Untersuchungen zur Dynamik von generativen Diasporenbanken von Samenpflanzen in Kalkmagerrasen.: I. Jahreszeitliche Dynamik des Diasporenregens und der Diasporenbank auf zwei Kalkmagerrasenstandorten der Schwäbischen Alb.

Abstract

Summary The seasonal dynamics of diaspore rain (seed rain) and diaspore bank in the soil (seed bank) in two different calcareous grassland sites on the Suebian Alb (South Germany) was investigated. The first site, the “Dachswiesle”, is mowed once a year in August, the vegetation is a Mesobrometum. The second site, “Leimberg”, was grazed until quite recently. The vegetation is a Gentiano-Koelerietum. The composition of diaspore rain and diaspore bank represents almost exclusively the actual vegetation on these sites. The number of diaspores present in the soil at both sites in spring was 6000 to 7000/m2 The seasonal dynamics of diaspore rain and bank in the soil and the distribution of the diaspores in upper and lower soil layers allowed the classification of species in the following groups (Fig. 3, Tab. 5): Type 1a: Species with dispersal during the vegetation period; diaspores without innate dormancy and only in the upper soil layer during the vegetation period; persistence: transient ( Type 1b: Species with dispersal during vegetation period, diaspores with innate dormancy (broken line; drawn line; e.g.: Polygala amarella, P. comosa a.o.); species with dissemination at the end of the vegetation period or in winter, diaspores without or with innate dormancy (dotted line; e.g.: Carlina vulgaris, Cirsium acaule, Fig. 6; Pimpinella saxifraga, Fig. 7); only in the upper soil layer from the beginning of dispersal until spring; persistence: transient ( Type 2a: Species with dispersal during the vegetation period, diaspores without innate dormancy and with few exceptions only in the upper soil layer during the whole year with a maximum in the vegetation period, persistence: transient (1 to 2 years); e.g.: Scabiosa columbaria (Fig. 9). Type 2b: Species with dispersal during the vegetation period, diaspores with innate dormancy (broken line; drawn line; e.g.: Euphrasia rostkoviana); species with dispersal at the end of the vegetation period or in winter, diaspores with or without innate dormancy (dotted line; e.g.: Asperula cynanchica; Fig. 11); with few exceptions only in the upper soil layer during the whole year with a maximum from the beginning of dissemination until spring; persistence: transient (1 to 2 years). Type 3a: Like 2a, but dormancy of diaspores can be enforced by unfavourable environmental factors; high numbers of diaspores in the upper bottom layers compared to the number in lower soil layers; maximum in the upper soil layers during vegetation period; persistence: persistent (some years to some decades); e.g.: Lotus corniculatus(Fig. 12), Ranunculus bulbosus. Type 3b: Like 2b, but dormancy of diaspores can be enforced by unfavourable environmental factors; high numbers of diaspores in the upper soil layers compared to the number in lower soil layers; maximum in the upper bottom layers from the beginning of dispersal until spring; persistence: persistent (some years to some decades); e.g.: Hippocrepis comosa, Plantago media(Fig. 13). Type 4: Species with dissemination during vegetation period or until spring, diaspores with or without innate dormancy, dormancy can be enforced or induced by unfavourable environmental factors; high numbers of diaspores in the lower soil layers with no or hardly any recognizable maximum in the upper soil layer; persistence: persistent (some decades); e.g.: Carex flacca (Fig. 14, 15), Linum catharticum (Fig. 16), Potentilla neumanniana (Fig. 17). The comparison of Populations of the same species on both sites show no great differences in the persistence of the diaspore bank. There are only differences in the timing of the maximum of diaspores in the upper bottom layer during the year, depending on the seasonal dynamics of diaspore rain (Fig. 4, 5, 8, 9, Tab. 4,5).