Symbiotic relationships of Alnus glutinosa with arbuscular mycorrhizal fungi and with Frankia

The occurrence in Scotland of arbuscular mycorrhizal fungi (AMF) infective on Alnus glutinosa and the effects on early growth of inoculation of seedlings with AMF and Frankia were investigated. AMF characteristic of G/omiw-like fungi were detected microscopically in A. glutinosa roots from mineral and loam but not from highly organic soils. Both GJomusand Gigaspora-like fungi were detected only in roots from sandy soils. Glasshouse experiments showed that Glomus and Gigaspora species gave higher colonisation of roots, and were of higher compatibility with the host plant, than Acutelospora or Scutettospora species. Colonisation by AMF increased nodulation by Frankia and vice versa. Inoculation with AMF alone and dual inoculation with Gigaspora rosea and Frankia inhibited growth of young A. glutinosa seedlings. Initially after inoculation, AMF colonisation was poor allowing the host to meet the requirements of both developing symbioses. Mycorrhizal plants inoculated with Frankia 15 days after AMF inoculation, were under significant stress and this delayed the beneficial effects of AMF and Frankia symbiosis. Seedlings compensated for the cost of symbiosis by developing a larger, leafy shoot in a period of 25-30 days after AMF inoculation, with or with out, Frankia nodulation. A significant increase in root length and branching detected after inoculation with AMF and Frankia must impose additional energy requirements. However, the stimulation of lateral root branching that follows AMF colonisation may facilitate nutrient uptake, thus helping the plant to overcome the disadvantages of early retardation of shoot growth. Competition with adjacent plant species for below ground space may also be enhanced thus facilitating competition for growing space with other plant species. These factors may be part of a strategy that assists the survival of very young seedlings in the field. The data obtained suggest that delaying Frankia inoculation for 3-4 weeks after inoculation with selected AMF should improve the production in Scottish nurseries of robust, well nodulated and mycorrhizal seedlings. CONTENTS 1.INTRODUCTION. 13 1.1 The actinorhizal symbiosis . 15 1.2 Mycorrhizal symbiosis. 19 1.2.1 Orchid mycorrhizas. 21 1.2.2 Ericoid mycorrhizas. 21 1.2.3 Ectomycorrhizal (EMF)symbiosis.21 1.2.4 Arbuscular mycorrhizal (AMF) symbiosis. 23 1.2.5 Root colonisation and arbuscular mycorrhizal development.26 1.3 Mycorrhizal interactions with the host plant and Frankia. 29 1.4 Aims of study.36 2. MATERIALS AND METHODS.37 2.1 Preliminary screening of roots ofAlnus glutinosa from the field for AMF. -37 2.2 Baiting experiments to determine the occurrence in the field of Frankia, EMF and AMF infections ofAlnus glutinosa. 38 2.2.1 Germination of seed. 3 8 2.2.2 Soil collection and soil analysis. --. -39 2.2.3 Experimental design.39 2.2.4 Ectomycorrhizal and arbuscular mycorrhizal colonisation and Frankia nodulation.39 2.3 Effects of colonisation with different AMF species on Alnus glutinosa growth . 40 2.3. 1 Germination of seed. 40 2.3. 2 AMF culture.40 2.3. 3 Experimental design.40 2.3. 4 Seedling harvest and preparation analysis for analysis . 41 2.3. 5 Arbuscular mycorrhizal colonisation.42 2.3. 6 Mineral element analysis (N, P). 43 2.3. 7 Statistical analysis. 43 2.4 Effects of AMF on growth of Alnus glutinosa receiving additional mineral nutrients.44 2.4. 1 Germination of seed.44 2.4. 2 AMF culture.44 2.4. 3 Experimental design. 44 2.4. 4 Seedling harvest and preparation for analysis . 46 2.4. 5 Colonisation by AMF.46 2.4. 6 Mineral element analysis (Hf). 46 2.4. 7 Statistical analysis. -. -. 46 2.5 Interactions between AMF and Frankia during early stages of the establishment of symbiosis with Alnus glutinosa. 46 2.5. 1 Germination of seed. -46 2.5. 2 Frankia culture. 47