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

Abstract

Plant and/or crop growth rely on nutrient dynamics driven by specific soil biota in different environments. This mini-review aims to provide an overview of interactions between soil organisms, nutrient dynamics, and C sequestration. To this end, we investigated published results from three forest plantations (eucalyptus monocultures and mixed plantations with N2-fixing acacia) on tropical nutrient-poor soils. One case study is located in Central Africa (Congolese coastal plains) and two others in South America (Southeastern Brazil). Overall, the studies showed that soil biota activity exerted positive effects on (i) C accretion, as both soil carbon and belowground and aboveground biomass are driven and enhanced by soil biota; and (ii) on nutrient dynamics and biogeochemical cycles in nutrient-poor soil of tropical ecosystems, which are boosted following C accumulation. On the other hand, the pedoclimatic environment may potentially impact soil functioning of mixed-species plantations through its influence on the composition and activity of bacterial communities. Regardless of the potential risk of acacia invasiveness, benefits such as pulp, fuelwood, electric pole and non-timber products supply, have been reported in Central Africa. We, therefore, conclude that including N2 fixing trees in forestry plantations as reported in this mini-review helps strengthen the links between soil biota, nutrient and SOC dynamics in mixed-species plantations on tropical nutrient-poor soils.

Boosting C Sequestration and Land Restoration through Forest Management in Tropical Ecosystems: A Mini-Review

“…This is due to biological changes that result from newly added organic residues [74,75] or the input of N-rich organic matter following the shift in the microbial activity and/or bacterial composition [76][77][78][79][80]. Changes in soil microbial indicators lead to C and N accumulation in eucalypt mixed with acacia stands relative to pure or fertilized stands after 27 months [15]. In fact, N 2 -fixing species have the ability to ameliorate soil fertility and enhance carbon sequestration via interactions between biota and nutrient availability in tropical forest plantations [15,69,77,78].…”

“…Changes in soil microbial indicators lead to C and N accumulation in eucalypt mixed with acacia stands relative to pure or fertilized stands after 27 months [15]. In fact, N 2 -fixing species have the ability to ameliorate soil fertility and enhance carbon sequestration via interactions between biota and nutrient availability in tropical forest plantations [15,69,77,78].…”

“…Amongst these tropical forest ecosystems, there are three main rainforest basins, i.e., the Amazon basin being the largest, the Congo basin and Southeast Asia the second and third, respectively [14]. Managing forest in these regions is, therefore, vital to foster C sequestration with further benefits on land restoration (degraded forests and other lands), mitigating climate change and preserving natural forests and ecosystem biodiversity [15].…”

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

“…These plantations may also have the potential to enhance soil sulfur concentrations, which appear to be two to three higher than commonly observed (28), since although considered an essential plant nutrient, soil S concentration is only about 10% of that of the total N (29). Benefits have also been reported through C sequestration in soil (6,19) and increased stand wood biomass, i.e., forest productivity (21,30), that boost the potential to mitigate climate change through increased C stocks (6,14,31). Soil habitat, i.e., its diversity, regulates the conservation and productivity of ecosystems (32).…”

“…Actinobacteria harbor a high ability to decompose a broad range of hydrocarbons, pesticides, and feather waste (50). Increased C and N stocks at 7 years of the first rotation of forest plantations (stands containing acacia, 19, 22) and phosphorus availability (afforested stands, 23) may be related to prevalence of Actinobacteria determined using metabarcoding of the 16S rRNA bacterial gene (31). Besides, H 2 S resulting from natural processes and enabling the presence of Actinobacteria (48), the prevalence of Actinobaceria may result from human activities (31,49) and potentially benefit to soil attributes such as C and P dynamics.…”