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Autumn

Fig. 10.3. (A) Changes in the percentage of dormant, non-dormant and dead seeds in the seed bank of H. sosnowskyi (empty bars) during the course of a year. Samples were taken in autumn (after seed release), spring (before germination) and summer (before new seeds are shed). Mean values shown are pooled across three localities in Lithuania. (B) Changes in the percentage of living seeds that are not dormant, and of the total seeds that are living for H. sosnowskyi (empty symbols). The percentage of non-dormant seeds is the same in autumn and spring, and decreases to a low value in summer, after the vast majority of non-dormant seed germinated in spring. The percentage of living seed is highest in spring and lowest in summer. Germinated seeds were considered as non-dormant; non-germinated seeds were tested for viability by staining with tetrazolium; viable seeds were considered as dormant. Corresponding data on H. mantegazzianum (Hm; black symbols and bars, respectively) are taken from Krinke et al. (2005).

Fig. 10.3. (A) Changes in the percentage of dormant, non-dormant and dead seeds in the seed bank of H. sosnowskyi (empty bars) during the course of a year. Samples were taken in autumn (after seed release), spring (before germination) and summer (before new seeds are shed). Mean values shown are pooled across three localities in Lithuania. (B) Changes in the percentage of living seeds that are not dormant, and of the total seeds that are living for H. sosnowskyi (empty symbols). The percentage of non-dormant seeds is the same in autumn and spring, and decreases to a low value in summer, after the vast majority of non-dormant seed germinated in spring. The percentage of living seed is highest in spring and lowest in summer. Germinated seeds were considered as non-dormant; non-germinated seeds were tested for viability by staining with tetrazolium; viable seeds were considered as dormant. Corresponding data on H. mantegazzianum (Hm; black symbols and bars, respectively) are taken from Krinke et al. (2005).

both species in the experimental garden of the Institute of Botany, Pruhonice, Czech Republic (50° 00' 03.9" N, 14° 33' 31.7" E). Seeds of H. sosnowskyi were placed in bags made of a fine mesh and buried to a depth of 5-7 cm in the autumn of 2004, those of H. mantegazzianum 2 years earlier, and removed at monthly intervals (except during the winter months when the soil was frozen). Living seeds were classified as non-dormant if they germinated

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- - □ Germinated in laboratory = nondormant Dormant

- - □ Germinated in laboratory = nondormant Dormant

Fig. 10.4. Seasonal pattern in the depletion of the H. sosnowskyi seed bank during the course of one season. Percentages of the seeds buried in the experimental garden of the Institute of Botany, Pruhonice, Czech Republic that were dormant and non-dormant are shown. Each percentage is based on five replicates. Seeds collected earlier in 2004 were buried at a depth of 5-8 cm at the end of October and followed until December 2005. They were taken from the soil every month, except when the soil was frozen, and those that germinated were recorded; those that did not were tested for dormancy by germinating them in the laboratory at 10/5°C and for viability using tetrazolium.

Fig. 10.4. Seasonal pattern in the depletion of the H. sosnowskyi seed bank during the course of one season. Percentages of the seeds buried in the experimental garden of the Institute of Botany, Pruhonice, Czech Republic that were dormant and non-dormant are shown. Each percentage is based on five replicates. Seeds collected earlier in 2004 were buried at a depth of 5-8 cm at the end of October and followed until December 2005. They were taken from the soil every month, except when the soil was frozen, and those that germinated were recorded; those that did not were tested for dormancy by germinating them in the laboratory at 10/5°C and for viability using tetrazolium.

within 1 month following transfer to a climate chamber, or dormant after testing for viability using tetrazolium staining (Baskin and Baskin, 1998).

Of seeds of H. sosnowskyi in the first spring sample (March 2005), 95.2% had already germinated or decayed in the soil. This sample contained a very small proportion of non-dormant and dormant seed, which was ascertained in the laboratory. By May and July, only 3.2% and 1.6%, respectively, of the seeds in the soil had not germinated and all were dormant. From August onwards the soil samples did not contain any living seeds (Fig. 10.4; cf. H. mantegazzianum, see Fig. 5.5). These results suggest that seeds of H. sosnowskyi are unable to survive for more than one season; the seed bank was very quickly depleted by rapid germination in spring and later on by the rapid decay of dormant seeds.

In contrast, at least a small amount of H. mantegazzianum seeds remained viable for considerably longer, a minimum of 3 years (1.2%, see Moravcova et al., Chapter 5, this volume). This may be linked to the fact that a higher percentage of H. mantegazzianum seeds is located in soil layers deeper than 5 cm. The difference is rather small (5% compared to 2% in H. sosnowskyi), but given the fecundity of both species and the fact that the percentage of seeds that survive is generally very low, it may be important. The more seeds that occur in the lower soil layers, the higher the probability of a persistent seed bank (sensu Thompson et al., 1997).

Further indication that the dynamics of both species' seed banks differ is the easier breaking of dormancy in H. sosnowskyi, which enables this species to germinate in autumn when climatic conditions are favourable; however, the survival of seedlings that emerge in autumn and their role in the population dynamics and renewal are unclear; no seedlings were found in the field in Lithuania (Z. GudZinskas, unpublished). The seed bank of H. mantegaz-zianum is classified as 'short-term persistent' (see Moravcovâ et al., Chapter 5, this volume; Krinke et al., 2005), but that of H. sosnowskyi, based on the results of this study, must be considered to be 'transient' (in sense of Thompson et al., 1997). This is suggested despite the relatively high percentage of dormant seeds in Lithuania in summer, which is a feature of short-term persistent seed banks. Nevertheless, other field results (very high percentage of the seeds in the upper soil layer) together with those obtained in the common garden experiment (seeds lost dormancy very rapidly and did not survive more than one season) and germination studies (seeds germinate even more readily than those of H. mantegazzianum) indicate that H. sosnowskyi has a transient soil seed bank. However, to verify this, seed bank experiments in those regions of Europe where the species is invasive (see Jahodovâ et al., Chapter 1, this volume; Nielsen et al., 2005) and the climate is different from Central Europe are needed.

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