrially derived dissolved organic matter (DOM)-a process commonly labeled "browning." Browning affects microbial and photochemical mineraliza-tion of DOM, and causes increased light attenuation and hence reduced photosynthesis. Consequently, browning regulates lake heterotrop...

Covariation in species richness and community structure across taxonomical groups (cross‐taxon congruence) has practical consequences for the identification of biodiversity surrogates and proxies, as well as theoretical ramifications for understanding the mechanisms maintaining and sustaining biodiversity. We found there to exist a high cross‐taxon...

Acquisition of tolerance to an environmental stressor can result in organisms displaying slower growth after stress release. While well-grounded in the theory, empirical evidence of trade-off between stress tolerance and organism fitness is scarce and blurred by the interaction with different environmental factors. Here, we report the effects of wa...

Concentrations of dissolved organic matter (DOM) are increasing in a large number of lakes across the Northern hemisphere. This browning serves a dual role for biota by protecting against harmful ultraviolet radiation, while also absorbing photosynthetically active radiation. The photochemical activation of DOM and subsequent formation of reactive...

In recent decades, the freshwater alga Gonyostomum semen (Ehrenberg) Diesing has increased in abundance and distribution, which has created problems regarding the use of lakes for drinking water and recreation. Increases in lake dissolved organic carbon (DOC; browning) and climate warming are among current hypotheses that explain the phenomenon of...

Temperature and nutrients are key factors affecting the growth, cell size, and physiology of marine phytoplankton. In the ocean, temperature and nutrient availability often co-vary because temperature drives vertical stratification, which further controls nutrient upwelling. This makes it difficult to disentangle the effects of temperature and nutr...

Results from ANOVA on alkaline phosphatase activity (APA) ANOVA table showing the sum of squares, fraction of variance explained, and p-value for each of the explanatory terms in a linear model with APA as the response variable.

ANOVA tables for cell size ANOVA tables showing the sum of squares (Sum sq), fractions of variance explained (% var), and p-values for the explanatory terms (P-regime, temperature (Temp) and their interaction) in a linear model with mean cell size as the response variable. ANOVAs were done separately for each specie to remove the large variance in...

Responses of cell quota of C, N, P, RNA, C:P and N:P to temperature and P-regime Responses of cell quota of C, N, P, RNA, C:P and N:P to temperature and P-regime. The data are plotted on log-scale. Dots represent P-limited cultures (−P), pluses P-replete cultures (+P). Solid lines are drawn if the difference between temperatures was significantly d...

PERMANOVA table for the variance in cell quota of C, N, P and RNA that was related to species, P-regime, temperature, and the interaction between temperature and P-regime PERMANOVA table for the variance in cell quota of C, N, P and RNA that was related to species, P-regime, temperature, and the interaction between temperature and P-regime. The % o...

Results from linear models of cell quota of C, N, P and RNA Results from linear models of cell quota of C, N, P and RNA. Legend as in Table 2 in manuscript.

Text file with raw data from the experiment Text file containing the raw data from the experiment. Columns contain the follwing data and information: “Species”, denotes which species the data are from; “temp”, the temperature of the experimental unit (13 or 19 degrees C); “P”, the P-regime of the experimental unit (“ P +”, nutrient replete turbidos...

PCA plot based on log-transformed and standardized cell quota of C, N, P, and RNA in the 36 experimental units PCA plot based on log-transformed and standardized cell quota of C, N, P, and RNA in the 36 experimental units. Due to the factorial design consisting of three species, two temperatures, and two P-regimes, we obtained 12 unique experimenta...

Alkaline phosphatase activity Alkaline phosphatase activity (APA) plotted as a function of P-regime (P + is nutrient replete cultures, P − is P-limited cultures) given temperature (13 °C and 19 °C) and species.

Cell size vs. temperature and P-regime Mean cell size, calculated as the average equivalent spherical diameter (ESD) from weekly samplings over the >20-week experimental period, in the different treatments and species. Dots represent P-limited cultures (−P), pluses P-replete cultures (+P).

1. Lakes word-wide are in rapid change due to direct or indirect climate impacts. In boreal areas, the increased concentrations of dissolved organic matter (DOM) are profoundly affecting light climate and productivity in multiple ways. Photochemical and microbial mineralization of DOM are major sources of CO2 in these lakes. It has been suggested t...

There is growing empirical and theoretical evidence for a positive relationship between the nitrogen (N)-to-phosphorus (P) ratio of phytoplankton and temperature. However, few have tested how the optimal supply N:P ratio; the dissolved N:P ratio at which nutrient limitation switches from one element to the other, responds to temperature. In this st...

Phytoplankton acclimates to irradiance by regulating the cellular content of light-harvesting complexes, which are nitrogen (N) rich and phosphorus (P) poor. Irradiance is thus hypothesised to influence the cellular N : P ratio and the N : P defining the threshold between N and P limitation (the 'optimal' N : P). We tested this hypothesis by first...

Boreal lakes are important net sources of greenhouse gases (GHGs). In this study we analyzed concentrations of CO2, CH4, N2O as well as O2, N2 and argon (Ar) from the epilimnion of 75 boreal lakes covering gradients in total organic carbon (TOC), phosphorus (P) and nitrogen (N) deposition. The Ar-corrected gas saturation deficit was used as a proxy...

The Gauss-peak spectra (GPS) method represents individual pigment spectra as weighted sums of Gaussian functions, and uses these to model absorbance spectra of phytoplankton pigment mixtures. We here present several improvements for this type of methodology, including adaptation to plate reader technology and efficient model fitting by open source...

Colored dissolved organic matter (CDOM) absorbs a substantial fraction of photosynthetically active radiation (PAR) in boreal lakes. However, few studies have systematically estimated how this light absorption influences pelagic primary productivity. In this study, 75 boreal lakes spanning wide and orthogonal gradients in dissolved organic carbon (...