The Botanical Review 63(1)

Interpreting Botanical Progress

	Azolla:  A Review of Its Biology and Utilization
	   Gregory M. Wagner..........................................1

	Roles of Flavonoids in Symbiotic and Defense Functions
	in Legume Roots
	   Helen A. Stafford.........................................27

	River Dynamics as a Forest Process: Interaction between
	Fluvial Systems and Alluvial Forests in Large European
	River Plains
	   Annik Schnitzler..........................................40

	Sexual Specialization and Inbreeding Avoidance in the
	Evolution of Dioecy
	   D. Carl Freeman, Jon Lovett Doust, Ali El-Keblawy, 
	    Kathleen J. Miglia,  and E. Durant McArthur..............65
	Instructions to Contributors.................................93

	New Books Received...........................................96

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	Published Quarterly by
	The New York Botanical Garden
	Issued 31 March 1997

Azolla: A Review of Its Biology and Utilization
Department of Zoology and Marine Biology
University of Dar es Salaam
P.O. Box 35064
Dar es Salaam
		I. Abstract
	       II. Introduction
	      III. Taxonomy
	       IV. Distribution
		V. Morphology
	       VI. Physiology
	      VII. Reproduction
	     VIII. Environmental Factors Affecting Azolla Anabaena
	       IX. The Utilization of Azolla Anabaena
		       A. Azolla Anabaena as a Biofertilizer
		       B. The Utilization of Azolla Anabaena on Rice
		       C. The Application of Azolla Anabaena on Crops Other Than Rice
		       D. Other Uses of Azolla Anabaena
		X. Concluding Remarks
	       XI. Acknowledgment
	      XII. Literature Cited
I. Abstract
The symbiosis Azolla Anabaena is outstanding due to its high productivity combined with its ability to fix nitrogen at high rates. Because of this, in recent decades, countless studies have been conducted on this association, but with insufficient synthesis and coordination. This paper, therefore, attempts to review and synthesize past and recent findings concerning the biology and utilization of Azolla in hopes that this will facilitate increased future collaborative research on this "green gold mine." It reviews the taxonomy, distribution, morphology, physiology, and reproduction of Azolla as well as new developments in its manifold uses.Because of the growing concern about conservation of the environment and the need for deploying renewable, sustainable resources; the application of Azolla as a biofertilizer on agricultural crops, in order to provide a natural source of the crucial nutrient nitrogen, can be very beneficial to the future of our planet. Besides the environmental appropriateness of the use of Azolla, for multitudes of farmers in many parts of the world who cannot afford chemical fertilizers, Azolla application can enhance their economic status, increasing yields while minimizing costs. Due to the fact that rice paddy fields form an ideal environment for Azolla, one of its most suitable applications is on rice. Besides its utilization as a biofertilizer on a variety of crops, Azolla can be used as an animal feed, a human food, a medicine, and a water purifier. It may also be used for the production of hydrogen fuel, the production of biogas, the control of weeds, the control of mosquitoes, and the reduction of ammonia volatilization which accompanies the application of chemical nitrogen fertilizer. Click Here to Go to Back to Top Roles of Flavonoids in Symbiotic and Defense Functions in Legume Roots HELEN A. STAFFORD Biology Department, Reed College Portland, Oregon 97202 I. Abstract II. Introduction III. Flavonoids in Nodules IV. Arbuscular Mycorrhizal Fungal Relationships V. Model Legume Genomes VII. Structural and Regulatory Genes of Root Symbioses VIII. Conclusions IX. Literature Cited
I. Abstract
The roles of flavonoids in roots of legumes in the symbiotic relationships with nitrogen-fixing bacteria and arbuscular mycorrhizal fungi are compared with defense functions, using examples from three legume genera, Lotus, Medicago and Glycine. Pathways leading to proanthocyanidins and isoflavonoids are emphasized. The localization of flavonoids in nodules involved in nitrogen-fixation and in the apoplastic compartment of mycorrhizal associations is briefly described, with emphasis on the need for more information concerning their precise localization. The limitation of our knowledge about the regulatory genes of the flavonoid pathway involved in both exogenous and endogenous regulation of these complex interrelationships is emphasized. Click Here to Go to Back to Top River Dynamics As a Forest Process Interaction between fluvial systems and alluvial forests in large European river plains. ANNIK SCHNITZLER Laboratoire de Phytoécologie Faculté des Sciences Ile du Saulcy, F-57045 Metz, France Tél. (33) 03 87 31 53 31 Fax: (33) 03 87 31 53 33 I. Abstract/Résumé II. Introduction III. The Geomorphic Pattern of Big River Plains IV. Particularities of the Nutrient Cycle V. Specific Particularities A. Species Abundance and Diversity B. Community Pattern and Forest Dynamics C. The Particular Case of Riverine Ecosystems of High Dynamics Rivers VI. Conclusion VII. Literature Cited
I. Abstract
This paper corresponds to an overview of the impacts of the inundatons on gallery forest processes, with examples of the upper Rhine valley, France. The geomorphic pattern of big river plains, the particularities of the nutrient cycle, the adaptations of the flora, the specificities of the sylvigenetic cycles are detailed, with examples of the upper Rhine valley, where the author has worked over more than 10 years. Key-words: river, Rhine, fluvial, processes forest, species richness, complexity.
Cet article se propose de passer en revue les impacts majeurs des rivières sur les forêts riveraines, avec des exemples pris essentiellement dans la vallée du Rhin, en France; que l'auteur a étudiée pendant plus de 10 ans. Les adaptations de la flore et les spécificité des cycles sylvigénétiques sont mis en relation avec les particularités géomorphologiques et celles du cycle biogéochimique particulier au milieu alluvial. Click Here to Go to Back to Top

Sexual Specialization and Inbreeding Avoidance in the Evolution of Dioecy

D. Carl Freeman                            Jon Lovett Doust
Department of Biological Sciences          Department of Biological Sciences
Wayne State University                     University of Windsor
Detroit, MI 48202, U.S.A.                  Windsor, Ontario, Canada N9B 3P4            
Ali El-Keblawy                             Kathleen J. Miglia
Department of Biology                      Department of Biological Sciences
University of Suez Canal                   Wayne State University
El-Arish, Egypt                            Detroit, MI 48202, U.S.A.
		       E. Durant McArthur
		       Shrub Sciences Laboratory
		       U.S. Department of Agriculture Forest Service
		       Provo, UT 84606, U.S.A.
		 II. Introduction 
		III. Animal-Pollinated Plants
		      A. Hermaphroditism
		      B. Potential for Inbreeding
		      C. Avoidance of Inbreeding
		      D. Sexual Specialization in Hermaphrodites
		      E. Sexual Specialization and Sexual Dimorphism
		      F. Sexual Specialization in Resource Allocation
		 IV. Abiotic Pollination
		      A. Potential for Inbreeding
		      B. Potential for Compensation and Sexual 
		  V. Pathways for the Evolution of Dioecy
		      A. Dioecy from Gynodioecy
		      B. Summary of Gynodioecy Pathway and Predictions
		      C. Dioecy from Monoecy
		 VI. Spatial Niche Segregation of the Sexes
		VII. Sexual Lability
	       VIII. Case Studies of Species Showing Labile Sex
		       Expression and Intermediate Sex Forms
		 IX. Analysis of Patterns, and Resolution of 
		       Competing Hypotheses for the Evolution of Dioecy 
		      A. Theoretical Considerations
		  X. Conclusion
		 XI. Acknowledgments
		XII. Literature Cited
I. Abstract
Dioecy has evolved independently, many times, among unrelated taxa. It also appears to have evolved along two contrasting pathways: (1) from hermaphroditism via monoecy to dioecy and 2) from hermaphroditism via gynodioecy to dioecy. Most dioecious plants have close cosexual relatives with some means of promoting outcrossing (e.g., herkogamy, dichogamy, self- incompatibility, or monoecy). To the extent that these devices prevent inbreeding,the evolution of dioecy in these species cannot logically be attributed to selection for outcrossing. In these cases, the evolution of dioecy is, we believe, due to selection for sexual specialization. However, in other species, that lack outbreeding close relatives, dioecy may have evolved from gynodioecy (males and hermaphrodites) as an outbreeding device. Subsequent disruptive selection and selection for sexual specialization may have also shaped the evolution of dioecy from gynodioecy in these species, resulting in two genetically determined, constant sex morphs. Both pathways for the evolution of dioecy require the operation of disruptive selection, though the gynodioecy route involves more restrictive disruptive selection and a genetic designation of gender. In contrast, the monoecy route is not dependent on the genetic designation of two sex morphs, but, rather, allows the possibility of sexual intermediates and sexual lability. Both pathways produce one morph in which maleness is uppressed and another in which the female function is negligible or nonexistent the reproductive mode recognized as dioecy. Evidence is presented here to support the thesis that instances of sexual lability, the presence of an array of sexual intermediates, sex-switching, and sexual niche segregation can be explained in terms of the pathway that was taken in the evolution of a particular dioecious species. In addition, the degree of sexual dimorphism seen in dioecious species is correlated with mode of pollination (insect- or wind-pollinated) and other ecological factors. Click Here to Go to Back to Top