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

CHAIA E; FONTENLA S; VOBIS G; WALL LG

JOURNAL OF BASIC MICROBIOLOGY

Año: 2006 vol. 46 p. 263 - 274

0233-111X

The infective capacities of the nitrogen fixing Actinomycete Frankia and arbuscular mycorrhizal fungi from soils near watercourses, along a vegetation gradient, were studied by using plant bioassays. Frankia and arbuscular mycorrhizas capable to infect Discaria trinervis were found at 17 sites sampled. More specific enumeration of the infective capacities of both microorganisms in relation to environmental factors was performed in 7 representative soils of the vegetation zones analysed (rainforest, xeric forest and steppe) by 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 (located in the xeric forest). The highest number of infective mycorrhiza units was 145 and was also found in the marsh. In general, rainforest soils had the lowest values for both microorganisms. The 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 capacities in semi-arid conditions nearby to watercourses and at the location at the valley bottoms. Tripartite symbiosis was effective in plants inoculated with steppe and xeric forest soils and plants inoculated with Frankia BCU110501 and Glomus mosseae. The interaction between both symbionts and the influence of environmental conditions, in general, would contribute to define comparable trends of their infective capacities.