Glime, J. M. 2017. Ecophysiology of development: Gametophores. Chapt. 5-5. In: Glime, J. M. Bryophyte Ecology. Volume 1. 5-5-1 Physiological Ecology. Ebook sponsored by Michigan Technological University and the International Association of Bryologists. Last updated 11 April 2021 and available at <http://digitalcommons.mtu.edu/bryophyte-ecology/>. CHAPTER 5-5 ECOPHYSIOLOGY OF DEVELOPMENT: GAMETOPHORES TABLE OF CONTENTS Growth ................................................................................................................................................................ 5-5-2 Stem Growth ....................................................................................................................................................... 5-5-2 Water ............................................................................................................................................................ 5-5-3 Light ............................................................................................................................................................. 5-5-4 Tropisms ...................................................................................................................................................... 5-5-6 Photoperiod .................................................................................................................................................. 5-5-7 Temperature ................................................................................................................................................. 5-5-7 Growth Regulators ....................................................................................................................................... 5-5-8 Branches and Apical Dominance ...................................................................................................................... 5-5-11 Environmental Factors ............................................................................................................................... 5-5-13 Growth Regulators ..................................................................................................................................... 5-5-14 Pleurocarpous Mosses ......................................................................................................................... 5-5-15 Thallose Liverworts ............................................................................................................................ 5-5-16 Nutrients ..................................................................................................................................................... 5-5-17 Leaves ............................................................................................................................................................... 5-5-17 Light ........................................................................................................................................................... 5-5-17 Water .......................................................................................................................................................... 5-5-18 Nutrients ..................................................................................................................................................... 5-5-20 Growth Regulators ..................................................................................................................................... 5-5-21 Liverwort Leaf Suppression ................................................................................................................ 5-5-22 Cuticle ........................................................................................................................................................ 5-5-23 Rhizoids ............................................................................................................................................................ 5-5-23 Temperature ............................................................................................................................................... 5-5-24 Light ........................................................................................................................................................... 5-5-25 Tropisms .................................................................................................................................................... 5-5-26 Adhesion .................................................................................................................................................... 5-5-28 Growth Regulators ..................................................................................................................................... 5-5-28 Wounding ................................................................................................................................................... 5-5-29 Habitat Conditions ..................................................................................................................................... 5-5-30 Conduction ................................................................................................................................................. 5-5-33 Bryophyte Senescence ...................................................................................................................................... 5-5-33 Ecological Interaction ....................................................................................................................................... 5-5-33 Summary ........................................................................................................................................................... 5-5-34 Acknowledgments ............................................................................................................................................. 5-5-35 Literature Cited ................................................................................................................................................. 5-5-35 5-5-2 Chapter 5-5: Ecophysiology of Development: Gametophores CHAPTER 5-5 ECOPHYSIOLOGY OF DEVELOPMENT: GAMETOPHORES Figure 1. Bryum pseudotriquetrum gametophores, showing leaves, stems, and rhizoids. Photo by Janice Glime. Growth Stem Growth Bryophytes appear to be simple plants, but if one Stem growth in plants occurs primarily as a result of changes perspective, you might agree with Renzaglia et al. cell elongation, which is sometimes accompanied by cell (2000) that these gametophytes "are the most elaborate of division (Bidwell 1979). Cell elongation occurs by a those produced by any land plant." In mosses, it is the apex loosening of the side walls of the cell to allow expansion. of branches or stem tips that ultimately develop into Auxin helps to loosen the wall but exogenous calcium and reproductive organs. This contrasts with flowering plants ethylene inhibit loosening (Ray et al. 1983) (probably that develop their gametophyte without archegonia and because Ca forms Ca pectate, which glues cell walls antheridia, reducing the male gametophyte to a pollen grain together). Loosening is followed by an uptake of water by and the female gametophyte to a partitioned embryo sac the cell, which is an osmotic response to increase of Ca within the female sporangium (sporophyte tissue). within the cell. The increased turgor then expands the cell. In mosses and leafy liverworts, gametophore The turgor can be affected by mineral nutrients, development can be considered a four-part process: stem photosynthesis, respiration, transpiration, ethylene, water growth, branch production, leaf development, and rhizoid availability, temperature, etc. If any of these factors formation (Figure 1). Since these four processes must becomes limiting, it can inhibit stem elongation. compete for energy, it is expected that they are, at least in When measuring growth, one consideration must be most cases, distinct events with different environmental what to measure. When a layperson thinks of growth, it is stimuli or optima. usually equated with increase in height, but in biological Chapter 5-5: Ecophysiology of Development: Gametophores 5-5-3 terms it can include branching and weight gain as well. When growth is promoted, energy is diverted from Measuring extension in height gets complicated by the fact other events. This diversion can manifest itself as a result that if light intensity is insufficient, cells will extend with of a change in environmental conditions. For example, little or no weight gain, and often at a greater than normal when grown in red light, Ceratodon purpureus (Figure 4) rate – the etiolation effect (Figure 2). This is especially a exhibited only 20% branching with a weight gain of 16.8 problem in laboratory experiments where light intensity is mg per 50 individuals, but when the plants were grown usually considerably below that in nature, even compared under far-red illumination, there was 100% branching, but to some forested settings. Plants, including bryophytes, only 11.75 mg weight gain per 50 plants (Hoddinott & Bain become thin, weak, and lose their green color. In this case, 1979). This would appear to be counter-intuitive until one false implications of growth occur. This can easily be seen recognizes that while the branches were growing, the plants when bryophytes are collected and kept in a sealed plastic in far-red light were also producing setae, thus diverting