Pollen record of climate change during the last deglaciation from the eastern Tibetan Plateau

showed a relatively high abundance during the late part. Other less dominant shrubs and herbs included Ranunculaceae (0%–12.3%, mean 3.5%), Ephedra (1.2%–6.0%, mean 3.0%), and Chenopodiaceae (1.0%–8.2%, mean 4.8%). Sporadically present taxa in this zone included Poaceae, Caprifoliaceae, Thalictrum, Lamiaceae, Polygonum, Myriophllum, and Caryophylla- ceae. Notably, hydrophilous herb pollen (4.4%–18.0%, mean 10.4%) was dominated by Cyper- aceae (1.6%–16.0%, mean 6.8%) and showed a clear increasing trend over time. Cyperaceae reached 16.0% at 18.0 ka, the highest value in the sequence [Fig 3]. Broad-leaved pollen (20.7%–33.2%, mean 28.2%) was dominated by Quercus and Castanea. The former increased from 4.1% to 14.4% over time with a mean of 9.4%, and the latter attained a relatively high value at the middle of the zone. Betula ranged from 1.5% to 7.3% with a mean of 3.9%. Corylus and Ulmus were frequently present, but in low amounts. Liquidambar occurred occasionally. Conifer pollen (3.3%–13.7%, mean 7.5%) was dominated by Pinus pol- len (2.0%–12.6%, mean 4.1%) and showed a decreasing trend over time. Picea and Abies were present throughout the zone but in low abundance. Fern spores and algae varied in abundance from 4.9% to 13.1% with a mean of 9.7%, show- ing relatively little variation over time [Fig 3]. They were dominated by Pediastrum (1.1%– 8.3%, mean 3.6%) and monolete spores (0.5%–6.7%, mean 3.4%), along with Polypodium (0%–2.5%, mean 1.0%) and trilete spores (0%–4.8%, mean 1.3%). Conentricystis was sporadi- cally present. Zone B (11 samples, 16.8–14.6 ka)

In this zone, the shrub and herb pollen count (59.5%–71.1%, mean 66.1%) was slightly higher than in zone A [Fig 3]. Both Artemisia (8.9%–20.4%, mean 14.1%) and Apiaceae (7.2%–20.7%, mean 12.4%) showed a clear increase over time, along with hydrophilous herb pollen (8.0%– 22.5%, mean 14.7%). Cyperaceae was a dominant type, the abundance varied from 3.0% to 10.2% with a mean of 8.0%. Poaceae (0%–4.2%, mean 1.8%), Polygonum (0%–5.3%, mean 1.4%), Myriophyllum (0.4%–3.7%, mean 2.3%), and Typha (0%–2.9%, mean 1.2%) were fre- quently present but in low abundance [Fig 3]. Despite a clear increase in hydrophilous herb abundance, Cyperaceae decreased significantly between 15.8 and 15.2 ka, with the lowest value at 15.7 ka. Other commonly present shrubs and herbs included Compositae (2.4%–9.5%, mean 4.9%), Chenopodiaceae (1.4%–4.4%, mean 2.9%), Ranunculaceae (2.8%–13.1%, mean 6.9%), Thalictrum (0%-1.9%, mean 0.8%), and Ephedra (1.0%–4.7%, mean 2.7%). Caryophyl- laceae and Lamiaceae occurred sporadically. Broad-leaved tree pollen (21.1%–29.5%, mean 26.0%) showed a small decrease throughout this zone. Quercus (5.9%–14.1%, mean 10.3%), Castanea (4.5%–12.1%, mean 8.4%), and Betula (2.7%–6.5%, mean 3.9%) were less variable than in zone A. Ulmus, Corylus, Liquidambar, and Juglans occurred at low and highly variable percentages. Pinus pollen (1.1%–7.7%, mean 4.2%) was dominant over Abies and Picea (0%–5.2%, mean 2.2%). Fern spores and algae (9.8%–14.6%, mean 12.8%) showed a slight increase in this zone [Fig 3], dominated by Pediastrum (0.9%–7.8%, mean 5.5%) and monolete spores (2.7%–6.7%,

mean 4.5%). Polypodium (0%–2.1%, mean 0.9%) and trilete spores (0%–4.0%, mean 1.6%) were present with low mean values of < 2.0%. Concentricystis was occasionally present. Zone C (15 samples, 14.6–12.9 ka) In zone C, shrub and herb pollen (59.0%–72.1%, mean 64.9%) was dominated by Artemisia (13.0%–23.2%, mean 19.0%), hydrophilous herbs (8.9%–22.8%, mean 15.5%), Apiaceae (6.6%–15.7%, mean 10.9%), Compositae (2.6%–6.8%, mean 4.3%), and Ranunculaceae (2.4%– 9.7%, mean 4.4%), Chenopodiaceae (0%–6.1%, mean 2.6%), and Ephedra (0%–4.5%, mean PLOS ONE Last deglacial pollen reocord from the eastern TP PLOS ONE | https://doi.org/10.1371/journal.pone.0232803 May 6, 2020 6 / 12