nitrogen fixation in acacias CORE Metadata, citation and similar papers at core.ac.uk Provided by Research Papers in Economics Many a tree is found in the wood, And every tree for its use is good; Some for the strength of the gnarled root, Some for the sweetness of fl ower or fruit. Henry van Dyke, Salute the Trees He that planteth a tree is the servant of God, He provideth a kindness for many generations, And faces that he hath not seen shall bless him. Henry van Dyke, Th e Friendly Trees Nitrogen Fixation in Acacias: an Untapped Resource for Sustainable Plantations, Farm Forestry and Land Reclamation John Brockwell, Suzette D. Searle, Alison C. Jeavons and Meigan Waayers Australian Centre for International Agricultural Research 2005 Th e Australian Centre for International Agricultural Research (ACIAR) was established in June 1982 by an Act of the Australian Parliament. Its mandate is to help identify agricultural problems in developing countries and to commission collaborative research between Australian and developing country researchers in fi elds where Australia has a special research competence. Where trade names are used, this constitutes neither endorsement of nor discrimination against any product by the Centre. aciar monograph series Th is series contains results of original research supported by ACIAR, or deemed relevant to ACIAR’s research objectives. Th e series is distributed internationally, with an emphasis on developing countries. © Australian Centre for International Agricultural Research 2005 Brockwell, J., Searle, S.D., Jeavons, A.C. and Waayers, M. 2005. Nitrogen fi xation in acacias: an untapped resource for sustainable plantations, farm forestry and land reclamation. ACIAR Monograph No. 115, 132p. 1 86320 489 X (print) 1 86320 490 3 (electronic) Editing and design by Clarus Design, Canberra Foreword Acacias possess many useful attributes — they are Over the past two decades, Australian scientists adapted to a wide range of warm-temperate and and their counterparts in partner countries have tropical environments including arid and saline sites, pursued the domestication of acacias through a and infertile and acid soils. Th e species most used in wide range of studies. Important outcomes include a forestry come from Australia or nearby countries, greater understanding of both the acacias and their but others in cultivation are from India, Myanmar, symbiotic micro-organisms, and the development of Arabia, Africa, tropical America and Hawaii. techniques for exploiting effi cient symbioses. Th ese developments are summarised in this review. Although acacias have been an important element of agricultural systems in Africa for centuries, more We compliment the authors of this publication. extensive cultivation commenced after Australian Th eir account is a valuable compilation of widely species were introduced into India for fuelwood dispersed information, enhanced by their capacity around 1850, and later to southern Africa for to assess its merit and relevance. Th ey conclude tanbark production. Th is latter role subsequently that improved nitrogen fi xation is a potential diff used, on a smaller scale, to other countries bonus whenever acacia is cultivated, and that including Brazil and China. the magnitude of the bonus will depend on both eff ective inoculation and good silviculture. Some hundred years later, the cultivation of acacias has again blossomed. Tropical species are attracting ACIAR is pleased to continue its strong support for attention for their potential to provide wood for the domestication of these important trees through industrial and domestic purposes, and the use of a the publication of this review. Th e publication is also variety of species for land rehabilitation, especially available on ACIAR’s website at <www.aciar.gov.au>. in Australia, is expanding rapidly. Th e ability of legumes to fi x atmospheric nitrogen effi ciently has been exploited with conspicuous success in agriculture — pastures based on Peter Core, Director, Australian Centre for subterranean clover are a notable Australian International Agricultural Research example. Such successes, and the prominence of acacias in many natural ecosystems, have fuelled hopes that eff ective nitrogen fi xation by cultivated acacias would enhance the growth of both the acacia Alan Brown, Honorary Research Fellow, CSIRO and associated crops. Forestry and Forest Products 5 Contents Foreword ....................................................................................................................................5 Dedication .................................................................................................................................9 Preface ..................................................................................................................................... 11 Acknowledgments .............................................................................................................. 13 Abstract ................................................................................................................................... 15 1. Introduction .................................................................................................................... 17 2. Th e plant ............................................................................................................................ 18 Utilisation .............................................................................................................................. 19 Distribution ........................................................................................................................... 24 Plant taxonomy ...................................................................................................................... 24 Root and nodule morphology ............................................................................................... 28 3. Th e bacteria ...................................................................................................................... 29 Acacia rhizobia in nature ....................................................................................................... 29 Taxonomy of acacia rhizobia ................................................................................................. 31 Diversity of acacia rhizobia ...................................................................................................34 Comment on the taxonomy and diversity of acacia rhizobia .............................................. 36 Root infection and nodule formation ...................................................................................36 Rhizobial products ................................................................................................................. 37 7 nitrogen fixation in acacias 4. Th e symbiosis .................................................................................................................. 39 Measurement of nitrogen fi xation ....................................................................................... 41 Consideration of procedures for measuring N fi xation .......................................................43 Nitrogen fi xation in glasshouse and nursery ....................................................................... 44 Nitrogen fi xation in the fi eld ................................................................................................ 45 Environmental factors aff ecting nitrogen fi xation in the fi eld ........................................... 49 Mycorrhizal factors aff ecting nitrogen fi xation in the fi eld ................................................ 58 Rhizobial factors infl uencing nitrogen fi xation in the fi eld ................................................ 60 5. Enhancement of the symbiosis ............................................................................... 69 Th e need for inoculation ........................................................................................................69 Responses to rhizobial inoculation of acacias in fi eld and nursery .................................... 69 Inoculants .............................................................................................................................. 72 Breeding and selection for enhanced acacia symbiosis ....................................................... 77 6. Exploitation of the symbiosis .................................................................................. 78 Natural exploitation .............................................................................................................. 78 General exploitation .............................................................................................................. 79 Intercropping ......................................................................................................................... 79 Land reclamation: principles and practice — the Australian experience ............................82 7. General conclusions and prognosis ....................................................................... 89 Th e plant ................................................................................................................................. 89 Th e bacteria ............................................................................................................................ 90 Th e symbiosis ........................................................................................................................