Growth responses and N and P use efficiency of three Alnus species as affected by arbuscular-mycorrhizal colonisation

Abstract

In this study it was determined how different species of Alnus (A. cordata, A. incana and A. glutinosa) responded to colonisation by arbuscular mycorrhizal (AM) fungi (Glomus mosseae or Glomus intraradices) with regard to growth and their ability to acquire and utilise nitrogen and phosphorus. Non-mycorrhizal plants but with phosphorus added, were used as control. In A. glutinosa the application of 75 ppm P had similar effect on growth and P acquisition as did AM. Nevertheless, A. cordata and A. incana grew poorly when supplied with 75 ppm of P and required AM symbiosis for optimum growth and N and P uptake. The percentage increases in shoot dry biomass in AM colonised as compared with P-fertilised plants were 441 (A. cordata) and 644 (A. incana) whilst AM-colonised A. glutinosa matched P-fertilised plants. Plant shoot N/P ratio increased in response to AM-colonisation indicating that mycorrhizal effects on N uptake are greater than on P uptake. Information concerning the direct influence of AM on N acquisition and nutrient use efficiency by Alnus species is important. AM-colonisation provides an excellent biological mechanism by which Alnus plants became more efficient P-users. That Alnus sp. are highly mycorrhizal-dependent plants was apparent because AM-colonisation was critical for growth of A. incana and A. cordata. In this respect, for maximizing the efficient uptake and use of N and P, under the growth conditions provided, Alnus plants need to be mycorrhizal. AM symbiosis seems decisive for the successful establishment of Alnus sp. in revegetation strategies. The low N and P availability in soils where Alnus species are useful candidates in any recolonisation and reclamation process emphasises the need to investigate systems by which N and P uptake by Alnus plants can be enhanced.