Influence of Two Important Leguminous Trees on Their Soil Microbiomes and Nitrogen Cycle Activities in a Primary and Recovering Secondary Forest in the Northern Zone of Costa Rica

Inga edulis and Pentaclethra macroloba are dominant N-fixing forest trees in Costa Rica, likely important for recovery of soil N and C after deforestation, yet little is known of their soil microbiomes nor how land use impacts them. Soils from both trees in a primary and secondary forest were assessed for N-cycle metrics and DNA sequence-based composition of total bacterial, potential N-fixing bacterial, and potential ammonium oxidizing bacterial genera. The compositions of the functional groups of bacteria, but not their total relative abundance of DNA, were different across the soils. The P. macroloba soils had greater NO3− levels and richness of both functional groups, while I. edulis soils had greater NH4+ levels, consistent with its NH4+ preference for root nodule development. The bacterial communities were different by habitat, as secondary forest I. edulis microbiomes were less rich, more dominant, possibly more affected by the disturbance, or reached equilibrium status quicker than the richer, less dominant P. macroloba microbiomes, which may be developing slower along with secondary forest succession, or were less affected by the disturbance. Functional redundancy and switching of 10 N-cycle bacterial genera was evident between the primary and secondary forest soils, likely to maintain stable levels of N-cycle activity following disturbance. In summary, the two tree soil microbiomes are different, land use differentially affects them, and, thus, both tree species should be used during forest regeneration strategies in this region.

Morphological aspects and anatomy of the fruit, seeds and seedlings of Pentaclethra macroloba (willd.) Kuntze (Fabaceae)

The aim of this study was to describe the morphology of fruit, seeds and seedlings, as well as the anatomy of the seed and the seedling of Pentaclethra macroloba (Willd.) Kuntze. Morpho-biometry was performed on fifty fruit samples and one hundred seeds. To describe the sequences of the morphological events of the germination stages, ten seeds were placed to germinate. Anatomical analysis was performed in a scanning electron microscope with seed samples and seedling leaves. The species has leguminous type fruit of 16.1 to 45.2 cm length and 4.1 to 7.3 cm width; seeds have a pleurogram and are eurispermic, ovoid, deltoid to elliptical and measure from 3.8 to 6.1 cm length and 2.5 to 5.7 cm width. Anatomically, the cotyledons are composed of thin-walled parenchyma cells with various oil cells. The seedlings have bipinnate leaves, with waxes and simple trichomes at the margins of the adaxial surface and paracytic stomata on the abaxial surface. The epicotyl is slightly twisted, with caducous cataphylls and a first pair of alternate eophylls. Germination is of the phanero-hypogean-reserve type. Taxonomic recognition of this species is possible in the field through the external morphological traits and can help in identification of saplings.

La respuesta compensatoria de Pentaclethra macroloba ante tratamientos antagónicos: la fertilización y la defoliación

La combinación de rasgos como la fijación de nitrógeno en plantas tropicales con otros rasgos como disponibilidad nutricional podría incidir en el éxito de algunas especies para su establecimiento y desarrollo. Otras interacciones como la herbivoría podrían cambiar sutilmente estas relaciones y llegar a ser relevantes para su éxito ecológico. Sometimos brinzales de Pentaclethra macroloba (Gavilán, Fabaceae) en macetas, con y sin adición de nutrientes y a la interacción con defoliación controlada (herbivoría artificial), en el sotobosque secundario dentro de un bosque de Sarapiquí, Costa Rica. La biomasa total muestra una fuerte compensación neta y la defoliación indujo una mayor asignación al follaje. La fertilización siempre resultó en menos asignación a nódulos. La esbeltez respondió a ambos factores de manera sinergística. Sugerimos que la herbivoría puede ocasionar cambios importantes en la manera en que las especies asignan sus recursos en concordancia con sus simbiosis y la disponibilidad de nutrientes.