Arctic shrub colonization lagged peak postglacial warmth: Molecular evidence in lake sediment from Arctic Canada
Arctic shrub colonization lagged peak postglacial warmth: Molecular evidence in lake sediment from Arctic Canada
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DOI：
10.1111/gcb.14836
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发表时间：
2019-10-11
影响因子：
11.6
通讯作者：
Bunce, Michael
中科院分区：
文献类型：
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作者：
Crump, Sarah E.;Miller, Gifford H.;Bunce, Michael
北极灌木化是气候变化的一个明显后果，已经导致生态变化和全球范围的气候反馈，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，灌木丛在以前的冰川地带定居的速度在很大程度上尚不清楚。结合气候记录重建过去的植被动态可以为灌木化率和植物迁移控制提供重要的见解，但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。在这里，我们利用沉积古 DNA (sedaDNA) 重建了过去的植物群落，它比花粉具有更多的本地来源区域。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）重建过去的温度变化，以评估加拿大北极地区巴芬岛南部一个湖泊冰后生态和气候变化的相对时间。 SedaDNA 记录将矮桦（桦木，一种耐热灌木）的定殖严格限制在 5.9 +/- 0.1 ka，类似于宇宙成因 Be-10 冰碛测年确定的局部冰消之后的 3 ka，并且比附近湖泊沉积物中记录的桦木花粉晚 2 ka。然后，我们评估了夏季气温背景下的古植被历史，发现古气温在 6.3 ka 之前最高，随后在桦木建立之前的几个世纪里变冷。这些分子指标共同揭示了桦木的殖民化滞后于夏季最高气温，这表明低效的扩散，而不是气候，可能限制了该地区北极灌木的迁徙。此外，这些数据表明，高纬度地区基于花粉的气候重建严重依赖于桦木等嗜热类群花粉的存在和丰度，可能会受到外来花粉通量和植被迁移滞后的影响。
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, similar to 3 ka after local deglaciation as determined by cosmogenic Be-10 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.