Response of Polytrichum strictum Plants to Regional Warming of the Antarctic Peninsula Using Geochemistry of Past and Modern and Fossil Plants

Abstract

Ecosystems of the western Antarctic Peninsula (AP) are currently experiencing one of the fastest rates of regional warming in the world. Aerobic moss-dominated peatbanks, which have the most flourishing vegetation in this ice-dominated region, were studied along the wAP to investigate plant growth conditions over space and time. Living plants of the dominant moss bank species, Polytrichum strictum, were collected from 13 populations along seven sites located between 6409' and 6735'S and a core was raised from a Polytrichum-dominated moss bank at 6514’S. Stable isotope ratios were measured in modern and fossil plant tissue. Modern plant δ 13C values varied from −31.7 to −27.0‰ and were influenced more by tissue type than geographic location. Modern plant δ 15N values ranged from −1.4 to +14.7‰ showing little tissue effect. In the core, radiocarbon-dated fossil leaf tissue showed plant growth began 2300 years ago (one of the oldest plant ages on the wAP), peat accumulation rates varied over time, and there is evidence for a hiatus between ~1600 and 800 years ago BP. Fossil leaves deposited during recent decades had δ13C values between −30.3 and −27.2‰ that were 2.0‰ more depleted than any time during the last 2300 years. Enriched δ15N values of +11.5 to +13.2‰ in fossil leaves deposited between 209 and 700 years before present (BP) suggest a period of more trophically-enriched animal inputs. Our results suggest P. strictum plants have experienced unprecedented growth conditions with recent rapid warming and that moss bank ecosystems may have changed nutrient sources over time.