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.