Abstract
Lake sediments represent valuable and widely used archives for tracking environmental and biotic changes over time. Past aquatic communities are traditionally studied via morphological identification of the remains of organisms. However, molecular identification tools, such as DNA metabarcoding, have revolutionized the field of biomonitoring by enabling high-throughput and fast identification of organisms from environmental samples (e.g., sediments and soil). Sedimentary ancient DNA (sedaDNA) metabarcoding, an approach to track the biodiversity of target organisms from sediment cores, spanning thousands of years, has been successfully applied in many studies. However, researchers seldom explore how well the signals from sedaDNA data correlate with the fossil records of target organisms. This information is essential to infer past environmental conditions and community changes of bioindicators when the increasingly popular molecular identification method, metabarcoding, is desired instead of a morphological identification approach. In this study, we explore the correlations of diatom valve records across the last ∼940 years with the diatom sedaDNA metabarcoding data from the same sediment core from lake Nam Co (Tibetan Plateau). Overall, the results from valve vs. sedaDNA data revealed concordant diatom richness as well as community patterns. However, several mismatches in the diatom taxonomic composition existed between the data sets. In general, sedaDNA data harbored much higher diatom diversity, but due to the lack of reference sequences in public databases, many molecular units (amplicon sequence variants) remained unclassified to lower taxonomic levels. As our study lake, Nam Co, is characterized by brackish water and alkaline pH, some likely cases for the observed taxonomic composition mismatches may be due to a valve dissolution issue. Nevertheless, significant drivers for the diatom richness and community structure largely corresponded between data sets. Both valve and sedaDNA data demonstrated similar breakpoints for historical diatom community shifts. A particularly strong shift in the diatom community structure occurred after ∼1950 CE, which may be associated with abrupt environmental changes on the Tibetan Plateau. Altogether, our study indicates that environmentally driven signals reflected by the diatom communities are successfully recovered via microfossil as well as molecular identification methods.
Highlights
Various pieces of information hidden in lake sediments are widely used to infer past environmental conditions over long time periods (Capo et al, 2021)
The comparison of consistency in recovered diatom communities with valves and sedimentary ancient DNA (sedaDNA) data using Procrustes test revealed a significant correlation between the community structures
For the valve data set, the model chosen by the Distance-based linear models (DistLM) analyses identified temperature, grain size proxy (Zr/Rb), Ti, and LOI as the most important variables explaining the variation in diatom community composition
Summary
Various pieces of information hidden in lake sediments are widely used to infer past environmental conditions over long time periods (Capo et al, 2021). Some of the most important clues about the past environment may be obtained through studying community structures of bioindicator organisms These groups of organisms respond quickly to the changes in their environment, indicating the environmental condition of their habitat. The integrity of diatom records in the sediments is a main concern if the fossil assemblages are used to infer paleo-environmental conditions (Flower and Ryves, 2009). The increased salinity and pH potentially favors diatom valve dissolution in the lake sediments (Flower, 1993; Ryves et al, 2001; Ryves et al, 2006), several studies have used diatom fossil assemblages from Tibetan lake sediment cores to infer paleo-environmental conditions (e.g., Wang et al, 2011; Kasper et al, 2013; Laug et al, 2021). Diatom dissolution indices (such as mentioned in Flower and Ryves, 2009) have rarely been calculated to evaluate the integrity of diatom fossil records from Tibetan lake sediment cores. The preservation of diatom valves may largely shape the conclusions made based only on their fossil records (Flower and Ryves, 2009; Smol and Stoermer, 2010)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
