Ruhland C T., Day T A.
Department of Plant Biology, Box 871601, Arizona State University, 85287-1601, Tempe, AZ, USA
Environ Exp Bot. 2001 Apr;45(2):143-154. doi: 10.1016/s0098-8472(00)00089-7.
Populations of Colobanthus quitensis and Deschampsia antarctica, the only two vascular plant species native to Antarctica, are increasing. We performed a seed bank assay to determine the persistence of seeds from intact vegetation/soil cores collected near Palmer Station on the west coast of the Antarctic Peninsula. Vegetation/soil cores were cold stratified at 3 degrees C for >4 years. Subsequent seed bank densities, estimated from seedlings germinated, averaged 847 and 5645 seedlings m(-2) for C. quitensis and D. antarctica, respectively. We also conducted germination trials on C. quitensis seeds collected at our field site and stored for either 120 days or >4 years at 3 degrees C. Germination rates ranged from 6% after 120 days of cold storage to 38% after >4 years of cold storage. These findings show that previous estimates of seed bank densities and germination rates in these species, based on short-term laboratory stratification experiments, may underestimate those found in the field. Stratospheric ozone depletion has lead to increases in ultraviolet-B radiation (UV-B; 280-320 nm) along the Antarctic Peninsula during the austral spring. In a separate experiment we manipulated levels of biologically effective UV-B (UV-B(BE)), over current-year C. quitensis seedlings near Palmer Station on the west coast of the Antarctic Peninsula by placing frames over them that either held filters that absorbed most UV-B(BE) ('reduced UV-B(BE)'), transmitted most UV-B(BE) ('near-ambient UV-B(BE)') or had no filters ('ambient UV-B(BE)'). We monitored seedling survivorship over the course of the growing season (January-March) and growth and pigment concentrations at the end of the season. There were no UV-B(BE) treatment effects on seedling survivorship over the course of the season and overwinter survivorship averaged 12%. However, seedlings growing under near-ambient and ambient UV-B(BE) had 25 and 48% smaller total leaf areas, 7 and 16% fewer leaves and 65 and 82% fewer branches, respectively, than those growing under reduced UV-B(BE). In addition, concentrations of methanol-soluble UV-B-absorbing compounds were 26% higher and concentrations of chlorophyll b were 26% lower in leaves of seedlings growing under ambient UV-B(BE) compared with those under reduced UV-B(BE).
南极洲仅有的两种本土维管植物——南极漆姑草（Colobanthus quitensis）和南极发草（Deschampsia antarctica）的种群数量正在增加。我们进行了一项种子库分析，以确定从南极半岛西海岸帕尔默站附近采集的完整植被/土壤核心样本中的种子的持久性。植被/土壤核心样本在3摄氏度下进行冷分层处理超过4年。随后，根据发芽的幼苗估算出的种子库密度，南极漆姑草和南极发草的平均密度分别为每平方米847株和5645株幼苗。我们还对在野外采集并在3摄氏度下储存120天或超过4年的南极漆姑草种子进行了发芽试验。发芽率从冷藏120天后的6%到冷藏超过4年后的38%不等。这些发现表明，基于短期实验室分层实验对这些物种种子库密度和发芽率的先前估计，可能低估了在野外发现的数值。平流层臭氧消耗导致南极半岛春季期间紫外线B辐射（UV-B；280 - 320纳米）增加。在另一项实验中，我们通过在南极半岛西海岸帕尔默站附近的当年生南极漆姑草幼苗上方放置框架来控制生物有效紫外线B（UV-B(BE)）水平，这些框架要么装有吸收大部分UV-B(BE)的滤光片（“减少UV-B(BE)”），要么透射大部分UV-B(BE)（“接近环境UV-B(BE)”），要么没有滤光片（“环境UV-B(BE)”）。我们在生长季节（1月至3月）监测了幼苗的存活率，并在季节结束时监测了生长情况和色素浓度。在整个季节中，UV-B(BE)处理对幼苗存活率没有影响，越冬存活率平均为12%。然而，与在减少UV-B(BE)条件下生长的幼苗相比，在接近环境和环境UV-B(BE)条件下生长的幼苗总叶面积分别小25%和48%，叶片数量分别少7%和16%，枝条数量分别少65%和82%。此外，与在减少UV-B(BE)条件下生长的幼苗相比，在环境UV-B(BE)条件下生长的幼苗叶片中甲醇溶性紫外线吸收化合物的浓度高26%，叶绿素b的浓度低26%。
