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

William D Eaton,Katie M Mcgee,Mehrdad Hajibabaei,Elizabeth Hoke,Alex Lemenze

doi:10.3390/soilsystems4040065

Abstract

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.

Highlights

Deforestation for agricultural uses has long been occurring in tropical regions such as the NorthernZone of Costa [1,2], resulting in diminished rates and levels of activity of soil nitrogen (N) and carbon (C) cycle dynamics and related soil ecosystem conditions, and the colonization of scrub growth or invasive species rather than development healthy secondary forests [1]
Our conclusions are that: (a) P. macroloba and I. edulis stimulate the development of different soil microbiome assemblages; (b) differences in these microbiome are driven by the different the Land Management practice of Secondary Forest development used in this region; (c) I. edulis soils had a less rich but more evenly distributed total bacterial soil microbiome that may have been more impacted by the land use practice or may be developing more slowly than that of
The differences found in the in bacterial communities between the tree soil microbiomes, the greater levels of NO3 − -related metrics, and the reduced levels of NH4 + -related metrics found in the P. macroloba soils, and the opposite found in the I. edulis soils, suggests P. macroloba soil microbiomes are more critical for producing NO3 −, and the I. edulis microbiomes more critical for producing NH4 + into these forest soil ecosystems

Summary

Introduction

Deforestation for agricultural uses has long been occurring in tropical regions such as the NorthernZone of Costa [1,2], resulting in diminished rates and levels of activity of soil nitrogen (N) and carbon (C) cycle dynamics and related soil ecosystem conditions, and the colonization of scrub growth or invasive species rather than development healthy secondary forests [1]. 2020, 4, 0065 in high demand for the rapidly growing vegetation during reforestation [11] To remediate these disturbed soils and forested areas, secondary forest regeneration following different types of land use damage is becoming common in these regions [2,12,13,14]. Little is known of the ecological relationships between these leguminous trees, their soil ecosystems, or their soil N-cycle-associated microbiome communities It is unclear how land management or other disturbances and restoration activities impact the overall soil ecosystem conditions, the composition or recovery of the soil N-cycle microbial communities, or even how these impacts might influence rates of regrowth of tropical forests. This information could provide insights useful in maximizing the efficacy of tropical forest and soil restoration and recovery plans [22,23,24,25,26,27]

Methods

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Discussion

Conclusion