Comparison of the Structure and Diversity of Root-Associated and Soil Microbial Communities Between Acacia Plantations and Native Tropical Mountain Forests.

Kozue Sawada,Koki Toyota,Mayuko Seki,Shinya Funakawa,Shinichi Watanabe,Hana Kobayashi,Ho Lam Nguyen,Soh Sugihara

doi:10.3389/fmicb.2021.735121

Abstract

Deforestation of native tropical forests has occurred extensively over several decades. The plantation of fast-growing trees, such as Acacia spp., is expanding rapidly in tropical regions, which can contribute to conserve the remaining native tropical forests. To better understand belowground biogeochemical cycles and the sustainable productivity of acacia plantations, we assessed the effects of vegetation (acacia plantations vs. native forests) and soil types (Oxisols vs. Ultisols) on soil properties, including the diversity and community structures of bacteria- and fungi-colonizing surface and subsurface roots and soil in the Central Highlands of Vietnam. The results in surface soil showed that pH was significantly higher in acacia than in native for Oxisols but not for Ultisols, while exchangeable Al was significantly lower in acacia than in native for Ultisols but not for Oxisols. Bacterial alpha diversity (especially within phylum Chloroflexi) was higher in acacia than in native only for Oxisols but not for Ultisols, which was the same statistical result as soil pH but not exchangeable Al. These results suggest that soil pH, but not exchangeable Al, can be the critical factor to determine bacterial diversity. Acacia tree roots supported greater proportions of copiotrophic bacteria, which may support lower contents of soil inorganic N, compared with native tree roots for both Oxisols and Ultisols. Acacia tree roots also supported greater proportions of plant pathogenic Mycoleptodiscus sp. but appeared to reduce the abundances and diversity of beneficial ECM fungi compared with native tree roots regardless of soil types. Such changes in fungal community structures may threaten the sustainable productivity of acacia plantations in the future.

Highlights

Tropical forests play important roles in biogeochemical cycling and global climate regulation, and are a major reservoir of biodiversity (Lee-Cruz et al, 2013)
To better understand belowground biogeochemical cycles and the sustainable productivity of acacia plantations, we investigated the effect of vegetation and soil types (Oxisols vs. Ultisols) on the diversity and structure of root-associated and soil bacterial and fungal communities in surface and subsurface horizons using a highthroughput amplicon sequencing technique
A significantly higher pH of mean 0.8 U was measured in acacia than in native for Oxisols, but no difference was observed for Ultisols (Table 1)

Summary

Introduction

Tropical forests play important roles in biogeochemical cycling and global climate regulation, and are a major reservoir of biodiversity (Lee-Cruz et al, 2013). Native tropical forests have undergone rapid clearance for agriculture (i.e., deforestation) over the past several decades (Gibbs et al, 2010; Hansen et al, 2013). Plantation of fastgrowing trees, such as Acacia spp., is expanding rapidly to meet the growing demand for wood (Chaudhary et al, 2016). The high productivity of acacia trees to produce large amounts of wood fiber for paper industries and charcoal for steel industries over a relatively short period can help to reduce the deforestation pressure on remaining native forests (Cossalter and Pye-Smith, 2003). Uncertainties remain about the sustainability of productivity of acacia plantations (Hung et al, 2016)

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Results

Discussion

Conclusion