Reproductive success of arbore weed Sambucus nigra in the Abies religiosa temperate forest of the Magdalena river basin, Mexico City
The study of reproductive success of weed species is crucial for understanding their colonization dynamics. Sambucus nigra, a weed distributed in disturbed areas and in sites of open canopy in the Abies religiosa temperate forest of the Magdalena river basin, which is part of the vegetation and soil remnants under conservation in Mexico City. The aim of this study is to know the biotic and abiotic factors related to the reproductive phenology and germination requirements of S.nigra. The percentages of flowers, young and mature fruits of 103 individuals of S. nigra were recorded for one year (2012), as well as factors such as precipitation, temperature, light and some soil chemical properties. Seeds were collected in August 2014 and were buried in the soil for three months (October, November and December 2014). Two treatments were then applied: a set of seeds was scarified with sulfuric acid (90 %), and the other one was cold stratified (3 °C). All seeds were then germinated under fluctuating temperatures (12/20 ° C) and under four different light treatments (red, far red, white light and dark) in germination chambers.
The results showed that the percentages of flowers increased during the season with higher solar irradiation and less soil moisture, while the fruit-percentages increased when higher precipitation and temperatures were registered. The Canonical Correspondence Analysis of the reproductive phenology and environmental factors showed three micro-environmental groups. Germination percentages were of 25% under fluctuating temperatures (12/20 ° C), and responded equally to the different light treatments. There was no germination for scarified seeds. A higher germination percentage was registered for seeds under cold stratification (5% higher). S. nigra showed plasticity and variable responses to the environmental factors and to the spatial heterogeneity in the study site as well as variable germination under a wide range of conditions.