We assessed inter-seasonal dynamics of seed banks, dormancy and seed germination in three endemic Chihuahuan Desert succulent species, under simulated soil warming conditions. Hexagonal open top-chambers (OTCs) were used to increase soil temperature. Seeds of Echinocactus platyacanthus (Cactaceae), Yucca filifera and Agave striata (Asparagaceae) were collected and buried within and outside OTCs. During the course of one year, at the end of each season, seed batches were exhumed to test viability and germination. Soil temperature in OTCs was higher than in control plots. Yucca filifera seeds always had high germination independently of warming treatment and season. Agave striata seeds from OTCs had higher germination than those from control plots. Agave striata exhibited low germination in fresh seeds, but high germination in spring. Seeds from this species lost viability throughout the experimental timeframe, and had no viable seeds remaining in the soil. Echinocactus platyacanthus showed high germination in fresh seeds and displayed dormancy cycling, leading to high germination in spring, low germination in summer and autumn, and high germination in winter. Germination of this species was also higher in seeds from OTCs than those from control plots. Echinocactus platyacanthus formed soil seed banks and its cycle of inter-seasonal dormancy/germination could be an efficient physiological mechanism in a climate change scenario. Under global warming projections, our results suggest that future temperatures may still fall within the three studied species’ thermal germination range. However, higher germination for A. striata and E. platyacanthus at warmer temperatures may reduce the number of seeds retained in the seed bank, and this could be interpreted as limiting their ability to spread risk over time. This is the first experimental study projecting an increase in soil temperature to assess population traits of succulent plants under a climate change scenario for American deserts.
Most wild Lupinus spp. (Fabaceae) grow in pine and pine-oak forests with natural and induced fi res. Their seeds have physical dormancy, which can be broken in response to appropriate environmental signals, such as high temperatures, humidity, and fi re. We applied heat treatments to break seed dormancy of L. elegans and L. rotundifl orus from the State of Jalisco, Mexico, with different storage times (0, 1, and 2 yr for L. elegans and 0, 1, 2, 3, and 4 yr for L. rotundifl orus). One set of seeds were immersed in boiling water for 5, 10, and 15 s, another set were incubated in wet or dry sand at 100 °C, 120 °C, and 150 °C during 60 min and 90 min. Germination trials were set at 25 °C with 12 h of irradiance per day. For both species, no germination resulted after incubation at 120 and 150 °C. For L. rotundifl orus, germination was higher for seeds incubated in wet sand for 60 min than for those incubated for 90 min. Fresh seeds of L. rotundifl orus showed higher germination than stored seeds across treatments. After scarifi cation with boiling water, fresh seeds of L. elegans, germinated more than those stored for 1 and 2 year, whereas incubation in wet and dry sand resulted in higher germination for 1 and 2 year old seeds than for fresh seeds. Our results may be useful for further studies to understand and predict ecological plant responses in Mexican forests. Key words: boiling water, dry sand, seed germination, wet sand.Resumen: La mayoría de las especies silvestres de Lupinus (Fabaceae) crecen en bosques de pino y pino-encino, en donde se presentan incendios naturales e inducidos. Sus semillas tienen latencia física, la cual puede ser rota en respuesta a señales ambientales como altas temperaturas, humedad y fuego. En esta investigación, se aplicaron tratamientos de calor para romper la latencia de semillas de L. elegans y L. rotundifl orus del estado de Jalisco, México, con diferentes tiempos de almacenamiento (0, 1 y 2 años para L. elegans y 0, 1, 2, 3 y 4 años para L. rotundifl orus). Un grupo de semillas fue sumergido en agua hirviendo por 5, 10 y 15 segundos, otro grupo fue incubado en arena húmeda o seca a 100, 120 y 150 °C durante 60 y 90 minutos. Las semillas se pusieron a germinar a 25 °C con fotoperíodo de 12 horas. Para ambas especies, no hubo germinación en semillas incubadas a 120 y 150 °C. Para L. rotundifl orus, la germinación fue más alta en semillas incubadas en arena húmeda por 60 minutos que por 90 minutos. Las semillas frescas de L. rotundifl orus mostraron mayor germinación que las almacenadas, en los distintos tratamientos. Después de la escarifi cación con agua hirviendo, las semillas frescas de L. elegans germinaron más que las almacenadas por 1 y 2 años, mientras que para las semillas almacenadas por 1 y 2 años la incubación en arena húmeda y seca resultó en mayor germinación que para las semillas frescas. Estos resultados podrían ser útiles para entender y predecir respuestas ecológicas de las plantas en bosques mexicanos. Palabras clave: agua hirviendo, arena húmeda, aren...
Enterolobium cyclocarpum and Piscidia piscipula are two important tree Fabaceae species distributed from the Yucatan Peninsula, Mexico. Our aims were focused on the E. cyclocarpum and P. piscipula seeds for: (1) to examine the seed permeability and imbibition rate, (2) to evaluate the effect of seed pre-germinative treatments, and (3) to characterize the structures involved on the presence of physical dormancy (PY). We used fresh seeds to determine seed permeability and imbibition rate, seed viability by means of tetrazolium test, furthermore, we applied mechanical scarification and boiler shocks for 5 s, 10 s and 15 s treatments. Morphological characterization of the seed coat was by Scanning Electron Microscope (SEM). Seed viability in E. cyclocarpum and P. piscipula were 100% and 96%, respectively. Seed permeability and imbibition rate in E. cyclocarpum were low. The highest germination in E. cyclocarpum was in the mechanical scarification (92%), while in P. piscipula, this parameter was in the 10 s boiling water treatment (76.0%). The presence of PY was confirmed in both species because they showed low seed permeability, and imbibition rate; furthermore, exhibited macrosclereids cells. The present research seeks to promote the sustainable use of E. cyclocarpum and P. piscipula.
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