Michael Fenner

Seeds: the ecology of regeneration in plant communities

Reproductive allocation and reproductive effort in plants, F.A. Bazzaz and D.D. Ackerly maternal effects on seeds during development, Y. Gutterman the ecology of seed dispersal, M.F. Wilson animals as seed dispersers, E.W. Stiles fruits and frugivory, P. Jordano seed predators and plant population dynamics, M.J. Crawley longevity, viability and dormancy, A.J. Murdoch and R.H. Ellis the functional ecology of seed banks, K. Thompson seed responses to light, T.L. Pons the role of temperature in germination ecophysiology, R.J. Probert effect of chemical environment on seed germination, C.M. Karssen and H.W.M. Hilhorst the contribution of seedling regeneration to the structure and dynamics of plant communities and larger units of landscape, J.P. Grime and S.H. Hillier.

Reproductive allocation in plants

1. The Resource Economy of Plant Reproduction P. Staffan Karlsson and Marcos Mendez I. Introduction II. Historical Prelude III. The Principle of Allocation IV. Reproductive Effort A. Definitions V. Problems in Determining Reproductive Allocation A. The Currency B. Definition of Reproductive versus Non-reproductive Plant Parts C. When Should Reproductive Allocation be Measured? VI. Dynamic Resource Allocation VII. Empirical Patterns in Reproductive Allocation A. RA and Life History B. RA in relation to Succession, Competition and Disturbance C. RA in Relation to Environmental Stress D. Genetic Variation in RA E. What Does the Evidence Say? VIII. Costs of Reproduction A. Methodological Issues B. Quantitative Links Between Reproductive Allocation and Costs IX. Conclusions References 2. Meristem Allocation as a Means of Assessing Reproductive Allocation Kari Lehtila and Annika Sundas Larsson I. Abstract II. Introduction III. Developmental and Physiological Background of Meristem Allocation IV. Meristem Structure and Generation of Plant Architecture V. Axillary Bud Formation and Subsequent Development of the Bud VI. Genetics and Physiology of the Floral Transition VII. Meristem Types VIII. Meristem Models IX. The Assumptions of the Models X. The Impact of Meristem Allocation on Reproductive Allocation XI. Plasticity of Meristem Allocation XII. Major Genes of Meristem Allocation XIII. Resource Levels and Meristem Limitation XIV. The Function of Dormant Buds XV. Meristem Allocation as a Surrogate in Estimation of Resource Allocation XVI. Conclusions References 3. It Never Rains but then it Pours: The Diverse Effects of Water on Flower Integrity and Function Candace Galen I. Abstract II. Introduction III. The Functional Ecology of Water in the Life of a Flower A. Water Use by Flowers B. The Water Cost of Flowers C. Water as a regulator of Flower Microclimate D. Water as a conduit for Environmental Sources of Flower Damage IV. Water Relations and the Evolution of Floral Traits A. Floral Traits as Resource Sinks: The Resource Cost Hypothesis B. Floral Traits and Water in the Microclimate: Parental Environmental Effects C. Plastic Responses of Floral Traits to Water Availability: Impact on Plant/Pollinator Interactions V. Conclusions References 4. The Allometry of Reproductive Allocation Gregory Cheplick I. Introduction II. Definition and Analysis of RA in Relation to Allometry III. Allometry Theory and RA IV. Relation of RA to Relative Fitness V. Allometry of Modules VI. Allometry of RA and Plant Life History VII. Determinants of Allometry VIII. Conclusions References 5. Sex-Specific Physiology and Its Implications for the Cost of Reproduction Andrea L. Case and Tia-Lynn Ashman I. Introduction II. Sexual Polymorphisms III. Costs of Reproduction A. Male Costs B. Female Costs C. Common Flower Costs D. Demographic Costs IV. Avenues for Mitigating the Cost of Reproduction A. Photosynthetic Reproductive Organs B. Increased Vegetative Photosynthesis C. Increased Resource Uptake and Water Use Effeciency D. Resorption V. Predictions for Sex-Specific Physiology Based on Differential Reproductive Costs A. Predictions for Females and Males B. Predictions for Hermaphrodites in Monomorphic Sexual Systems: Cosexuality. Monoecy and Diphasy C. Predictions for Hermaphrodites in Dimorphic Sexual Systems: Gynodioecy and Subdioecy VI. Potential Causes of Sex-Specific Physiology A. Physiological Differences Reflect Plastic Responses to Contrasting Reproductive Allocation between Sexes B. Selection Modifies Physiological Traits after the Separation of the Sexes to Meet Differential Reproductive Costs C. Physiology Changes as a Correlated Response to Selection on Other Traits (e.g. via Pleiotropy or Linkage) VII. Available Data on Sex-Specific Physiology VIII. Recommendations for Future Study References 6. Time of Flowering, Costs of Reproduction and Reproductive Output in Annuals Tadaki Hirose, Toshihiko Kinugasa, and Yukinori Shitaka I. Introduction II. Modelling of reproductive output III. Timing of reproduction A. Effect of nutrient availability B. Effect of germination dates C. Effect of change in flowering time IV. Costs of reproduction A. Reproductive effort and the relative somatic cost B. Nitrogen use efficiency V. Reproductive nitrogen VI. Conclusion References 7. The Shape of the Trade-off Function between Reproduction and Growth Edward G. Reekie and German Avila-Sakar I. Introduction II. Methods of Describing the Trade-off Function III. The Shape of the Trade-off Function in Plantago IV. Impact of Reproduction on Resource Uptake V. Differences in the Resource Requirements of Vegetative versus Reproductive Tissue VI. Effect of Nitrogen versus Light Limitation VII. Effect of Growth Pattern VIII. Conclusion References 8. On Size, Fecundity and Fitness in Competing Plants Lonnie W. Aarssen I. Introduction II. Defining the Components of Competitive Ability for Between-Species Plant Competition III. Predicting Fecundity Under Competition IV. Relationships Among Plant Traits Affecting Fecundity Under Competition: Alternative Ways to Compete Intensively While Avoiding Competitive Exclusion V. Preliminary Empirical Tests VI. Predicting Winner from Rank Orders in Plant Competition: Lessons from Sports Competition VII. Conclusions

The phenology of growth and reproduction in plants

Abstract The study of phenological aspects of plants involves the observation, recording and interpretation of the timing of their life history events. This review considers the phenology of leafing, flowering and fruit production in a range of species and communities. The selective forces (both abiotic and biotic) that influence the timing of these events are discussed. Within the limits imposed by phylogenetic constraints, the phenological patterns (timing, frequency, duration, degree of synchrony, etc.) of each phase are probably the result of a compromise between a variety of selective pressures, such as seasonal climatic changes, resource availability, and the presence of pollinators, predators and seed dispersers. Many studies on flowering times stress the role of interactions between plant species which share pollinators or predators. The timing of fruiting plays a key role in controlling the abundance and variety of obligate frugivores in many tropical communities. The importance of long-term recording is stressed, particularly in species which fruit irregularly. An understanding of the phenology of plants is crucial to the understanding of community function and diversity.

An Experimental Field Study of the Effects of Mollusc Grazing on Seedling Recruitment and Survival in Grassland

1 The effect of mollusc herbivory on regeneration from seed was investigated for six common grassland species by sowing into artificially created gaps in a grassland sward. Molluscs were excluded from half the plots by application of molluscicide. 2 Samples taken monthly from October 1993 until March 1994 showed that species composition was markedly influenced throughout the study by the application of molluscicide. Plots from which molluscs were excluded contained significantly larger seedling numbers of Agrostis capillaris, Senecio jacobaea, Stellaria graminea, Taraxacum officinale and Trifolium repens while Ranunculus acris populations were unaffected by grazing. 3 Analysis of percentage cover during the final three months of the study, showed that the vegetation in ungrazed plots contained a significantly greater proportion of Agrostis, Stellaria, Taraxacum and Trifolium. In contrast, mean percentage cover of Senecio jacobaea and Ranunculus acris was significantly higher in grazed plots, in which Senecio accounted for up to 80% of the vegetation. 4 Significantly more Agrostis, Stellaria and Taraxacum inflorescences were recorded in ungrazed plots suggesting that mollusc herbivory influenced not only seedling survival, but also the fecundity of mature plants. Senecio and Ranunculus inflorescences were more frequent in grazed plots.

The effect of seedling age on the likelihood of herbivory by the slug Deroceras reticulatum.

1. The effect of seedling age on the risk of predation by molluscs was investigated for three common grassland species by exposing uneven-aged seedling assemblages (monoculture and mixed species) to grazing by the slug Derocerus reticulatum in experimental trays in greenhouse conditions. 2. In monoculture, seedling age was found to influence significantly the risk of mollusc attack on both Senecio jacobaea and Taraxacum offficinale. By contrast, the risk of attack on Veronica persica seedlings was unrelated to seedling age. 3. In a mixture of Taraxacum and Senecio seedlings, Taraxacum seedlings were not selected by slugs on the basis of age as they were in monoculture. Senecio seedlings in mixture with Taraxacum were generally grazed upon less than conspecifics in monoculture, although the effect of seedling age upon relative susceptibility to herbivory was broadly the same as in monoculture. 4. The results demonstrate that the timing of herbivory by molluscs can be crucial in determining the survivorship of a cohort of seedlings. The effects which seedling morphology, changes in seedling palatability with age, relative growth rates and pattern of association with neighbours have upon mollusc feeding behaviour are discussed, highlighting the role molluscs play as an important selective force in plant communities.

Pre-germination temperature and the survivorship and onward growth of Mediterranean fire-following plant species

Abstract The role of heat shock in the induction of seed germination for numerous Mediterranean fire-following plant species is well documented. However, the influence of pre-germination heating of seeds upon seedling survivorship and onward growth has not been studied. The aim of the experiments described here was to investigate how a range of heat treatments affects seedling survivorship and onward growth for six common fire-following Mediterranean plant species (Anthyllis vulneraria, Cistus creticus, C. salvifolius, Hippocrepis unisiliquosa, Pinus brutia and P. halepensis). In the first experiment, seeds of five species were heated to temperatures ranging between 80°C and 120°C (at 10°C intervals) for 10 min and subsequent seedling growth monitored over 8 weeks. Survivorship for two pine species (Pinus halepensis and Pinus brutia) was reduced after seeds were heated above 90°C. Onward growth for Pinus halepensis and the legume, Anthyllis vulneraria, was negatively affected by increasing pre-germination temperature. Survivorship and growth for both Cistus species was unaffected by heating seeds up to 110°C. The second experiment examined more closely seedling performance of Hippocrepis unisiliquosa seedlings when seeds were heated to temperatures ranging between 50°C and 90°C (at 10°C intervals) for 5, 10, 15 and 20 mins. Increasing pre-germination temperature and the length of time seeds were exposed to heating significantly reduced seedling growth rates in this species. The effect of fire on seedling emergence, growth and survivorship in the field is discussed with reference to the adaptation of the six species to post-fire regeneration and the patterns of seedling regeneration observed in the field.

The effect of mollusc grazing on seedling recruitment in artificially created grassland gaps

Two experiments conducted in spring and autumn 1992 examined the effect of mollusc grazing on seedling regeneration from natural grassland seedbanks by creating artificial gaps in plots in a grassland sward. Molluscs were excluded from half the gaps by application of molluscicide. Mollusc grazing in both the spring and autumn experiment significantly reduced seedling recruitment, though the intensity of grazing was greatest in autumn. Recruitment of five species was markedly influenced by molluscicide application. In spring, plots from which molluscs were excluded contained significantly more seedlings of Chenopodium polyspermum and Ranunculus acris. In the autumn, exclusion of molluscs resulted in increased populations of R. acris, Stellaria graminea and Rumex acetosa. Cerastium holosteoides populations were greatest in autumn grazed plots. Other species, notably the grasses Holcus lanatus and Agrostis capillaris and the legume Trifolium repens were unaffected by molluscicide application. Species diversity was significantly decreased by molluscicide application in the autumn. Gap size significantly affected the recruitment of two species. Ranunculus acris populations were significantly higher in small gaps in both spring and summer, while Chenopodium recruitment in the spring was greater in small gaps. Gap size also significantly influenced the risk of mollusc attack on Ranunculus as molluscs appeared to show an aggregative feeding response in the high seedling density small gaps. Selective grazing of vulnerable seedlings by molluscs may influence the eventual relative proportions of the species present and so provide a potent mechanism in shaping community composition in grasslands.

CHANGES IN DORMANCY LEVEL IN SORGHUM HALEPENSE SEEDS INDUCED BY WATER STRESS DURING SEED DEVELOPMENT

Dormancy in Sorghum halepense seeds as affected by intermittent water stress imposed on the mother plant during seed development was investigated. The drought treatment was imposed in cycles within the maturation period by with-holding water for 5 days, rewatering at the end of each drought cycle and withholding water again. The results showed that two sources of dormancy exist in S. halepense seeds: one is inherent in the caryopsis itself and is not affected by water stress during seed development (...)

Pregermination heat shock and seedling growth of fire-following Fabaceae from four Mediterranean-climate regions

The role of heat-shock in stimulating the germination of soil-stored seeds from fire-following plant species is well known. However, the effects of high pre-germination temperatures on subsequent seedling growth are less well understood. In this study, we examined the effect of pre-germination heat shock at five temperatures (60°, 75°, 90°, 105° and 120°C, each applied for 5 min) on the seedling growth of four, fire-following Fabaceae species from four Mediterranean-type ecosystems; Hippocrepis multisiliquosa (Israel), Gastrolobium villosum (Western Australia), Cyclopia pubescens (South Africa) and Lupinus succulentus (California). Following heat treatment and subsequent germination, seedlings were grown in controlled conditions before being harvested at either 10, 20- or 40 d old. A significant increase in mean dry weight biomass was found at 10 days for Hippocrepis seedlings germinated from seeds pre-heated to 90°C. However, subsequent comparison of mean dry weight biomass for seedlings of this species at 20 and 40 d old showed no significant response to heat shock pre-treatment. Similarly, an initial increase in growth of Gastrolobium seedlings germinated from seeds heated to 90° and 105°C disappeared as the plants matured. Seedling growth of Lupinus and Cyclopia was unaffected by the pre-germination heat treatment of their seeds. Since seedling competition is influenced by the size and growth rates of neighbouring plants, any changes in seedling growth rates as a consequence of the temperature environment experienced by their seeds, may therefore influence patterns of post-fire plant community recovery.

A bioassay to determine the limiting minerals for seeds from nutrient-deprived Senecio vulgaris plants

(1) The aims of this experiment were to determine which nutrient elements are most limiting to growth in newly-germinated seedlings of Senecio vulgaris dependent on their seed reserves, and how seedling nutrient-requirements are affected by the nutrient status of the parent plants. (2) Seeds were collected from plants which had been grown on a range of concentrations of Hoaglands full nutrient solution (20-100%). Seeds were also collected from plants growing in the field. (3) The seedlings were grown for three weeks in seven nutrient solutions, each of which had one macro-nutrient missing. These solutions lacked respectively nitrogen, phosphorus, potassium, calcium, magnesium, iron or sulphur. A control solution (containing a full nutrient supply) was also set up. (4) The final mean dry weight of the seedlings in each treatment was taken as a measure of their ability to rely on their internal supplies of each specific nutrient in the initial stages of growth. (5) Overall, the parental nutrient treatments had no significant effect on the seedling mineral requirements. (6) The most limiting elements in the seeds from the glasshouse parents were calcium and nitrogen and the least limiting were sulphur and iron. Phosphorus, potassium and magnesium were intermediate. Without nitrogen a seedling attained a dry weight of only three to five times that of the embryo; without sulphur it attained twenty-two to thirty-nine times the embryo weight. (7) Seedlings of the field-grown parents differed from those of the glasshouse parents in being generally larger and notably less limited by calcium and phosphorus. (8) The results indicate that the seedlings are more dependent on an external supply of certain mineral nutrients than others in the initial stages of growth. The balance of nutrients stored in the seeds of Senecio vulgaris is not related in any simple way to the apparent nutrient requirements of the seedlings.