The thesis at hand dealt with the topic of preservation of calcareous grasslands by comprising various aspects, which range from phylogeographic research to seed science. The aim of this thesis was to elucidate the origins of rare and threatened calcareous grasslands species and to provide tools for a successful conservation of biodiversity via seeds.
Chapter 1 presented an introduction by reporting on threatened and endangered landscapes in Germany, the current conservation status of calcareous grasslands, their known restoration potential and provided knowledge about the origin of calcareous grassland species. Moreover the issue of ex situ conservation via seed banks was addressed, detailing important subjects of seed science such as seed morphology, germination and dormancy, viability and longevity. The aims of all chapters were listed and the used scientific approaches were explained.
Chapter 2 focused on the postglacial spread of a common calcareous grassland species, Sanguisorba minor Scop., to Central Europe. Furthermore, seed morphology was included, as it is the main determinant of subspecies of the morphologically extremely variable species. To achieve these objectives, leaf and seed material from 38 populations throughout Europe were collected and examined in a two-step analysis. Firstly, the spatial genetic structure was investigated via AFLP and secondly, the findings were combined with the seed morphology.
The phylogeographic analysis revealed a distinct separation of eastern and western lineages and rare markers pointed towards a traditional southern but also a potential northern refugia. Genetic similarity between south-eastern and south-western subsp. balearica populations was lower than between northern subsp. minor and south-western subsp. balearica populations. It was concluded that S. minor recolonized Central Europe from Iberia or northern glacial refugia in France, Belgium or Germany. The present situation of the subspecies depicts either incomplete lineage sorting or the existence of secondary hybrid zones, which is differently expressed in neutral marker and morphological differentiation.
In Chapter 3 seed traits associated with seed ageing and ex situ storage and their prospects for ex situ conservation were evaluated. Seeds of 39 calcareous grassland species were collected and the seed longevity was determined by artificially ageing under rapid ageing conditions. The results showed that the seed longevity values strongly varied. Physical dormancy and endosperm absence had significantly positive effects and physiological dormancy was negatively correlated with seed longevity. Seed mass, seed shape and seed coat thickness were not associated with longevity. Calcareous grassland species therefore do not solely rely on seed longevity for long-term persistence and regeneration. The influence of physical dormancy and endosperm presence were discussed with regard to the evolution from endospermic to non-endospermic seeds. Low seed longevity of physiologically dormant seeds was explained by the lack of germination specific antioxidants that otherwise counteract oxidative damages in non-dormant aged seeds.
Chapter 4 addressed the question whether seed longevity of calcareous grassland species in the soil and in ex situ storage are correlated. Therefore, longevity information gained from artificial ageing trials was compared with soil seed bank persistence on the basis of soil seed bank persistence categories of (Poschlod et al., 1998) and the longevity index LI of Thompson et al. (1997). For three-quarter of the surveyed species soil seed bank persistence and survival of artificially aged seeds were correlated, which was explained by an inherent species-specific seed longevity. Regarding seed traits, a correlation with endosperm presence and physiological dormancy was confirmed for soil seed bank persistence. Remaining contradictory results of species with long-lived soil seed banks but low survival at artificial ageing and vice versa were interpreted with unpredictable effects that operate on seeds in the soil like germination, seed regeneration by wet-dry cycling, predation and the seed size-seed number trade-off, which may cover the actual inherent longevity.
In Chapter 5 the assessment of seed viability via X-ray was investigated. X-rays provide information about the internal structures of a seed and therefore show promise for detection of viability and even germination capacity without destroying valuable seeds. Combined germination-Tetrazolium tests and X-ray images of 176 wild flowering plant species from 207 accessions were compared in order to examine the efficiency of X-ray analysis to detect viability. The comparison revealed a strong analogy of viability determination of both methods. Whereas the evaluation of little/non-endospermic seeds gave approximately same results, endospermic seed evaluation differed. Therefore especially for non/little endospermic seeds X-ray analysis can provide a useful and quick tool for viability detection and prediction of germinability, whereas for endospermic seeds additional research is needed.
Chapter 6 summarized the gained results with regard to ex situ and in situ seed dispersal in space and time. Seeds have contributed the most to species current geographical distribution (dispersal in space). It was pointed out that for calcareous grassland species such as S. minor long distance seed dispersal by domestic animals are of importance for colonization. Even during the LGM, contiguous European human populations extended from central France to the lowlands in Southern Germany and to Eastern Europe and may have caused direct and indirect carriage of S. minor. It was suggested that the discovered northern refugia of S. minor might be of importance as a source for future safeguarding calcareous grassland species. Due to present-day limited dispersal in space, it was postulated that at least dispersal in time needed to be guaranteed by integrative strategies. Maintaining genepools on site but additionally preserve viable seeds in seed banks was proposed to be necessary to safeguard calcareous grasslands plant inventory and improve the success of restoration efforts. In the following the relevance of seed traits for calcareous grassland conservation (dispersal in time) was discussed. The importance of the seed trait “endosperm presence” for ecological studies was emphasized as it points towards seed longevity and provides information about the feasibility of quick viability assessment via X-ray analysis
