Seed bank analysis and its relation to the standing vegetation in an abandoned field of the pampean prairie

La regeneración de la comunidad vegetal, luego de sufrir algún tipo de disturbio, depende de la disponibilidad de propágulos cuya fuente primaria la constituye el banco de semillas del suelo. El objetivo de este trabajo fue analizar la composición florística, abundancia, riqueza y diversidad del banco de semillas y de la comunidad vegetal, y evaluar la relación entre ambos, en un lote agrícola de la llanura pampeana donde se desarrolló una sucesión secundaria a lo largo de 20 años. En la vegetación se registraron 13 especies, entre las cuales predominaron especies perennes y Sorghum halepense fue la dominante. En el banco de semillas se identificaron 12 especies, con predominio de especies anuales. Tres especies: Sorghum halepense, Carduus acanthoides y Verbena bonariensis estuvieron presentes en el banco de semillas y en la vegetación, pero sólo S. halepense mostró una correlación significativa y positiva. Esta escasa relación entre la vegetación y el banco de semillas sugiere que el banco de semillas puede ser de limitada importancia en el reclutamiento, estructura y composición de la comunidad vegetal.The regeneration of plant community after disturbance depends on the availability of propagules. In grasslands, soil bank is the primary source of propagules, although propagule arrival from neighbouring areas may be important as well. There is evidence that in several grasslands there is a low similarity in floristic composition and in the relative abundance of plant species between the standing vegetation and their soil seed banks. The objective of this study was to evaluate the floristic composition, abundance, richness and diversity of the soil seed bank and the standing vegetation and to assess their relationship, in a closed field of the pampean prairie where a secondary succession has developed after 20 years. Thirty-six samples of vegetation and soil were analysed, classified and ordered with multivariate methods. In the standing vegetation, we recorded a total of 13 species, most of them perennials. The dominant species was Sorghum halepense. In the seed bank, we identified 12 species, most of them annuals, and Portulaca oleracea was the most abundant one. The floristic groups of the standing vegetation were more clearly defined than those groups of the soil seed bank. Three species (Sorghum halepense, Carduus acanthoides and Verbena bonariensis) were present in both the seed bank and the standing vegetation, but only for S. halepense showed a positive correlation between both the seed bank and the standing vegetation. The low similarity between the standing vegetation and the soil seed bank shows that, except for Sorghum halepense, the dominant species of the standing vegetation contribute very little to the development of the soil seed bank

The seed bank of an old pampean prairie and its relation with the standing vegetation

Analisou-se o banco de sementes de uma pastagem que não foi arada pelo menos durante 40 anos. Comparou-se com a vegetação do lugar. Acharam-se 28 espécies no banco de sementes: 18 monocotiledôneas e 10 dicotiledôneas, mais cinco espécies desconhecidas. Na vegetação foram arroladas 39 espécies: 19 monocotiledôneas e 20 dicotiledôneas. O banco de sementes comparte 18 espécies, das 49 conhecidas, com a vegetação, e a similitude entre elas é de 54% (índice de Sorensen). As sementes têm distribuição agregada, constituindo um banco muito heterogêneo.The seed bank of a prairie which has not been ploughed for at least 40 years was analysed and compared with standing vegetation. There were 28 species in the seed bank: 18 monocotyledoneae and 10 dicotyledoneae, plus five unknown species. In the standing vegetation there were 39 species: 19 monocotyledoneae and 20 dicotyledoneae. Seed bank and standing vegetation share 18 out of 49 known species and their similarity is 54% (Sorensen index). The seeds have an aggregate distribution, therefore the bank is very heterogeneous