Perspectives
Assemblages of diatom communities reflect environmental parameters
(Dixit, Smol, Kingston & Charles 1992), and therefore they are widely
used as paleo-ecological indicators of lake ecosystems (Douglas & Smol
2010). We found that the diatom communities within sediment samples from
Nam Co can be related to the same environmental variables for both, the
morphological and metabarcoding data sets, which is in accordance with
the study by Dulias, Stoof-Leichsenring, Pestryakova and Herzschuh
(2017). This suggests that inferring (paleo-) environmental
characteristics via, for example, diatom-based transfer functions would
produce similar results using either method, where the high-throughput
nature of metabarcoding analyses, however, enables simultaneous
processing of much larger numbers of samples in a time-effective manner.
Although not tested here, the additional ‘fine-tuning’ of the
metabarcoding data with e.g. quantification correction factors or
including phylogeny of the OTUs has been suggested to further improve
the (biomass) correlations between microscopy and metabarcoding results
(Vasselon et al. 2018; Mortágua et al. 2019) as well as
boost the applicability of the latter for biomonitoring purposes (Keck,
Vasselon, Rimet, Bouchez & Kahlert 2018). Because of the incompleteness
of available DNA barcode databases, taxonomy-independent methods for
molecular taxa are another promising advancement towards the
applicability of metabarcoding in environmental surveys
(Apotheloz-Perret-Gentil et al. 2017; Tapolczai et al.2019). Moreover, when the preservation of diatom valves is poor, as for
example in saline, high pH lakes with low sediment accumulation rates
(Flower 1993), DNA may still preserve in sediments as for example has
been demonstrated by studying ‘non-fossilizing’ phytoplankton by means
of sedimentary ancient DNA (Li et al. 2016). The strong
similarity of our metabarcoding results from 10 g and 0.5 g of DNA
extracts implies that ‘small’ DNA isolation kits (for
~0.5 g) may serve as an alternative approach when the
amount of sediments is limited in sedimentary ancient DNA (sedaDNA)
studies.