Nodule-forming Sinorhizobium and arbuscular mycorrhizal fungi (AMF) improve the growth of Acacia farnesiana (Fabaceae): an alternative for the reforestation of the Cerro de la Estrella, Mexico

Background: Cerro de la Estrella (CE) is a natural reserve in Mexico City that suffers from afforestation, and its restoration with Acacia farnesiana is being considered . Question: Will the nodule-forming rhizobia and arbuscular mycorrhizal fungi (AMF) associated with the CE soil support A. farnesiana growth? Study species: Acacia farnesiana (L.) Willd . (Fabaceae). Methods: Mycorrhizal fungi, nodule-forming rhizobia and physicochemical characteristics of the CE soil were studied to determine if they are suitable for improving the growth of Acacia farnesiana . Results: Four different families of AMF were found which generated 13 % mycorrhization with A. farnesiana . However, A. farnesiana from CE did not nodulate, suggesting the lack of native rhizobia. The CE soil has low fertility. Nodules of A. farnesiana were obtained from the soil in Ticuman, Morelos, and 66 rhizobia were isolated from them. Rhizobium isolates were individually added to A. farnesiana grown in the CE soil. Five of the 66 isolates yielded significant differences in shoot dry weight, shoot height, number of nodules, nodulation time and nitrogenase activity compared with the Sinorhizobium americanum CFNEI 156 control strain ( p < 0.05). Three isolates were named as S. americanum ENCBTM1, ENCBTM31 and ENCBTM43, and last two as Sinorhizobium sp. ENCBTM34 and ENCBTM45. Conclusions: CE soil had low fertility and lacked specific rhizobia for A. farnesiana . The individual addition of S. americanum (ENCBTM1, ENCBTM31 or ENCBTM43) or Sinorhizobium sp. (ENCBTM34 or ENCBTM45) improved the growth of A. farnesiana.