Huebner Diane Christine, Bret-Harte Marion Syndonia
Department of Biology & Wildlife University of Alaska Fairbanks Fairbanks Alaska.
Institute of Arctic Biology University of Alaska Fairbanks Fairbanks Alaska.
Ecol Evol. 2019 Jan 28;9(4):1880-1897. doi: 10.1002/ece3.4882. eCollection 2019 Feb.
In Low Arctic tundra, thermal erosion of ice-rich permafrost soils (thermokarst) has increased in frequency since the 1980s. Retrogressive thaw slumps (RTS) are thermokarst disturbances forming large open depressions on hillslopes through soil wasting and vegetation displacement. Tall (>0.5 m) deciduous shrubs have been observed in RTS a decade after disturbance. RTS may provide conditions suitable for seedling recruitment, which may contribute to Arctic shrub expansion. We quantified in situ seedling abundance, and size and viability of soil seedbanks in greenhouse trials for two RTS chronosequences near lakes on Alaska's North Slope. We hypothesized recent RTS provide microsites for greater recruitment than mature RTS or undisturbed tundra. We also hypothesized soil seedbanks demonstrate quantity-quality trade-offs; younger seedbanks contain smaller numbers of mostly viable seed that decrease in viability as seed accumulates over time. We found five times as many seedlings in younger RTS as in older RTS, including birch and willow, and no seedlings in undisturbed tundra. Higher seedling counts were associated with bare soil, warmer soils, higher soil available nitrogen, and less plant cover. Seedbank viability was unrelated to size. Older seedbanks were larger at one chronosequence, with no difference in percent germination. At the other chronosequence, germination was lower from older seedbanks but seedbank size was not different. Seedbank germination was positively associated with in situ seedling abundance at one RTS chronosequence, suggesting postdisturbance revegetation from seedbanks. Thermal erosion may be important for recruitment in tundra by providing bare microsites that are warmer, more nutrient-rich, and less vegetated than in undisturbed ground. Differences between two chronosequences in seedbank size, viability, and species composition suggest disturbance interacts with local conditions to form seedbanks. RTS may act as seedling nurseries to benefit many Arctic species as climate changes, particularly those that do not produce persistent seed.
在北极低地冻原，自20世纪80年代以来，富含冰的永久冻土土壤的热侵蚀（热喀斯特）频率有所增加。溯源解冻滑塌（RTS）是热喀斯特扰动，通过土壤侵蚀和植被位移在山坡上形成大型开阔洼地。在扰动十年后的RTS中观察到了高度超过0.5米的落叶灌木。RTS可能提供适合幼苗招募的条件，这可能有助于北极灌木的扩张。我们对阿拉斯加北坡湖泊附近的两个RTS时间序列进行了温室试验，量化了原地幼苗丰度以及土壤种子库的大小和活力。我们假设，与成熟的RTS或未受干扰的冻原相比，近期的RTS为更多的幼苗招募提供了微生境。我们还假设土壤种子库表现出数量-质量权衡；较年轻的种子库包含数量较少但大多具有活力的种子，随着种子随时间积累，其活力会下降。我们发现，较年轻的RTS中的幼苗数量是较老的RTS中的五倍，包括桦树和柳树，而在未受干扰的冻原中没有幼苗。较高的幼苗数量与裸土、较温暖的土壤、较高的土壤有效氮以及较少的植物覆盖有关。种子库活力与大小无关。在一个时间序列中，较老的种子库更大，发芽率没有差异。在另一个时间序列中，较老的种子库发芽率较低，但种子库大小没有差异。在一个RTS时间序列中，种子库发芽率与原地幼苗丰度呈正相关，这表明种子库在干扰后进行了植被恢复。热侵蚀可能通过提供比未受干扰的地面更温暖、营养更丰富且植被更少的裸微生境，对冻原的幼苗招募很重要。两个时间序列在种子库大小、活力和物种组成上的差异表明，干扰与当地条件相互作用形成了种子库。随着气候变化，RTS可能充当幼苗苗圃，使许多北极物种受益，特别是那些不产生持久种子的物种。
