Seed bank assembly in an unmanaged ruderal grassland recovering from long-term exposure to industrial emissions

The main aim of this 3-year study was to relate the temporal patterns in seed bank composition of a ruderal grassland previously subjected to industrial pollution with the successional patterns in the above-ground vegetation. In particular, we tested whether the observed changes conformed to a paradigm of declining seed numbers and diversity and decreasing similarity between seed bank and vegetation, as previously formulated for secondary successions. We found that seed numbers and the number of species per soil sample increased during the 3 years of the study. The compositional similarity between seed bank and vegetation did increase for the 0–2 cm surface layer, and remained roughly constant for deeper soil layers. Thus, the patterns found differed from those of other secondary successional communities and do not support the tested paradigm. Rather, our findings resemble those from a number of primary successional ecosystems. We suggest that temporal patterns of similarity between seed bank and vegetation should be interpreted in terms of the factors that determine the relative rates of compositional change in vegetation and seed bank at different stages of succession. Our study also provides information about the seed bank persistence of 22 species, including several species for which such knowledge previously was scarce. In particular, this study indicates the extreme longevity of the seeds of the halophytic grass Puccinellia distans. Several years after its rapid decline in the vegetation, this species dominated the seed bank, and no measurable decline in seed density was detected during this study.     

Edaphic patchiness influences grassland regeneration from the soil seed‐bank in mountain grasslands of central Argentina

The soil seed‐banks in the main natural vegetation patches that make up mountain grasslands on granite substrates in central Argentina were studied. The main natural vegetation types are moist swards, tall‐tussock grasslands and stony grasslands. Ten compound soil samples from each community at two soil depths (0–5 and 5–10 cm) were taken. The density of soil seed‐banks was highest in moist swards, intermediate in stony grasslands and lowest in tall‐tussock grasslands. Low levels of similarity were found between the established vegetation and total soil seed‐bank in tall‐tussock grasslands and stony grasslands, but the similarity was higher in swards. In all three communities the seed‐bank was most frequently transient in nature. Short‐term persistent and long‐term persistent seed‐banks were less frequent. Regeneration from the seed‐banks after disturbance is expected to differ among communities on different edaphic patches. On the basis of the density and longevity of the soil seed‐banks and the similarity to the established vegetation, potential for in situ regeneration should be lower in tall‐tussock grasslands, intermediate in stony grasslands and higher in moist swards.     

Ceratosphinctes (Ammonitina, Kimmeridgian) in Mexico: from rare but typical inhabitant of west-Tethyan epioceanic and epicontinental waters to a geographically widespread ammonite genus

Two specimens of Ceratosphinctes represent the first record of this taxon in Mexico (Mexican Huasteca), and are interpreted as Ceratosphinctes rachistrophus amatitlaensis nov. subsp. The subspecies level is used with biogeographic significance, most probably indicating incoming propagules and adaptation to local environmental requirements. Biostratigraphy, based on agreement of the composition of the ammonite assemblage that included C. rachistrophus amatitlaensis nov. subsp. and the previous interpretation of ammonite assemblages with Idoceras in Mexico by Villaseñor et al., indicates precise correlation with Tethyan records (uppermost-Lower to lowermost-Upper Kimmeridgian). The dispersion pattern available for Ceratosphinctes is interpreted as related to ecospace enlargement during the relative sea-level highstand of the late-Early Kimmeridgian.