Effects of hydropriming and natural priming on seed germination of two perennial herbs in a disturbed lava field in central Mexico

Background/Question/Methods

Priming has proved to enhance seed germination by increasing germination rates and percentages. It also increases seedling emergence and establishment. Hydropriming improves germination by the hydration and subsequent dehydration of seeds, triggering metabolic changes before germination occurs. When buried, seeds can undergo a natural priming process due to fluctuations in environmental cues. When seeds are re-hydrated, a major part of the germination metabolic process has already started and higher germination rates, which confer ecological advantages for colonization, are attained. We analyze the germination response after natural priming and hydropriming of two common perennial herbs growing on a disturbed lava field, at Mexico City’s Ecological Park. Castilleja tenuiflora is a hemiparasitic Orobanchaceae that flowers throughout the year, although fruit production shows a clear seasonal peak. Penstemon roseus, a Plantaginaceae, reproduces in late autumn. Seed moisture content and photoblastism were determined by standard methods. Seeds were soaked during 24 hours, allowed to dry during one week, and then placed in germination chambers in order to determine responses to hydropriming. To identify the effects of natural priming on germination, seeds were placed in natural conditions and then recovered every two months and placed in germination chambers. Germination percentages and rates were then quantified.

Results/Conclusions

The seed moisture content of these species increased after soaking, proving that the seed coat is permeable to water, and allowing them to seize the random precipitation that falls before the rainy season is fully established. This induces the natural priming of seeds. Penstemon roseus seeds are orthodox and positive photoblastic, as could be expected due to the small size of the seeds. Natural priming and hydropriming increased germination rates. However, final germination percentage decreased after the rainy season in recovered seeds, and no further germination was observed, suggesting that P. roseus forms a short-term, transient seed bank that lasts from seed dispersal in autumn through the rainy season in summer. Castileja tenuiflora also has orthodox seeds, but they are indifferent to light quality, despite being also very small. This response is probably related to the hemiparasitic character of this species, for underground germination can enhance the contact with potential host roots. Both priming treatments improved the germination response of this species. Germination strategies that characterize these two species allow them to occupy suitable microsites for germination and establishment. These responses can be helpful in developing restoration programs based on the accelerated establishment of native and characteristic sucesional species.