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Abstract：
Arctic shrubification is an observable consequence of climate change, already resulting in ecological shifts and global-scale climate feedbacks including changes in land surface albedo and enhanced evapotranspiration. However, the rate at which shrubs can colonize previously glaciated terrain in a warming world is largely unknown. Reconstructions of past vegetation dynamics in conjunction with climate records can provide critical insights into shrubification rates and controls on plant migration, but paleoenvironmental reconstructions based on pollen may be biased by the influx of exotic pollen to tundra settings. Here, we reconstruct past plant communities using sedimentary ancient DNA (sedaDNA), which has a more local source area than pollen. We additionally reconstruct past temperature variability using bacterial cell membrane lipids (branched glycerol dialkyl glycerol tetraethers) and an aquatic productivity indicator (biogenic silica) to evaluate the relative timing of postglacial ecological and climate changes at a lake on southern Baffin Island, Arctic Canada. The sedaDNA record tightly constrains the colonization of dwarf birch (Betula, a thermophilous shrub) to 5.9 ± 0.1 ka, ~3 ka after local deglaciation as determined by cosmogenic 10 Be moraine dating and >2 ka later than Betula pollen is recorded in nearby lake sediment. We then assess the paleovegetation history within the context of summer temperature and find that paleotemperatures were highest prior to 6.3 ka, followed by cooling in the centuries preceding Betula establishment. Together, these molecular proxies reveal that Betula colonization lagged peak summer temperatures, suggesting that inefficient dispersal, rather than climate, may have limited Arctic shrub migration in this region. In addition, these data suggest that pollen-based climate reconstructions from high latitudes, which rely heavily on the presence and abundance of pollen from thermophilous taxa like Betula, can be compromised by both exotic pollen fluxes and vegetation migration lags.
摘要：
北极灌木丛化是气候变化的可观察结果，已经导致生态变化和全球尺度的气候反馈，包括地表反照率的变化和蒸散量的增加。然而,在变暖的世界中，灌木可以在先前冰川化的地形上定居的速度在很大程度上是未知的。结合气候记录对过去的植被动态进行重建可以提供对灌木丛化速率和植物迁移控制的重要见解，但是基于花粉的古环境重建可能会因外来花粉涌入苔原环境而产生偏差。这里,我们使用沉积的古DNA（sedaDNA）重建过去的植物群落，比花粉有更多的局部来源。我们还使用细菌细胞膜脂质（支链甘油二烷基甘油四醚）和水生生产力指标（生物二氧化硅）重建了过去的温度变异性，以评估巴芬岛南部湖泊冰川后生态和气候变化的相对时间，加拿大北极。sedaDNA记录严格限制了矮桦树(Betula，嗜热灌木)至5.9±0.1ka，在附近的湖泊沉积物中，根据宇宙成因10Bemaine测年确定的局部去冰川后〜3ka，并且比Betula花粉晚>2ka。然后，我们在夏季温度的背景下评估古植被历史，发现古温度在6.3ka之前最高，随后在Betula建立之前的几个世纪中冷却。一起,这些分子代理揭示了桦树定殖滞后于夏季的峰值温度，这表明低效的扩散，而不是气候，可能限制了北极灌木在该地区的迁移。此外,这些数据表明，基于花粉的高纬度气候重建，严重依赖来自像桦木这样的嗜热类群的花粉的存在和丰富，外来花粉通量和植被迁移滞后都可能损害。
