Invasion engineering in Antarctica

Human activity and climate change are increasing the
spread of species across the planet, threatening biodiversity and ecosystem
functions. Invasion engineers, such as birds, facilitate plant growth through
manuring of soil, while native vegetation influences plant germination by
creating suitable microhabitats which are especially valuable in cold and dry
polar regions. Here we tested how penguin-derived nitrogen, Antarctic moss
species and warming affect seed germination and
growth of the non-native grass Agrostis
capillaris under laboratory conditions. Experimental settings included a
simulation of contemporary season-specific Antarctic light and temperature (2 °C)
conditions and a +5 °C warming scenario. Mosses (Andreaea depressinervis, A. regularis, Sanionia uncinata and Chorisodontium
aciphyllum) incorporated a range of nitrogen content and
isotopic nitrogen signatures (δ15N) due
to variation in sampling proximity to penguin colonies. Moss species greatly
affected time to germination with consequences for further growth under the
simulated Antarctic conditions. Grass seeds
germinated 10 days earlier among A.
regularis compared to S. uncinata
and C. aciphyllum and 26 days
earlier compared to A. depressinervis. Moss-specific effects are likely
related to microclimatic differences within the moss canopy. Warming reduced
this moss influence. Grass emerged on average 20 days earlier under warming, leading
to increased leaf count (88%), plant height (112%) and biomass (145%). Positive
correlations were identified between moss and grass nitrogen content (r = 0.377),
grass biomass (r = 0.332) and height (r = 0.742) with stronger effects under
the warming scenario. Transfer of nitrogen from moss to grass was confirmed by
δ15N (r = 0.803). Overall, the results suggest a shift from
temperature-limited to N-limited growth of invasive plants under increased
warming in the maritime Antarctic.

人类活动与气候变化正加剧物种在全球范围内的扩散，对生物多样性（biodiversity）与生态系统功能（ecosystem functions）造成威胁。诸如鸟类的入侵型生态系统工程师（invasion engineers）可通过改良土壤促进植物生长；而本土植被则通过构建适宜的微生境影响植物萌发，此类微生境在寒冷干旱的极地地区尤为珍贵。本研究在实验室条件下，测试了企鹅源氮、南极苔藓物种与升温对非本土禾草翦股颖（Agrostis capillaris）的种子萌发与生长的影响。实验设置包含两类情景：一是模拟当代南极季节特异性的光照与温度（2 ℃）条件，二是+5 ℃的升温情景。本次实验所用的苔藓包括凹顶紫萼藓（Andreaea depressinervis）、正则紫萼藓（Andreaea regularis）、镰刀藓（Sanionia uncinata）与尖叶薄齿藓（Chorisodontium aciphyllum）；由于采样点距企鹅群落的远近存在差异，这些苔藓的氮含量与氮同位素特征值（δ¹⁵N）范围各不相同。在模拟的南极环境中，苔藓物种对种子萌发时间具有显著影响，并进一步作用于后续植株生长。相较于镰刀藓与尖叶薄齿藓生境，正则紫萼藓生境下的禾草种子萌发提前10天；而相较于凹顶紫萼藓生境，萌发则提前26天。苔藓的特异性效应可能与苔藓冠层内的微气候差异相关，而升温则削弱了这一苔藓介导的影响。升温条件下，禾草平均提前20天萌发，最终叶片数提升88%、株高提升112%、生物量提升145%。研究发现苔藓与禾草的氮含量（r=0.377）、禾草生物量（r=0.332）及株高（r=0.742）之间存在正相关关系，且在升温情景下该类效应更为显著。通过氮同位素特征值δ¹⁵N分析（r=0.803），证实了氮从苔藓向禾草的转移。总体而言，研究结果表明，在南极海洋性地区，随着升温加剧，入侵植物的生长将从受温度限制转向受氮限制。