Macrosystem community change in lake phytoplankton and its implications for diversity and function

Aim

We use lake phytoplankton community data to quantify the spatio-temporal and scale-dependent impacts of eutrophication, land-use and climate change on species niches and community assembly processes while accounting for species traits and phylogenetic constraints.

Location

Finland.

Time period

1977–2017.

Major taxa

Phytoplankton.

Methods

We use hierarchical modelling of species communities (HMSC) to model metacommunity trajectories at 853 lakes over four decades of environmental change, including a hierarchical spatial structure to account for scale-dependent processes. Using a “region of common profile” approach, we evaluate compositional changes of species communities and trait profiles and investigate their temporal development.

Results

We demonstrate the emergence of novel and widespread community composition clusters in previously more compositionally homogeneous communities, with cluster-specific community trait profiles, indicating functional differences. A strong phylogenetic signal of species responses to the environment implies similar responses among closely related taxa. Community cluster-specific species prevalence indicates lower taxonomic dispersion within the current dominant clusters compared with the historically dominant cluster and an overall higher prevalence of smaller species sizes within communities. Our findings denote profound spatio-temporal structuring of species co-occurrence patterns and highlight functional differences of lake phytoplankton communities.

Main conclusions

Diverging community trajectories have led to a nationwide reshuffling of lake phytoplankton communities. At regional and national scales, lakes are not single entities but metacommunity hubs in an interconnected waterscape. The assembly mechanisms of phytoplankton communities are strongly structured by spatio-temporal dynamics, which have led to novel community types, but only a minor part of this reshuffling could be linked to temporal environmental change.     

Epiphytic lichen diversity in old-growth and managed Picea abies stands in southern Finland

Abstract. Epiphytic and epixylic lichens were surveyed on 15 1-ha plots in mature Picea abies-dominated boreal forests in southern Finland. The sample plots were classified into three groups according to the age of the dominant tree stand and recent signs of cutting: (1) early mature managed, ‘EM’ (95 -109 yr), (2) late mature managed, ‘LM’ (126 - 145 yr) and (3) old-growth, ‘OG’ (129 - 198 yr). Two data sets on epiphytic and epixylic lichens were recorded from each plot: (1) species on basal trunks and branches of Picea abies and (2) species on all available woody substrates, including basal parts of all tree species, saplings, snags, logs and stumps. 142 epiphytic and epixylic lichen species were found, of which 83 (58%) occurred on P. abies. Mean total numbers of species per sample plot were 69 in EM, 78 in LM and 88 in OG plots, species number on P. abies were 47, 56, and 54 respectively. The LM plots had lower species numbers than OG plots, mainly due to the lack of old Populus tremula trees, but they had higher species number than the EM plots mainly due to the higher age of Picea abies. Differences in species composition, both within and between the three groups, were small. The results suggest that the epiphytic and epixylic lichen diversity in a managed stand can be increased by prolonging the rotation of the stand to >120 yr and by increasing the diversity of habitats in the stand.     

Comparing segmentations by applying randomization techniques

Background  

There exist many segmentation techniques for genomic sequences, and the segmentations can also be based on many different biological features. We show how to evaluate and compare the quality of segmentations obtained by different techniques and alternative biological features.     

The role of metal ions in the activation of arginase.

The role of metal ions as activators of arginase hydrolyzing arginine were studied. The metal ion is assumed to form a complex with arginine and to promote the enzymatic reaction. The activating ability of the metal ion appears to be governed by the chelating ability and/or the coordination numbers which determine whether the metal ion combines with the enzyme or the substrate (or both substrate and enzyme) and factors which influence the configuration of the resulting complexes.