annua clumps might have interfered with the assumed seed rain and our interpretation of results might have been biased. The selected scheme potentially allowed to minimize the interference of seed rain of plants growing in the vicinity. At each sampling point we collected 100 cm3 of soil from the 0–5 cm layer. We collected 80 soil samples amounting to 8 liters and 0.157 m2 VX-689 chemical structure soil surface area. The collected samples were air dried at room temperature at the Station and transported to our laboratory in Poland at 4 °C. Fig. 1 Sampling scheme. C, N, WSW, ESE—soil sample location in relation to tussock position Fig. 2 Poa

annua in the vicinity of Arctowski Station We sieved the samples through 0.5 and 1.5 mm sieves and extracted caryopses from the 0.5–1.5 mm soil fraction under a stereoscopic microscope. Extracted caryopses and the remaining soil were placed in a germination chamber for 3 months under 12 h photoperiod, 10/23 °C. These optimal germination

conditions were used to promote germination in all seeds with potential germination capability and therefore to assess the size of the soil seed bank of living diaspores. Under Antarctic conditions these seeds would have remained a part of a living soil seed bank with the potential ability to germinate when conditions become adequate. Thus we assessed the size of the soil seed bank with the NVP-AUY922 extraction method and the germination method. At the same time we estimated the Napabucasin germination capacity of seeds by germination tests of seeds extracted from soil samples. We assumed that seeds which failed to germinate were not viable. To calculate seed densities per square meter we divided the seed count in a sample by the area of the sample (Baskin and Baskin 2001). We used nonparametric statistics, as the distribution of seeds in samples

was not normal. We used the sign test to compare the seed bank size assessed with the extraction and germination methods for samples from the center point. With Spearman correlation we checked the relation between the tussock diameter and Suplatast tosilate height and the size of the seed bank, as well as the relation between the size of the seed bank estimated with the extraction and germination methods. We performed Friedman’s ANOVA to check for differences between sampling points around the clump. The analysis was performed with SAS 9.2 (SAS Institute Inc. 2007) and Statistica 9.0 (StatSoft and 2009). Results Altogether we extracted 520 P. annua caryopses. This corresponds to 3,312 seeds m−2. Out of all extracted seeds, 426 germinated, which is nearly 82 %. Additionally, 43 seeds germinated from samples left after the propagule extraction, therefore altogether 469 seeds germinated from the collected soil samples. Thus, the size of P. annua seed bank surrounding the tussocks assessed with the germination method corresponded to 2,986 seeds m−2.