Arbuscular mycorrhizae, a tool to enhance the recovery and re-introduction of Juglans venezuelensis Manning, an endemic tree on the brink of extinction

A pot experiment was conducted to evaluate the effects of two arbuscular mycorrhizal fungi (AMF), Dentiscutata heterogama and Rhizophagus manihotis on the growth and nutrition of Juglans venezuelensis Manning. This species is currently considered a threatened tree species and the successful restoration of its populations depends on an increased understanding of the ecological and physiological aspects of its response to inoculation with AMF. In general, shoot and total dry weight, and leaf area were significantly higher in seedlings inoculated with AMF than in non-inoculated ones. Differences in height and leaf number between the inoculated and non-inoculated treatments become apparent after 30 days of plant growth. Inoculated plants had a greater leaf area as the result of the higher allocation of resources to leaf biomass (leaf mass ratio, LMR). The fraction allocated to the roots (RMR) was not significantly different between treatments. Differences between vital stain (SDH) and non-vital trypan blue stain (TB) showed that the D. heterogama colonization was almost entirely active compared to the R. manihotis colonization. The relative responsiveness (RR) of J. venezuelensis to inoculation with D. heterogama and R. manihotis was 21.8 and 25.4 % respectively, but colonization values were never greater than 45 %, despite low P content in the soils used. The growth and physiological responses of J. venezuelensis to inoculation with two AMF species indicate that these microorganisms should be employed when propagating this threatened species for its subsequence reintroduction into its natural habitat.