Abstract
AbstractEndophytic fungi that asymptomatically colonize plants^1^ are diverse and abundant in tropical ecosystems^2^. These organisms can be weakly pathogenic^3^ and/or mutualistic, frequently enabling plants to adapt to extreme environments, alter competitive abilities of host individuals and improve host fitness under abiotic or biotic stresses^4,5,6^. Diplodia mutila is a symbiotic endophyte/plant pathogenic fungus infecting the palm Iriartea deltoidea^7^, which dominates many wet lowland Neotropical forests. The fungus is an asymptomatic endophyte in mature plants, and disease and mortality are expressed in some seedlings, while others remain disease free. Here we show that seedlings bearing the endophyte show enhanced resistance to insect herbivory. However, high light availability triggers pathogenicity of the fungus, while low light favors endosymbiotic development, constraining recruitment of endophyte-infested seedlings to the shaded understory by limiting survival of seedlings in direct light. These results provide evidence that patterns of plant abundance and the mechanisms maintaining tropical forest biodiversity are the result of a more complex interplay between abiotic and biotic environments than previously thought.
Highlights
Endophytic fungi that asymptomatically colonize plants diverse and abundant in tropical ecosystems 2. These organisms can be weakly pathogenic frequently enabling plants to adapt to extreme environments, alter competitive abilities of host individuals and improve host fitness under abiotic or biotic stresses a symbiotic endophyte/plant pathogenic fungus infecting the palm Iriartea deltoidea 7, which dominates many wet lowland
In this study we investigate the influence of a common pathogen-endophytic fungus, Diplodia mutila, on I. deltoidea survival and recruitment
This study found that Diplodia mutila is beneficial to the plant in understory conditions but strongly reduces the capacity of I. deltoidea to recruit in high-light forest gaps
Summary
In northeastern Peru 28 we arbitrarily placed 102 transects (5 x 500 m, divided in x 5 m subunits) located in mature primary tropical rain forest within 300 km of Iquitos, Peru (excluding transects located in secondary forests, white sand soils, steep topographical conditions and human disturbed forests). The total number of plants located in the 10 plots was 1068: 63 fruiting adults, 518 seedlings and 487 were considered juveniles-adults (non-fruiting). Plants located in the southeastern Peru plots were monitored for presence/absence of D. mutila and stem borers, three times after initial establishment (7, 50 and 150 days). The number of seedlings affected by stem borers and D. mutila was tallied for each 2.5 m annulus and divided by the total number of plants located in the selected annulus to yield proportions. In southeastern Peru light availability was estimated above the tallest photosynthetic leaf of each I. deltoidea seedling, using the average value of light intensity over the leaf with a light meter The total number of seedlings in the northeastern Peru transects was 660, 94% of seedlings were located at understory conditions (canopy scope
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