Infectivity of soilborne Frankia and mycorrhizae in Discaria trinervis along a vegetation gradient in Patagonian soil

Abstract

The infective capacities of the nitrogen fixing Actinomycete Frankia and arbuscular mycorrhizal fungi from soils near watercourses, along a vegetation gradient, were studied using plant bioassays. Frankia and arbuscular mycorrhizas capable of infecting Discaria trinervis were found at seventeen sites sampled. More specific enumeration of the infective capacities of both microorganisms in relation to environmental factors was performed in seven representative soils of the analysed vegetation zones (rainforest, xeric forest and steppe) using the most probable number method. The highest nodulation capacities ranged from 340 infective units g(-1 )soil, in a steppe marsh devoid of actinorhizas, to 61 in a coastal actinorhizal scrub (in xeric forest). The highest number of infective mycorrhizal units--also found in marsh--was 145. In general, rainforest soils had the lowest values for both microorganisms. Infective units of Frankia and arbuscular mycorrhizal fungi in soil were positively correlated (r = 0.89, P < 0.05). Both soilborne symbionts showed the highest infective capacity in semi-arid conditions nearby watercourse and at the valley bottom location. Tripartite symbiosis was effective in plants inoculated with steppe and xeric forest soils and plants inoculated with Frankia BCU110501 and Glomus mosseae. Interaction between both symbionts and influence of environmental conditions, in general, would contribute to define comparable trends of their infective capacities.

Low Frankia inoculation potentials in primary successional sites at Mount St. Helens, Washington, USA

“…1). In alder thickets, where FIU density was greatest, the range of densities (0.43-2.1 IU/g) was comparable to those observed by Jeong and Myrold (2001) in Ceanothus velutinus-Douglas fir (Pseudotsuga menziesii) communities in the same region (range: 0.2 to 2.4 IU/g) and by Markham and Chanway (1996), but much lower than in some other studies (Chaia et al 2006;Maunuksela et al 1999;McCray Batzli et al 2004). These densities are low enough that in our growth experiment approximately 50% of seedlings remained un-nodulated at day 175, after inoculation with 3 g of this same soil.…”

Diversity of Plant Associated Actinobacteria

“…Nodulation unit (nu) per gram or per cm 3 soil is determined by nodulation capacity (NC) which is expressed as the number of Frankia particles per unit of soil, each of numbered Frankia induces one nodule in the nodulation test. Nodulation could also be determined by the MPN enumeration technique in which host plants are inoculated with serial dilutions of Frankia containing samples and formed nodules are enumerated Myrold et al 1994;Chaia et al 2006). Estimates by MPN were found to be in agreement with NC technique, especially between 30 and 300 nu g −1 soil, for Alnus infective Frankia (Huss-Danell and Myrold 1994).…”

Invasive Salix fragilis alters benthic invertebrate communities and litter decomposition in northern Patagonian streams

“…With regard to nutrient concentration, though we did not analyze leaf nutrients, species of the genus Salix and Ochetophila have symbiotic relationships with ecto-mycorrhizae and arbuscular mycorrhizae to promote the absorption of soil nutrients (Chaia, 1997;Hashimoto & Higuchi, 2003;Chaia et al, 2006). This relationship promotes high nutrient concentrations in leaves and roots, thus improving their nutritional quality for consumers and decomposers (Tortosa, 1983;Kull et al, 1998).…”