Abstract
Abstract Macrophyte species and trait assemblages from 104 minimally disturbed boreal forest lakes, covering broad environmental and geographic gradients were analysed to identify associations with environmental variables at different spatial scales: geographic context (GEO) and catchment (CATCH) and lake (LOCAL) characteristics. Constrained ordination and variation partitioning were used to quantify variation in species (canonical correspondence analysis [CCA] and pCCA) and trait (redundancy analysis [RDA] and pRDA) compositions that could be explained by environmental variables, and to rank the main environmental factors associated with spatial and temporal patterns. Diversity and assemblage composition correlated with spatial context and variables related to the length of the growing season, catchment forest type and with lake characteristics such as ecosystem size, lake productivity and alkalinity. Variation partitioning showed that lake characteristics alone explained 53% (species) and 73.5% (traits) of the variability in macrophyte assemblages. Contrary to predictions, the shared variance component between latitude and catchment forest type (GEO&CATCH < 0.1% for both species and traits) and between latitude and lake characteristics (GEO&LOCAL = 6.7% for species and 3.9% for traits) was low. Temporal variability, measured as changes in species richness, diversity and a pollution‐specific index (the Trophic Macrophyte Index), using a subset of the lakes sampled on two occasions (19 lakes sampled in 2012 and 2018 and five lakes sampled in 2013 and 2019) did not differ (p > 0.05, paired t‐test). Ordination showed that among‐year variability in macrophyte assemblage composition was also negligible (0.3%) compared to the variability explained by GEO, CATCH and LOCAL variables. Combined, these findings indicate low species turnover in the boreal lakes of our study. Responses of macrophyte species and trait assemblages and the TMI index were predictable and significantly correlated with lake characteristics associated with nutrient enrichment (Chl a, nutrients) and alkalinity supporting their use in monitoring eutrophication of boreal lakes.
Highlights
Understanding how patterns and changes in biodiversity relate to local and regional environmental variables has been at the forefront of ecological research for decades (García-Girón et al, 2020; Gaston, 2000)
Constrained ordination and variation partitioning were used to quantify variation in species and trait compositions that could be explained by environmental variables, and to rank the main environmental factors associated with spatial and temporal patterns
Natural variables associated with local patterns of lake biodiversity may be related to species sorting processes associated with catchment land cover, ecosystem size and productivity, while regional patterns are often associated with climate and geology (Heino et al, 2009; Stendera et al, 2012)
Summary
Understanding how patterns and changes in biodiversity relate to local and regional environmental variables has been at the forefront of ecological research for decades (García-Girón et al, 2020; Gaston, 2000). Eutrophication often results in biodiversity loss and lower abundances of submerged species due to light limitation, resulting in a shift in primary production from littoral to pelagic habitats (Jupp & Spence, 1977; Lachavanne et al, 1992; Sand-Jensen et al, 2008) In deeper lakes, their functional importance depends more on intrinsic in-lake characteristics that affect population growth and abundance, such as lake morphometry, depth and light conditions (Jeppesen et al, 1997; Moss, 1990; Søndergaard et al, 2010). Given the relatively slow turnover time of macrophyte assemblages (Dittrich et al, 2016), we determine whether species richness, diversity, assemblage composition and TMI have changed between two six-year sampling events
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