Elsevier

Pedosphere

Volume 33, Issue 3, June 2023, Pages 508-520
Pedosphere

Soil bacterial communities under slash and burn in Mozambique as revealed by a metataxonomic approach

https://doi.org/10.1016/j.pedsph.2022.06.053Get rights and content

Abstract

The slash-and-burn system is a subsistence agronomical practice widespread in tropical areas worldwide. This system has been extensively studied, especially for its impacts on agronomical aspects and soil physicochemical properties; however, knowledge of soil microbial diversity under slash and bum is scarce. In this study, for the first time, soil bacterial diversity of three locations from Central Mozambique, where slash and burn has been practiced for different durations of the forest fallow period (ca. 25, 35, and 50 years), was elucidated through a metataxonomic approach. Bacterial communities were evaluated in the genetic horizons of soils under charcoal kilns, crop fields, and forests. The aim of this study was to examine the influence of spatial (location and land use), temporal (forest fallow period), and vertical (horizon) variations on bacterial community structure in relation to soil physicochemical properties. Metataxonomic analysis detected 25 different phyla whose distribution varied horizontally and vertically in relation to soil properties (i.e., pH, easily oxidizable organic carbon, total nitrogen, and available phosphorus), as well as particle size distribution and mineralogical composition. Such properties were strongly affected and altered by land-use management; in particular, charcoal kilns exhibited better soil properties and greater differences in bacterial community than crop fields and forests, which were quite similar. This might suggest the inability of a forest fallow period shorter than 50 years to improve soil fertility and induce changes in bacterial community. The uncommon application of the pedological approach for microbial evaluation facilitated the detection of a clear separation in bacterial composition along the soil profile, with eutrophic bacteria mainly located in the A horizon whereas oligotrophic bacteria were found in the Bo horizon. These horizontal and vertical heterogeneities in the same study represent a novelty for bacterial metataxonomic analysis.

Section snippets

INTRODUCTION

The agroforestry system known as “slash and burn” is largely practiced by smallholder farmers in tropical and subtropical regions (Mertz et al., 2009; Erni, 2015; Kukla et al., 2019). It refers to occupying a piece of land and slashing and burning the vegetation to convert forests into agricultural fields (Gay-des-Combes et al., 2017a). During the conversion, ephemeral charcoal kilns (3−6 ha−1) are arranged to produce charcoal for the family. Thus, after 2−4 years of cultivation, the area is

Study areas

The zone selected for the study is part of Manica Province, Central Mozambique (Fig. S1, see Supplementary Material for Fig. S1). Here, we selected three locations with high agricultural potential where slash-and-burn practices are very common and have been ongoing for centuries: Vanduzi, Sussundenga, and Macate (Fig. S1). Based on the climatic conditions, soil type, elevation, and farming system, these districts are located in Agro-Ecological Zone R4, which includes lands 200−1 000 m above sea

Soil morphology

At all locations (Vanduzi, Sussundenga, and Macate), the soils were Oxisols because of the presence of diagnostic Bo horizon (Soil Survey Staff, 2014) (Table SI). The A horizons under the charcoal kilns showed a charcoal content always > 30%, whereas the charcoal contents were ca. 1% in the crop fields and under detection limit in the forests. The Bo horizons showed a reddish color and, especially at Vanduzi, displayed a relatively high content of iron (Fe)-manganese (Mn) oxides (ca. 5%). In

Location effect

The three locations showed different bacterial relative abundances for several taxa. In detail, the Actinobacteria were dominant in the soils of Vanduzi. The Actinobacteria phylum has been widely reported in soils under various environmental conditions, including those in Antarctica and Sahara (Saker et al., 2015; Tytgat et al., 2016); it is probably the wide adaptability of the species belonging to this phylum that resulted in its high relative abundance in the soils of Vanduzi. Araujo et al.

CONCLUSIONS

Oxisols subjected to slash and burn differed in terms of the spatial and vertical changes in their bacterial diversity. Soil bacteria were affected by soil physicochemical properties reliant on both soil genesis and human activity. Actinobacteria, Nitrospirae, WS3, Chloroflexi, Verrucomicrobia, Planctomycetes, and Firmicutes varied among locations in conjunction with different soil pH levels and nutrient availabilities, whereas the Cyanobacteria abundance seemed to depend on soil quartz

ACKNOWLEDGEMENTS

The authors acknowledge the help of the Sussundenga Agrarian Research Station from the Instituto de Investigação Agrária de Moçambique (IIAM) and, specifically, Mr. Domingos Feniasse for leading our team during the field work and Mr. Alcídio Vilanculos for his help during the field work, mainly with vegetation description and species identification. The authors would like to thank Dr. Nicola Butani of Polytechnic University of Marche, Italy, for his support in the molecular biology analysis. We

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