Nitrogen (N) pollution is a global threat to the biodiversity of many plant communities, but its impacts on grassland soil seed banks are unknown. Here we show that size and richness of an acid grassland seed bank is strongly reduced after 13 years of simulated N deposition. Soils receiving 140 kg N ha À 1 per year show a decline in total seed abundance, seed species richness, and the abundance of forbs, sedges and grasses. These results reveal larger effects of N pollution on seed banks than on aboveground vegetation as cover and flowering is not significantly altered for most species. Further, the seed bank shows no recovery 4 years after the cessation of N deposition. These results provide insights into the severe negative effects of N pollution on plant communities that threaten the stability of populations, community persistence and the potential for ecosystems to recover following anthropogenic disturbance or climate change.

Aim Climate and land use are key determinants of biodiversity, with past and ongoing changes posing serious threats to global ecosystems. Unlike most other organism groups, plant species can possess dormant life‐history stages such as soil seed banks, which may help plant communities to resist or at least postpone the detrimental impact of global changes. This study investigates the potential for soil seed banks to achieve this. Location Europe. Time period 1978–2014. Major taxa studied Flowering plants. Methods Using a space‐for‐time/warming approach, we study plant species richness and composition in the herb layer and the soil seed bank in 2,796 community plots from 54 datasets in managed grasslands, forests and intermediate, successional habitats across a climate gradient. Results Soil seed banks held more species than the herb layer, being compositionally similar across habitats. Species richness was lower in forests and successional habitats compared to grasslands, with annual temperature range more important than mean annual temperature for determining richness. Climate and land‐use effects were generally less pronounced when plant community richness included seed bank species richness, while there was no clear effect of land use and climate on compositional similarity between the seed bank and the herb layer. Main conclusions High seed bank diversity and compositional similarity between the herb layer and seed bank plant communities may provide a potentially important functional buffer against the impact of ongoing environmental changes on plant communities. This capacity could, however, be threatened by climate warming. Dormant life‐history stages can therefore be important sources of diversity in changing environments, potentially underpinning already observed time‐lags in plant community responses to global change. However, as soil seed banks themselves appear, albeit less, vulnerable to the same changes, their potential to buffer change can only be temporary, and major community shifts may still be expected.

Climate change models project shifts in precipitation patterns at regional and global scales. Increases in dry areas and the occurrence of drought predicted in future scenarios are likely to threaten grassland ecosystems. Calcareous grassland seed banks have proven to be resistant to short-term drought, but their responses to long-term drought are unknown. Here we show that 14 years of summer drought changed calcareous grassland seed bank composition, reducing its size and richness, and that these responses do not simply reflect patterns in the above-ground vegetation. Moreover, the effect of drought was larger on seed banks than on vegetation, and above-ground responses mediated by soil depth were less evident in the seed bank than in the vegetation. These results demonstrate that the severity of drought effects on calcareous grasslands is larger than previously thought, and show that this ecosystem is highly vulnerable and has low resilience to predicted decreases in soil moisture.

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Abstract. To evaluate the organogenic potential of Cedrela montana Moritz ex Turcz, explants from mature (10-20 year-old) and juvenile (7-18 month-old) trees were collected. The first grouping included buds, leaves, and nodes derived from juvenile basal offshoots and rejuvenated shoots from cuttings. The second, included leaves, petioles, nodes, internodes and nodes of in vitro elongated shoots. The highest organogenic potential was observed in nodes from juvenile trees: 45.8% of explants presented axillary bud elongation, while 56.2% presented rooting in a growth regulator free culture medium. Fiftyone percent of elongated shoots produced adventitious shoots with 0.5 µM NAA and 0.5 µM BA; 30% with 0.5 µM NAA and 1 µM BA; and 30% with 1 µM BA. Twenty percent presented roots with 0.5 µM NAA. Root formation was stimulated in a medium supplemented with activated charcoal (5 gL -1 ). The acclimatization of eighty percent of plantlets regenerated from nodes, and of 72.5% in vitro generated shoots was successful. On the contrary, mature trees material presented low organogenic response. Axillary bud elongation was recorded just in 10.7% of explants from juvenile shoots and in 6.7% of explants from rejuvenated shoots. In conclusion the age of donor plant and type of explant affect the organogenic potential of C. montana. This study contributes to the understanding of this species' response under in vitro conditions. Key words: Cedrela montana, Meliaceae, tropical forestry, woody plant tissue culture, in vitro, vegetative propagation.Efecto de la edad del material parental y del tipo de explante en el cultivo in vitro de Cedrela montana Moritz ex Turcz. Resumen. Para evaluar el potencial organogénico de Cedrela montana Moritz ex Turcz, se colectaron explantes de árboles maduros (10-20 años) y juveniles (7-18 meses). Los primeros incluyeron yemas, hojas y nudos de brotes juveniles (ubicados hacia la parte basal del tronco) y rejuvenecidos (obtenidos a partir de estacas). Los segundos hojas, peciolos, nudos, entrenudos y nudos de brotes elongados in vitro. Los nudos de árboles juveniles presentaron el mayor potencial organogénico, ya que el 45,8% de los explantes presentaron elongación de yemas axilares y el 56,2% enraizamiento en medio sin reguladores de crecimiento. El 51% de los brotes elongados formaron brotes adventicios con 0.5 µM NAA y 0.5 µM BA, el 30% con 0.5 µM NAA y 1 µM BA, y el 30% con 1 µM BA; y el 20% raíces con 0,5 µM NAA. La formación de raíces se vio estimulada con la adición de carbón activado (5 gL -1 ) en el medio. El 80% de las plántulas regeneradas a partir de nudos y el 72,5% de las provenientes de brotes generados in vitro se aclimataron exitosamente. Por el contrario, explantes de árboles maduros presentaron baja respuesta organogénica. Elongación de yemas axilares fue registrada solamente en 10.7% de los nudos de brotes juveniles y en 6.7% de aquellos provenientes de brotes rejuvenecidos. En conclusión, la edad de la planta donadora y el tipo de explante influyen sobre el potencial organogénico ...