Seed ecology: a diverse and vibrant field of study

My purpose is to introduce a special issue of Seed Science Research devoted to papers resulting from material presented at Seed Ecology V held in Caeté, Brazil on 21–25 August 2016. An overview of the field of seed ecology is presented that includes a short summary of what I consider to be the eight basic subcategories of this field, and the five new areas of investigation that have developed as extensions and/or recombinations of basic areas. Seed ecology conferences allow researchers to communicate with each other and build new collaborative relationships. At Seed Ecology V, information was presented that related to each area of seed ecology. The nine papers in this special issue are a small sample of the information presented at the meeting, and each paper is briefly described and placed into one of the subcategories of seed ecology research.

Seed ecology informs restoration approaches for threatened species in water-limited environments: a case study on the short-range Banded Ironstone endemic Ricinocarpos brevis (Euphorbiaceae)

Translocation of threatened species is challenging in semiarid environments, especially when seeds are the principal means of in situ establishment. Worldwide, the overall success of translocations using seeds is highly variable and generally unpredictable. Most seed-based translocations are embarked upon with limited understanding of the species’ seed biology or the nuances of the local abiotic environment in which to guide restoration approaches. For instance, within Australia just 14% of threatened species translocations use directly sown seeds and consequently, to improve the chances of restoration success, both the seed biology and the influence of the abiotic environment need to be adequately understood. We investigated these aspects in Ricinocarpos brevis R.J.F.Hend. & Mollemans – a short-range Banded Ironstone endemic – by focusing on a series of laboratory and field experiments to understand the key drivers of dormancy alleviation and germination promotion, as well as in-situ conditions of natural and recipient translocation sites. Fresh seeds were found to have high viability, fully developed linear embryos and possess physiological dormancy, with enhanced germination when exposed to smoke water, karrikinolide (KAR1) and gibberellic acid (GA3). Under laboratory conditions, seeds germinated over a range of temperatures (15−30°C), but germination was suppressed by light and highly sensitive to water stress. Seeds had reduced germination when sown on the soil surface, but could emerge from up to 13 cm in depth. Under field conditions, in-situ emergence was <2%. Using in-situ emergence results, soil loggers and rainfall data, we developed a model of the recruitment bottlenecks faced by this species under in-situ conditions, an approach that provides useful insights to assist future translocations. Understanding seed biology and seed ecology enables better insights into the principal bottlenecks restricting in-situ emergence and consequently restoration success, leading to the development of more effective approaches for conserving other threatened flora in future.

Seed ecology of Captain Cook tree [Cascabela thevetia (L.) Lippold] – germination and longevity

Cascabela thevetia (L.) Lippold (Apocynaceae), commonly known as Captain Cook tree or yellow oleander, has established large infestations in riparian areas along several creeks and rivers in northern Queensland. To better understand the ecology of C. thevetia and the implications for its spread and management, this study reports seven experiments related to the seed ecology of its yellow and peach biotypes. We quantified its germination response to ambient (Experiment 1a and 1b), alternating and constant temperature (Experiment 2a and 2b) regimes and exposure to different light conditions (Experiment 3). Seed longevity under two soil types, two levels of pasture cover and three burial depths was also determined (Experiment 4a and 4b). Both loose seeds and seeds still within pods (kernels) of the two biotypes of C. thevetia were able to germinate in all months of the year in northern Queensland, irrespective of the large differences in monthly ambient temperatures experienced at the Charters Towers study site. Both biotypes also germinated across a wide range of alternating day/night temperatures from 16/12°C to 47/37°C and constant temperatures from 17°C to 44.0°C. Germination of the two biotypes was significantly greater (4-fold) and faster (7 days earlier) under shade than under natural light conditions. Over all biotypes, soil types, levels of pasture cover and burial depths, no seeds of C. thevetia remained viable after 2 years: longevity was much less in many circumstances. The results demonstrate that C. thevetia seeds can germinate over a wide temperature range, whereas the ability of seed to remain viable at low temperatures highlights the potential for expansion of its current potential distribution towards southern latitudes of the Australian continent. Across all experimental conditions, the yellow biotype displayed superior seed germination and viability traits compared with the peach biotype. Seed banks of the peach and yellow biotypes of C. thevetia are short-lived (2 years), which may be exploited when developing management strategies to reduce its impacts.