UNIVERSITÄTSBIBLIOTHEK BRAUNSCHWEIG Dietmar Brandes & Maren Belde Population dynamics and ecology of Xanthium albinum Botanikertagung Braunschweig 24: Neophyten und Biodiversität URL: http://www.digibib.tu-bs.de/?docid=16335
Botanikertagung Braunschweig 24: Neophyten und Biodiversität Population dynamics and ecology of Xanthium albinum Dietmar Brandes (TU Braunschweig) & Maren Belde (TU München)
Xanthium albinum (Asteraceae( Asteraceae) The genus Xanthium (cocklebur) comprises several related species in the temperate world. Their taxonomy is still confusing. Xanthium albinum differentiated from Xanthium saccharatum after its introduction to Europe. Xanthium albinum is a shortlived annual growing at riverbanks especially in the river system of the Elbe. It was first found at the banks of the river Netze (Poland) in 183.
Zonation of the vegetation Phalaris arundinacea Carex acuta Xanthium albinum Groyne field of the middle course of the river Elbe at Lenzen.
Germination of Xanthium albinum: the seedlings emerge immediately if the water level goes down.
Germination Xanthium albinum is a warmth-germinator Usually only one achene per bur germinates 7 Germinated Achenes [%] 6 5 4 3 2 1 NL, 25 C TL, 25 C Achänen (g), 25 C NL, 1/25 C TL, 1/25 C Achänen (g),1/25 C 5 1 15 2 25 3 Time after Sowing [d] NL: storage under water; TL: dry storage; g: both achenes separated.
Germination Germinated achenes [%] 5 45 4 35 3 25 2 15 1 5 21 21 217 231 277 15 C 2 C 25/26 C 3/32 C Storage time of the burs under water [d] Most burs have to hibernate under water. Germination depends on storage time of the burs under water.
Growth and development The aboveground biomass correlates with the mean growth height (R = +,99) in stands dominated by Xanthium albinum. The aboveground biomass could be remarkably high (maximum: 885 g/m²). Xanthium albinum is a short-day plant. The flowering induction occurs at a dark period of 7.5 h, however influenced by temperature and age of the plants. Xanthium albinum is self-fertil.
1% Biomass distribution during a vegetation period 8% 6% 4% Fruchtstände (>=15mm) Fruits (> 15 mm) Female Flowers / Fruits (< 15 mm) Male Flowers w eibl. Blüten-/ Fruchtstände (<15mm) männl. Blütenstände Leaves Laubblätter Keimblätter Cotyledons Lateral Branches Seitensproßachsen 2% Stem Axis Hauptsproßachsen % 2.6. 2.6. 26.6. 19.7. 27.7. 4.8. 7.8. 18.8. 26.9.
Mortality Mortality is of fundamental importance for the population dynamics as well as for the germination. The infraspecific competition is of low importance with respect to the mortality of the seedlings of Xanthium albinum. Larger embryos have larger resources and therefore possibly adventage in competition, because the length of the cotyledons reflects the size of the achenes. No difference was detected between the length of the cotyledons of surviving and dead plants.
Mortality 8 (A) Sum of germinated achenes Idividuals' number 7 6 5 4 3. (B) Sum of dead plants (C) Number of surviving individuals 2 1 6.5. 26.5. 15.6. 5.7. 25.7. 14.8. 3.9. 23.9. Date Dynamics of a population: sum of germinated achenes (A), sum of dead plants (B), and the number of living indivuals (C). Permanent plot 1: 72 germinated induviduals, area 42 m²
Mortality 35 6 Daily Mean Temperature [ C] Sum of Precipitation [cm] 3 25 2 15 1 5 5 4 3 2 1 Death rate [%] 16.4. 6.5. 26.5. 15.6. 5.7. 25.7. 14.8. 3.9. 23.9. 13.1. Date Correlation between death rate and weather variation (same plot).
Intraspecific competition Density-yield yield relationships and reproductive allocation 25 Mean fruits per plant 2 15 1 5 5 1 15 2 25 Density of Xanthium albinum [1/m²] Increasing plant density reduces the number of burs per plant.
Intraspecific competition Density-yield yield relationships and reproductive allocation 18 16 Sum of fruits [1/m²] 14 12 1 8 6 4 6 44 48 54 2 5 1 15 2 25 Density of Xanthium albinum [1/m²] If the density exceeds 43 plants/m², the production of burs per m² also decreases rapidly.
Interspecific competition: Influence of Phalaris arundinacea on the production of diaspores S um of fruits [1/m ²] 3 25 2 15 1 5 1 2 3 4 5 Density of Xanthium albinum [1/m²] Phalaris arundinacea is the most frequent companion. 8 plots having a cover of Phalaris arundinacea of at least 6 %. Strong linear correlation between low densities of Xanthium albinum and sum of burs; R = +,99.
Interactions with Herbivores Slugs Mice Cattle (Cow, Sheep, Horse) The seedlings are toxic for animals (Cole et al. 198) Grazing by sheep near Brambach: Xanthium albinum is only affected moderately.
Interactions with parasites Xanthium albinum parasitised by Cuscuta campestris.
Interactions with Cuscuta campestris ha Cross section of the stem of Xanthium albinum with haustoria (ha) of Cuscuta campestris.
Parasitism by Cuscuta campestris 35 3 CC 1 BM 8 Biomass [g DS/m²] 25 2 15 1 5 63% reduction Cuscuta campestris Haupt- Stem sproß- achsen Axis Seitensproßachsen Lateral Male Branches Parts of Xanthium albinum Fruits <15mm Fruits Laubblätter männl. w eibl. Bl.-/ Leaves Female Fruits Blütenstände Flowers/ (<15mm) Fr.-stände Organe Xanthium von albinum Fruchtstände (>=15mm) >15mm Comparison of the two plots CC1 and BM8: CC1: 1 m², cover of Xanthium albinum 7 %, total biomass 578 g/m² BM8: 1 m², cover of Xanthium albinum 8 %, total biomass 739 g/m²
Conclusions Xanthium albinum is able to realize a very special niche, which is partly not realized by indigenous species. It invades short-lived nitrophilous riverside communities (Chenopodion fluviatile) and also some communities of Bidention. Xanthium albinum needs large rivers with pluvial regime (low water in summer and autumn) and sandy river banks. The consolidation of the inland waterway system with groynes obviously facilitates its establishing. Xanthium albinum passes very rarely the dikes. Xanthium albinum shows no trend to become weedy till now.
Displacement of native species? There is no influence of the cover of Xanthium albinum on the phytodiversity (number of companion species) of the 7 plots of 1m². (Median and mean). Number of Species 2 18 16 R 2 =,3685 14 12 1 8 R 2 =,1 6 4 Median 2 Mean 2 4 6 8 1 Cover of Xanthium albinum (%) We also found no correlation between vitality of Xanthium albinum (burs/m²) and phytodiversity! Number of other species 4 35 3 25 2 15 1 5 y = -,2x + 11,699 R 2 =,2 5 1 15 2 Number of burs >= 15 mm
Neophytes vs. phytodiversity of riverbanks We found a positive correlation between the number of neophytes (post-1492 aliens) and the number of all species for 7 rivers fully investigated in Germany. Our hypothesis: Species-rich habitats are in a higher degree invaded by alien species than species-poor habitats. (There are no differences between neophytes and indigenous species in principle). Our results support the idea of Klotz (2). Number of neophytes 12 1 8 6 4 2 R 2 =,7957 2 4 6 Sum of species Rivers: Oker, Schunter, Wabe, Ilse, Weser, Rur*, Saar**. *Kasperek 1996,**Ludewig 1999.