Jerry M. Baskin

Germination Ecology of Seeds in the Persistent Seed Bank

This chapter illustrates aerial and buried persistent seed banks, longevity of seeds in the soil, the fate of seeds while they are in the soil, and effects of seed banks on populations of species and persistence of communities. A transient seed bank consists of seeds that do not live until the second germination season following maturation. Seeds of some species remain in a transient seed bank for several months, during which the dormancy loss occurs. However, the environmental conditions in these habitats are unfavorable for germination. Seeds of other species may be nondormant at maturity. However, a persistent seed bank consists of seeds that live until the second germination season. In general, seeds with a high probability of forming persistent seed banks are small and have smooth seed coats. But those with a low probability of forming persistent seed banks are relatively large and have hooks, awns, spines, or other kinds of projections on the seed coat. Therefore, biologists are more interested in persistent than in transient seed banks

Seed dormancy and persistent sediment seed banks of ephemeral freshwater rock pools in the Australian monsoon tropics

BACKGROUND AND AIMSnRock pools are small, geologically stable freshwater ecosystems that are both hydrologically and biologically isolated. They harbour high levels of plant endemism and experience environmental unpredictability driven by the presence of water over variable temporal scales. This study examined the hypothesis that the sediment seed bank in monsoon tropical freshwater rock pools would persist through one or more periods of desiccation, with seed dormancy regulating germination timing in response to rock pool inundation and drying events.nnnMETHODSnSeeds were collected from seven dominant rock pool species, and germination biology and seed dormancy were assessed under laboratory conditions in response to light, temperature and germination stimulators (gibberellic acid, karrikinolide and ethylene). Field surveys of seedling emergence from freshwater rock pools in the Kimberley region of Western Australia were undertaken, and sediment samples were collected from 41 vegetated rock pools. Seedling emergence and seed bank persistence in response to multiple wetting and drying cycles were determined.nnnKEY RESULTSnThe sediment seed bank of individual rock pools was large (13u2009824u2009±u2009307 to 218u2009320u2009±u200942u2009412xa0seedsxa0m(-2) for the five species investigated) and spatially variable. Seedling density for these same species in the field ranged from 13u2009696 to 87u2009232 seedlings m(-2). Seeds of rock pool taxa were physiologically dormant, with germination promoted by after-ripening and exposure to ethylene or karrikinolide. Patterns of seedling emergence varied between species and were finely tuned to seasonal temperature and moisture conditions, with the proportions of emergent seedlings differing between species through multiple inundation events. A viable seed bank persisted after ten consecutive laboratory inundation events, and seeds retained viability in dry sediments for at least 3 years.nnnCONCLUSIONSnThe persistent seed bank in freshwater rock pools is likely to provide resilience to plant communities against environmental stochasticity. Since rock pool communities are often comprised of highly specialized endemic and range-restricted species, sediment seed banks may represent significant drivers of species persistence and diversification in these ecosystems.

Germination Ecology of Seeds with Physical Dormancy

This chapter discusses germination phenologies of seeds with physical dormancy. It also illustrates the role of drying in the development and maintenance of physical dormancy. Most of the information on the germination requirements of seeds (after physical dormancy is broken) comes from studies in which various laboratory techniques have been used to make seeds permeable. The examples of germination phenology of seeds with physical dormancy are the species growing in a temperate climate with hot, moist summers, and cold, wet winters. Seeds of many species with physical dormancy grow in subtropical or tropical regions with annual wet and dry seasons, and germinate at the beginning of the wet season. Thus, a survey is performed on the methods for artificially breaking physical dormancy, as well as germination requirements for seeds after they become permeable. The role of various environmental factors in the breaking of physical dormancy is also examined. Finally, attention is given to how physiological dormancy is broken in those seeds with both physical and physiological dormancy.

A Geographical Perspective on Germination Ecology: Tropical and Subtropical Zones

This chapter illustrates what is known about the germination ecology of plants growing in various types of vegetation throughout the world. To facilitate organization of the mass of literature, classification system of the vegetation zones has been adopted as a general outline. Vegetation is divided into two broad categories, such as tropical and subtropical zones, and next, temperate and arctic zones. This chapter discusses the germination ecology of plants in tropical and subtropical zones, whereas chapter 10 deals with the species in temperate and arctic zones. The germination ecology of plants in each of these four vegetation zones, as well as that of species on tropical mountains is covered. For each type of vegetation, a detailed discussion along with a summary on the germination of trees, shrubs, vines, and herbaceous species is made available. Weeds are also considered, and attention is given to special biotic and abiotic factors influencing germination. Although environmental conditions associated with shade on the forest floor are required for the germination of some seeds, these conditions may be favorable for the growth of seedlings and juveniles. Many canopy, as well as emergent, tree species require a gap in the canopy, and thus, an increase in light, before young individuals can grow to maturity.

Variation in Seed Dormancy and Germination within and between Individuals and Populations of a Species

This chapter covers (1) the inheritance of seed dormancy and dormancy-breaking and germination requirements; (2) effects of inbreeding on seed germination; (3) variation in germination responses of seeds from different populations of the same species; (4) environmental factors that influence the mother plant, thereby causing changes in the germination characteristics of the progeny (seeds); (5) seed monomorphism and heteromorphism; (6) cleistogamy, amphicarpy, geocarpy and seed germination ecology; and (7) cleistogamous vs. chasmogamous seeds and their consequences on seedling recruitment. Also, the kinds of changes that can occur in seeds as they develop under varying environmental conditions are considered.

Professor Elsie Quarterman (1910–2014)

Dr. Elsie Quarterman, known fondly to her students as EQ, passed away on 9 June 2014 at her home in Nashville, Tennessee, at the age of 103 years. She was born on 28 November 1910 in Valdosta, Georgia. Dr. Quarterman obtained her B.A. degree from Georgia State Women’s College (now Valdosta State University) in 1932, after which she taught English in the Georgia public schools for 11 years. She obtained her M.A. degree in botany from Duke University in 1941 and her Ph.D. from the same institution in 1949. Her Ph.D. advisor was the renowned plant ecologist, Professor Henry J. Oosting. EQ’s M.A. degree was on the distribution of Compositae in Lowndes County, Georgia, and her Ph.D. degree was on the plant communities of the cedar glades of middle Tennessee. She published papers from her dissertation in The Bryologist (1949), Bulletin of the Torrey Botanical Club (1950), and Ecology (1950). Dr. Quarterman joined the faculty of Vanderbilt University as an instructor of biology in 1943 and was promoted through the academic ranks to professor in 1966. She served as chair of the Department of General Biology from 1961 to 1963, and retired from Vanderbilt in 1976, becoming Professor Emerita. In the academic world, Dr. Quarterman is best known for her work on the plant communities of the middle Tennessee cedar glades. She also is well known for the publication entitled ‘‘Southern Mixed Hardwood Forest: Climax in the Southeastern Coastal Plain, U.S.A.,’’ which she coauthored with her long-time friend, the late Dr. Catherine Keever and published in Ecological Monographs in 1962. Her first journal paper, entitled ‘‘A Preliminary Survey of the Bryophytes of Two Cedar Glades,’’ was published in The Bryologist in 1947. Her last paper, which she coauthored Dr. Quarterman with four of her former students. Back left, Jerry Baskin; back right, Tom Hemmerly; front left, Carol Baskin; middle, Dr. Quarterman; front right, Gail Baker

Biogeographical and Evolutionary Aspects of Seed Dormancy

The objective of this chapter is to formulate hypotheses concerning the origins and evolutionary relationships of the various types of seed dormancy. However, before significant hypotheses are generated, information is provided on various subjects. The subjects are world biogeography of seed dormancy types, and theoretical reasons why seed dormancy has evolved, and also paleoclimatic data. Next, it presents the record of embryos and seeds of fossils and phylogenetic position of families whose seeds have each type of dormancy. Moreover, it also provides fossil records at first appearance of families with each type of dormancy, and family tree of seed phylogeny, and type of embryo and the presumed age of the family. Morphological dormancy is never very important (maximum of 4% in temperate broadleaved evergreen forests), and it tends to be more common in both tropical/subtropical and temperate/arctic regions in vegetation types with the highest precipitation and temperatures, that is tropical rain forest, and temperate broadleaved evergreen forests, respectively. Morphophysiological dormancy is known in all types of species (trees, shrubs, lianas, herbs) in temperate broadleaved evergreen and deciduous forests, and in shrubs and herbs of steppe, matorral, and boreal vegetation, but only in herbs of cold deserts and tundra.

Germination Ecology of Plants with Specialized Life Cycles and/or Habitats

This chapter discusses the kinds of dormancy found in freshly matured seeds in each of the seven groups of plants. It discusses the available data on the environmental conditions required to break dormancy and stimulate germination. It also illustrates that parasites are organisms that obtain nutrients from another organism, called the host. However, parasitic flowering plants are divided into two groups such as holoparasites and hemiparasites. Holoparasites lack chlorophyll and receive fixed carbon, water, and minerals from the host plant, whereas, hemiparasites have chlorophyll and can fix carbon, but obtain water and minerals from the host. Little is known about the germination of seeds of mycoheterotrophs with the Pyroloid form of parasitism, except that seeds of Monotropa hypopithys that do not germinate unless the appropriate symbiont is present. As the number of seeds produced by parasitic plants increases, the possibility that some of them will reach a suitable host is enhanced. Physical dormancy is not known to occur in orchid seeds, and seeds of many species have been observed to imbibe water when placed on a moist substrate.