This Journal of Environmental Horticulture article is reproduced with the consent of the Horticultural Research Institute (HRI – www.hriresearch.org), which was established in 1962 as the research and development affiliate of the American Nursery & Landscape Association (ANLA – http://www.anla.org). HRI’s Mission: To direct, fund, promote and communicate horticultural research, which increases the quality and value of ornamental plants, improves the productivity and profitability of the nursery and landscape industry, and protects and enhances the environment. The use of any trade name in this article does not imply an endorsement of the equipment, product or process named, nor any criticism of any similar products that are not mentioned. Copyright, All Rights Reserved Nodulation and Growth of Alnus nitida and Alnus maritima Inoculated with Species-specifi c and Nonspecifi c Frankia1 James A. Schrader and William R. Graves2 Department of Horticulture, Iowa State University, Ames, IA 50011-1100 Abstract Actinorhizal plants form N2-fi xing symbioses with soil-borne bacteria of the genus Frankia. Potential exists for development of sustainable, actinorhizal nursery crops that obtain most of their required N through N2 fi xation, but information on host-symbiont specifi city, presence of compatible Frankia in soils, and techniques to inoculate during plant production is lacking. Our objectives were to determine the effect of inoculum type and source and the effect of supplemental N on nodulation, growth, and N content of two actinorhizal species, Alnus nitida (Spach) Endl. and Alnus maritima (Marsh.) Muhl. ex Nutt. Plants of both species were subjected to one of four inoculum treatments (two crushed-nodule inocula: species-specifi c and cross inoculation, and two soil inocula: soil collected beneath native Alnus rubra Bong. in Washington state and native prairie soil from Iowa), were supplied fertilizer with or without N, and were grown in a greenhouse for 22 weeks. Inoculated plants nodulated, grew larger and faster, and accrued greater N content than uninoculated controls in both fertilizer treatments. Plants that received species-specifi c inoculum grew larger, acquired more dry weight from symbioses, and accumulated higher N content than cross-inoculated plants. Plants of A. nitida inoculated with soil from Washington state grew larger and accumulated more dry weight from symbioses than those inoculated with prairie soil, but A. maritima grew similarly with soil inoculum from both sources. Our results demonstrate that A. nitida and A. maritima can benefi t from N2-fi xing symbiosis during production and that potential exists for development of superior inocula and inoculation techniques. Index words: symbiotic nitrogen fi xation, actinorhizal plants, sustainable nursery production, plant-microbe interaction, host- symbiont compatibility and effi ciency. Species used in this study: Alnus nitida (Spach) Endl. (Himalayan alder); Alnus maritima (Marsh.) Muhl. ex Nutt. subsp. oklahomensis J.A.Schrad. & W.R.Graves (seaside alder, Oklahoma alder); Frankia Brunchorst spp. Signifi cance to the Nursery Industry are common in soils, but host specifi city affects symbiotic The need to develop sustainable nursery and landscape effi ciency. Superior symbioses can be formed by inoculation practices is of utmost importance due to unpredictable and with soils housing highly effective Frankia or with species- rising resource costs and the need to enhance ecosystem specifi c inoculum prepared from nodules of plants growing services [the benefi ts humans obtain from ecosystems (10)]. in native soils. These results provide important information Consumers continue to demand affordable, vigorous plants for the development of low-input production protocols for from the nursery industry, but environmental concerns actinorhizal nursery crops and provide basic knowledge have caused both producers and consumers to prefer cul- concerning host-symbiont specifi city and effi ciency in two tural practices that minimize environmental impacts. While promising actinorhizal taxa. consistent production of nursery crops has traditionally depended on high input of N fertilizer, which is costly both Introduction economically and environmentally, lower-input production Actinorhizal species are trees and shrubs that function methods must be developed for the industry to progress to- as pioneer plants on N-poor soils. Their potential to provide ward sustainability. N2-fi xing species have been utilized as much of their N requirements through N2-fi xing symbioses sustainable agronomic and vegetable crops for generations, with soil-borne Frankia bacteria makes them logical candi- but their potential as eco-friendly alternatives to high-input dates for development as sustainable crops for landscaping. nursery crops is just now being realized. The goals of our If attractive actinorhizal species can be selected and cultural research were to evaluate the capacity of actinorhizal spe- methods developed to maximize the benefi t of their N2-fi xing cies to provide for their N requirements through symbiotic symbioses, growers should be able to reduce N input during N2 fi xation and to determine the importance of inocula type, production. Of the more than 200 taxa known to form acti- species specifi city, and supplemental N for development of norhizal symbioses, species in the genus Alnus demonstrate effective N2-fi xing symbioses in seedlings of A. nitida and the highest rates of N2 fi xation and are worthy of increased A. maritima. Our results demonstrated that proper inocu- ornamental use (5, 6, 15, 33). Two autumn-blooming mem- lation of actinorhizal species can reduce their need for N bers of the genus, Alnus maritima (seaside alder) and Alnus input during production. Our fi ndings also indicated that nitida (Himalayan alder), are under horticultural evaluation Frankia strains compatible with A. nitida and A. maritima and are gaining in popularity. Alnus maritima, native to Okla- homa, Georgia, Maryland, and Delaware, is a stress-resistant, large shrub especially adapted to full sun and wet soils (9, 1Received for publication July 2, 2007; in revised form September 10, 29). Alnus nitida, native to India and Nepal, is the largest of 2007. We gratefully acknowledge the assistance and technical support of the alders, exceeding 30 m (98 ft) in height. With slightly M.S. Helgeson, R. Hummel, S.P. Kulshrestha, H.B. Naithani, A. Nakra, S.S. Samant, J. Sharma, Y.P. Singh, and the staff and students of B. Pant bluish leaves accented by red stems and twigs, its potential Institute of Himalayan Environment and Development, Himachal Unit, as a fast-growing landscape species is gaining recognition Mohal-Kullu, Himachal Pradesh, India. in Australia (14). The pendulous catkins of both species are 2Assistant Scientist and Professor, respectively. a unique and striking feature in autumn, and their persistent, J. Environ. Hort. 26(1):29–34. March 2008 29 cone-like strobili provide ornamental appeal during winter. collected from the roots of indigenous A. nitida growing west Ample genetic diversity exists within both species to facili- of the Beas River in Himachal Pradesh, India (31°53.048' N, tate plant breeding and cultivar selection (12, 27, 28). 77°05.204' E). In December 2005 nodules were collected Our objectives were to evaluate the potential for A. nitida from the roots of indigenous A. maritima growing along the and A. maritima to provide for their N requirements through Blue River in Johnston County, OK (34°19.589' N, 96°35.556' actinorhizal symbioses; to determine the effects of inocula W). Nodules were transported on ice to our research facility type and source on nodulation, growth, and N content of in Ames, IA, and crushed-nodule inoculum was produced plants; and to determine if supplemental N is essential for for each species by preparing a buffered slurry [phosphate proper growth and nodulation of young seedlings. While buffer, pH 7.3 (19)] that was mixed with fi ne vermiculite to symbionts of many N2-fi xing taxa are limited in geographic form a saturated inoculation medium. Control medium for distribution, Frankia compatible with Alnus spp. are believed this inoculum type was vermiculite saturated with distilled, to be both cosmopolitan and ubiquitous in soils, present even de-ionized water (dd H2O). Soil for the two treatments of in areas with no native Alnus spp. (2, 18, 20). Nonetheless, soil inocula was collected from the upper 20 cm (7.9 in) of Frankia are normally more abundant in soils where host the soil profi le from within the dripline of native A. rubra in plants are indigenous (3, 34), and Frankia strains capable of Pierce County, WA (47°10.634' N, 122°19.150' W) and from nodulating Alnus spp. vary in symbiotic effi ciency (11, 21, an undisturbed prairie site in Boone County, IA (Boone 36). To evaluate the importance of these issues in the sym- Prairie, 42°03.182' N, 93°49.358' W), devoid of actinorhizal bioses of A. nitida and A. maritima, we tested the nodulation species. Soil from the Washington site was used to help de- capacity and symbiotic effi ciency of Frankia from crushed termine if compatible Frankia are present in soils inhabited nodules of both species (species-specifi c and cross inocula- by Alnus spp. other than A. nitida and A. maritima. Prairie tion) and from two soils, one collected beneath indigenous soil was used to help determine if compatible Frankia are A. rubra in Washington state and one collected from an Iowa present in areas with no host plants. Control medium for the prairie devoid of actinorhizal species. soil inocula treatments was agricultural soil collected near Another factor that infl uences the establishment and ef- Ames, IA, and sterilized by autoclaving for 3 hours. Initial fi ciency of N2-fi xing symbioses is N content in the root zones N, P, and K contents of the three soils were analyzed at the of the host plants. High concentrations of N restrict nodule Soil and Plant Analysis Laboratory, Iowa State University, formation and activity in both legumes and actinorhizal spe- Ames, IA (Table 1).