United States Department of Agriculture Plant-Herbivore Interactions Forest Service in Atriplex: Current State of Rocky Mountain Research Station Knowledge General Technical Report RMRS-GTR-14 August 1998 Andrés F. Cibils David M. Swift E. Durant McArthur The Authors Research Summary Andrés F. Cibils has the degrees of Ingeniero Zootecnista The body of literature dealing with the biology of (1984) from the Universidad Nacional de Lomas de Atriplex is not only extensive and diverse, but is also Zamora in Buenos Aires, Argentina, and Master of Sci- scattered among a large variety of sources. The purpose ence in rangeland ecosystem science (1996) from Colo- of this review on plant-herbivore interactions in Atriplex rado State University. He is now a Ph.D. candidate at (saltbushes) was to gain insight into the ecology of Colorado State University, working on aspects of the browsed Atriplex stands. Our emphasis was bringing ecology of Atriplex canescens browsed by cattle in north- together and synthesizing research related to the use of eastern Colorado. He is presently on leave from the saltbushes as a browsing resource for ruminants. We Instituto Nacional de Tecnología Agropecuaria (INTA), took a broad view of the question and included most of where he holds a research position with the Natural the available literature relevant to the understanding of Resources Team of the Estación Experimental the complexities of saltbush-herbivore interactions. Agropecuaria Santa Cruz, Río Gallegos, Santa Cruz, This review is divided into five sections; the first four sections are divided into relatively self-contained sub- Argentina. He previously held the position of sections, allowing ready access to information of inter- Extensionist, also with INTA, in Puerto Deseado, Santa est. At the end of each of these sections is a brief Cruz, Argentina. synthesis of common elements in the literature reviewed David M. Swift is a Senior Research Scientist at the from an animal-plant interaction perspective. Natural Resource Ecology Laboratory and an Associate The first section discusses aspects of the physiological Professor in the Rangeland Ecosystem Science Depart- ecology and life history of Atriplex that help to understand ment, both at Colorado State University. He holds a B.S. why saltbushes have been used so extensively as a degree from the State University of New York, College of browse resource and also why the ecology of browsed Forestry, an M.S. degree in forest hydrology, and a Ph.D. stands may not be simple. The second section ad- degree in animal sciences, both from Colorado State dresses issues related to the effects of browsing on shrub University. His research included studies of productivity fitness, and survival and reproductive behavior of salt- and stability of traditional pastoral systems in East Africa, bushes subject to herbivory and water stress are its the ecology and nutrition of wild ruminants in Colorado, central topics. How saltbushes defend themselves against herbivory is dealt with in the third section, with special and techniques for measuring and estimating carrying emphasis on the literature related to saponins, a carbon- capacity for wild ungulates. He has a long standing based defense compound, common in saltbushes and interest in systems ecology and simulation of biological other chenopods. The fourth section discusses the ef- systems. fects that saltbushes have on the herbivores that con- E. Durant McArthur is Project Leader and Research sume them. Data both supporting and questioning the Geneticist for the Shrubland Biology and Restoration longstanding reputation that some saltbushes have en- Work Unit at the Rocky Mountain Research Station’s joyed as excellent forage are reviewed in detail in this Shrub Sciences Laboratory in Provo, UT. His degrees segment. In the fifth section we synthesize the informa- are from Dixie College, St. George, UT (A.S. in physical tion contained in the previous four sections, pointing out sciences, 1963) and the University of Utah (B.S. in potential interactions between ploidy level, breeding sys- molecular and genetic biology, 1965; and M.S., 1967, tem, defensive chemistry, and herbivory. and Ph.D. Degree, 1970, in plant genetics). He was a Postdoctoral Research Fellow in agricultural botany for Acknowledgments the Agricultural Research Council of Great Britain at the University of Leeds during 1970 and 1971. He began his While we were in the process of writing this publication Forest Service research career at the Great Basin Ex- we were able to talk to several of the authors of the papers perimental Range at Ephraim, UT, in 1972. He has been we reviewed, and in some instances to visit their re- at the Shrub Sciences Laboratory in Provo, UT, since search sites. We asked many questions about their 1975, and has been Project Leader since 1983. He has published work, and in every case encountered great generosity in sharing their information and time. We are held appointments as adjunct professor of botany and greatly indebted to them for the stimulation and help range science at Brigham Young University since 1976. they gave us. We also thank Drs. Terrance Booth, Bill Lauenroth, Dave Steingraeber, Darrell Ueckert, and Carl Wambolt for their valuable input on earlier versions of this manuscript. Rocky Mountain Research Station 324 25th Street Ogden, UT 84401 Contents Page Defense Theory, Dioecious Plants, and Page Atriplex ............................................................. 12 Introduction .............................................................. 1 Saponins: Chemical Characteristics and Aspects of the Physiological Ecology and Mode of Action ................................................. 14 Life History of Atriplex ........................................ 2 Saponins in Other Chenopodiaceae ................... 17 Environmental Conditions ..................................... 2 Nutritive Value of Atriplex as a Forage for Photosynthetic Pathways and Productivity ........... 2 Ruminants ....................................................... 17 Lifespan, Age Structure, and Patterns of Chemical Characteristics and Palatability ........... 17 Survival and Recruitment .................................. 4 Performance of Ruminants Fed with Ecotypic Variation and Polyploidy ......................... 5 Atriplex Diets ................................................... 20 Breeding Systems and Sex Expression ................ 6 Metabolic Alterations in Ruminants Effects of Browsing on Shrub Fitness ...................... 8 Consuming Atriplex ......................................... 21 Survival and Reproduction .................................... 8 Possible Management Implications of Browsing and Drought Effects ............................ 10 Herbivore-Atriplex Interactions ........................... 23 Differential Browsing of Individuals References ............................................................. 24 Within Populations ........................................... 11 Appendix: Index of Scientific and Common Defensive Chemistry of Atriplex ............................. 12 Plant Names ....................................................... 30 The use of trade or firm names in this publication is for reader information and does not imply endorsement by the U.S. Department of Agriculture or any product or service You may order additional copies of this publication by sending your mailing information in label form through one of the following media. 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CAUTION: Pesticides can be injurious to humans, domestic animals, desirable plants, and fish or other wildlife—if they are not handled or applied properly. Use all pesticides selectively and carefully. Follow recommended practices for the disposal of surplus pesticides and pesticide containers. Federal Recycling Program Printed on Recycled Paper Plant-Herbivore Interactions in Atriplex: Current State of Knowledge Andrés F. Cibils David M. Swift E. Durant McArthur Introduction ____________________ supplementary forage resource to feed small rumi- nants during periods of drought. Examples from the Saltbushes (Atriplex spp.) exhibit a series of out- literature point to work carried out in some African standing features—such as drought-hardiness, abil- countries (Egypt, Libya, Tunisia, Algeria, Morocco, ity to grow in saline and disturbed environments, Sudan, and South Africa), countries of the Middle East and tolerance to metal toxicity—that allow them to (Israel, Iraq, Syria, Iran, Yemen Arab Republic, and occupy a wide ecological range, spreading from ap- Saudi Arabia), Pakistan, Australia, and the United proximately 20 to 50 degrees latitude in both