Effect of symbiotic associations on growth of host Coriaria nepalensis and its facilitative impact on oak and pine seedlings in the Central Himalaya M. Tiwari a,* , S.P. Singh a , A. Tiwari a , R.C. Sundriyal b a Department of Botany, Kumaun University, Tallital, Nainital, India b G.B. Pant Institute of Himalayan Environment and Development, North-East Unit, Itanagar, Arunachal Pradesh, India Received 4 March 2002; received in revised form 29 January 2003; accepted 23 March 2003 Abstract Effect of symbiotic association of actinorrhiza (Frankia) and arbuscular mycorrhiza on the seedling growth of host Coriaria nepalensis, and its facilitative effect on two important non-host seral tree species, i.e. oak (Quercus leucotrichophora) and pine (Pinus roxburghii) was studied. C. nepalensis showed dual symbiosis of actinorrhiza and arbuscular mycorrhiza. There was a significant increase in seedling growth of C. nepalensis when inoculated with arbuscular mycorrhiza compared with those inoculated with actinorrhiza. When seedlings of C. nepalensis were dual inoculated (with arbuscular mycorrhiza and actinorrhiza), improvement in growth was more than the sum of the individual effects of both symbionts. In dual inoculated C. nepalensis seedlings, arbuscular mycorrhiza also significantly increased nodule biomass. Actinorrhiza did not affect mycorrhizal status. The facilitative effect of C. nepalensis on the seedling growth of oak and pine was significant with arbuscular mycorrhiza, and among species the effect was more on pine than oak. The study reveals that the symbiotic association of microorganisms is useful not only to the host plant but also to neighbouring species, thus could be exploited for land rehabilitation in the scarce environment. # 2003 Elsevier B.V. All rights reserved. Keywords: Facilitation; Dual symbiosis; Mycorrhiza; Actinorrhiza; Coriaria nepalensis; Oak; Pine; Seedling growth 1. Introduction Major beneficial components of soil microbial com- munity are the symbionts in the form of mycorrhizal fungi and nitrogen fixing bacteria, which contribute to plant growth and survival by reducing stresses through symbiosis (Sylvia and William, 1992; Waaland and Allan, 1987; Madve, 1984). Leguminous and non-leguminous nitrogen fixing plants sometimes show symbiotic association with arbuscular mycor- rhizal fungi simultaneously with nodulating bacteria. The presence of these symbionts play a positive role in establishing and building plant community on dis- turbed sites as arbuscular mycorrhiza do increase the apparent size of the pool of soil nutrients (Ames et al., 1984; Barea et al., 1989). It indicates that mycorrhizal plants can either use available N forms more efficiently, or derive nutrients from sources less available to non-mycorrhizal plants. Since arbuscular mycorrhizal mycelia can extend to a long distance and can link the rhizosphere and mycorrhizosphere of Forest Ecology and Management 184 (2003) 141–147 * Corresponding author. Tel./fax: þ91-360-211773. E-mail addresses: mktiwari@hotmail.com (M. Tiwari), surps@yahoo.com (S.P. Singh), sundriyalrc@yahoo.com (R.C. Sundriyal). 0378-1127/$ – see front matter # 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0378-1127(03)00209-3