Tree species and soil nutrients drive tropical reforestation more than associations with mycorrhizal fungi

Abstract

The relative benefits that mycorrhizal fungi confer to host plants and reforestation efforts may differ due to the host tree species and soil nutrient status. Our research objective was to examine the effects of mycorrhizal fungi, host tree species, and soil nutrient availability on nutrient acquisition in tropical reforestation. Four tree species (Pinus caribaea, Quercus insignis, Swietenia macrophylla, and Terminalia amazonia) were planted across eight sites and subjected to five nutrient treatments in southern Costa Rica. After two years, there were strong growth differences based upon tree species but not mycorrhizal fungi. Site variation, specifically base cation availability, and nutrient treatments also influenced tree growth and tissue nutrient concentrations. In a complementary greenhouse experiment isolating fungal from tree species effects, the ratio of nutrients in treatments was more important to tree growth responses to fungal symbionts than individual nutrients. These results show that soil nutrient availability may be more important to tree species’ nutrient acquisition than mycorrhizal fungi. This study highlights the importance of tree species selection and replication across sites with different soil nutrient ratios in order to make management recommendations for reforestation success.