Influence of Acacia mangium on Soil Fertility and Bacterial Community in Eucalyptus Plantations in the Congolese Coastal Plains

Abstract

Productivity and sustainability of tropical forest plantations greatly rely on regulation of ecosystem functioning and nutrient cycling, i.e., the link between plant growth, nutrient availability, and the microbial community structure. So far, these interactions have never been evaluated in the Acacia and Eucalyptus forest planted on infertile soils in the Congolese coastal plains. In the present work, the soil bacterial community has been investigated by metabarcoding of the 16S rRNA bacterial gene in different stands of monoculture and mixed-species plantation to evaluate the potential of nitrogen-fixing trees on nutrient and bacterial structure. At the phylum level, the soil bacterial community was dominated by Actinobacteria, followed by Proteobacteria, Firmicutes, and Acidobacteria. A principal coordinate analysis revealed that bacterial communities from pure Eucalyptus, compared to those from plantations containing Acacia in pure and mixed-species stands, showed different community composition (beta-diversity). Regardless of the large variability of the studied soils, the prevalence of Firmicutes phylum, and lower bacterial richness and phylogenic diversity were reported in stands containing Acacia relative to the pure Eucalyptus. Distance-based redundancy analysis revealed a positive correlation of available phosphorus (P) and carbon/nitrogen (C/N) ratio with bacterial community structure. However, the Spearman correlation test revealed a broad correlation between the relative abundance of bacterial taxa and soil attributes, in particular with sulfur (S) and carbon (C), suggesting the important role of soil bacterial community in nutrient cycling in this type of forest management. Concerning mixed plantations, a shift in bacterial community structure was observed, probably linked to other changes, i.e., improvement in soil fertility (enhanced P and C dynamics in forest floor and soil, and increase in soil N status), and C sequestration in both soil and stand wood biomass with the great potential impact to mitigate climate change. Overall, our findings highlight the role of soil attributes, especially C, S, available P, and C/N ratio at a lesser extent, in driving the soil bacterial community in mixed-species plantations and its potential to improve soil fertility and to sustain Eucalyptus plantations established on the infertile and sandy soils of the Congolese coastal plains.

How hydrogen sulfide deposition from oil exploitation may affect bacterial communities and the health of forest soils in Congolese coastal plains?

“…Human well-being and challenges are linked to four out of 17 sustainable development goals (SDG) of the United Nations (Sustainable Development Goals: 17 Goals to Transform our WorldUnited Nations): SDG 2: end hunger, achieve food security, improve nutrition, and promote sustainable agriculture; SDG 3: ensure healthy lives and promote well-being for all at all ages; SDG 13: take urgent action to combat climate change and its impacts; and SDG 15: protect, restore, and promote sustainable use of terrestrial ecosystems; sustainably manage forests; combat desertification; halt and reverse land degradation; and halt biodiversity loss. (49,51). No difference has been noticed regarding the Actinobacteria, which harbors prevalence in all studied stands, i.e., in the monoculture acacia and eucalyptus and mixed-species stands (50% acacia and 50% eucalyptus) (51).…”

“…(49,51). No difference has been noticed regarding the Actinobacteria, which harbors prevalence in all studied stands, i.e., in the monoculture acacia and eucalyptus and mixed-species stands (50% acacia and 50% eucalyptus) (51). This may have further boosted its growth and biomass, as commonly found in industrial areas (49), and enhanced organic material dynamics since Actinobacteria play a key role in decomposing organic materials (50).…”

“…Along with changes in soil organic matter quantity and quality, enhanced activity of edaphic macroarthropod communities through the dominance of ants in eucalyptus against cockroaches in acacia litter has been reported in mixed-species forest plantations of the Congolese coastal plains (17). More than two decades later, bacterial community composition reported Actinobacteria as the dominant phylum in all stands, with Firmicutes as the second prevalent phylum in stands containing acacia and Proteobacteria in monoculture of eucalyptus (51). Anthropogenic activities affect the environment, i.e., both terrestrial and/or marine ecosystems, and may impact the soil microbiome, e.g., its richness and/or diversity and soil health (36,40,41,43,55,56).…”

“…Albeit there is no difference in Actinobacteria, the prevalent phylum among stands, both its prevalence and strong correlation to sulfur (S) have been noticed at all levels of the taxonomy using metabarcoding of the 16S rRNA bacterial gene. In addition, a shift in the bacterial community composition was evidenced by the dominance of Proteobacteria in eucalyptus monoculture against Firmicutes in stands containing acacia (51). Therefore, further studies are needed to confirm this trend.…”

Does the Introduction of N2-Fixing Trees in Forest Plantations on Tropical Soils Ameliorate Low Fertility and Enhance Carbon Sequestration via Interactions Between Biota and Nutrient Availability? Case Studies From Central Africa and South America

“…Sustaining forest plantations strongly relies on interactions among nutrient cycling, microbial communities and environment (54). Using meta-barcoding of the 16S rRNA bacterial genes, the predominance of Actinobacteria phylum, strongly correlated to sulfur (S) at all classes, has been observed in different stands of monoculture and mixed-species plantations in the Congolese coastal plains (55). This may be due to the potential impact of H 2 S deposition from oil exploration activities (from the end of the 1960s) on the environment i.e., the bacterial communities (Koutika, personal communication).…”