GERMINATION ECOPHYSIOLOGY OF HERBACEOUS PLANT SPECIES IN A TEMPERATE REGION

Germination phenology data have been collected from 75 winter annuals, 49 summer annuals, 28 monocarpic perennials, and 122 polycarpic perennials, and experimental investigations of dormancy breaking and germination requirements have been conducted on 56 winter annuals, 32 summer annuals, 18 monocarpic perennials, and 73 polycarpic perennials. The purpose of these studies was to determine if there are correlations between the dormancy breaking and germination requirements of seeds and the germination phenology, life cycle type, habitat requirements, range of geographical distribution, and phylogenetic relationships of the species. Germination phenology is highly correlated with the responses of seeds to the yearly temperature cycle. Species with winter and summer annual life cycles have predictable germination characteristics, but monocarpic and polycarpic perennials do not. Several dormancy types may be found in a given habitat, and narrowly endemic and widely-distributed species in the same genus may have similar germination characteristics. Within some families there is a tendency for a particular type of seed-temperature response to be very important, but frequently this is related to the predominance of a given life cycle type in the family. OUR FIRST STUDY of germination ecophysiology was undertaken as a project in Professor Elsie Quarterman's plant autecology class at Vanderbilt University in the spring of 1966. A literature search in connection with an investigation of the dormancy breaking and germination requirements of Aristida longespica and Sporobolus vaginiflorus (Baskin and Caudle, 1967) emphasized to us the need for studies on the germination ecology of mesic temperate herbs. Although many types of dormancy breaking requirements had been identified in seeds (Crocker, 1948; Crocker and Barton, 1957), this information had not been placed in context with germination phenology. Germination phenology had been described for a number of weed species (Bienchley and Warington, 1930; Chepil, 1946; Roberts, 1964), but not in respect to dormancy breaking and germination requirements of seeds. To determine how the timing of seed germination in herbaceous plants is controlled in nature, we combined descriptive studies of gerI Received for publication 26 January 1987, revision accepted 22 June 1987. From 1979 to 1985 part of our research was supported by grants from EPA (CR-806277-02) and USDA (82CRSR-21000) in connection with participation in the consortium for Integrated Pest Management (CIPM): Alfalfa Commodity. This support is gratefully acknowledged. This paper is dedicated to Dr. Elsie Quarterman, Professor Emeritus, Vanderbilt University, Nashville, TN. mination phenology with experimental studies of dormancy breaking and germination requirements. Numerous winter and summer annuals and monocarpic and polycarpic perennials were investigated, and these species were from various kinds of habitats including rock outcrops, fields, roadsides, pastures, mud flats, and deciduous forests. This is an ongoing effort; thus, while investigations of some species have been completed, other studies are in progress or being planned. To determine if there are correlations between the dormancy breaking and germination requirements of seeds and the germination phenology, life cycle type, habitat requirements, range of geographical distribution, and phylogenetic relationships of the species, it has been necessary to study many species. GERMINATION PHENOLOGY -Freshly-matured seeds, collected mostly from plants in Kentucky and Tennessee, were used to study germination phenology in a nontemperaturecontrolled greenhouse-no heating or air conditioning and windows open all year in Lexington, Kentucky. Temperatures in this greenhouse were similar to those in the field (Baskin and Baskin, 1981a; 1985b). Continuous thermograph records have been kept since October 1969, when phenology studies were started. From 1969 through 1972, studies involved four replications of 200 seeds each sown on the soil