Organic matter quality of forest floor as a driver of C and P dynamics in acacia and eucalypt plantations established on a Ferralic Arenosols, Congo

Abstract Background Land-use change and forest management may alter soil organic matter (SOM) and nutrient dynamics, due in part to alterations in litter input and quality. Acacia was introduced in eucalypt plantations established in the Congolese coastal plains to improve soil fertility and tree growth. Eucalypt trees were expected to benefit from N2 fixed by acacia. However, some indicators suggest a perturbation in SOM and P dynamics might affect the sustainability of the system in the medium and long term. In tropical environments, most of the nutrient processes are determined by the high rates of organic matter (OM) mineralization. Therefore, SOM stability might play a crucial role in regulating soil-plant processes. In spite of this, the relationship between SOM quality, C and other nutrient dynamics are not well understood. In the present study, OM quality and P forms in forest floor and soil were investigated to get more insight on the C and P dynamics useful to sustainable management of forest plantations. Methods Thermal analysis (differential scanning calorimetry (DSC) and thermogravimetry (TGA)) and nuclear magnetic resonance (solid state 13C CPMASS and NMR and 31P-NMR) spectroscopy have been applied to partially decomposed forest floor and soils of pure acacia and eucalypt, and mixed-species acacia-eucalypt stands. Results Thermal analysis and 13C NMR analysis revealed a more advanced stage of humification in forest floor of acacia-eucalypt stands, suggesting a greater microbial activity in its litter. SOM were related to the OM recalcitrance of the forest floor, indicating this higher microbial activity of the forest floor in this stand might be favouring the incorporation of C into the mineral soil. Conclusions In relation with the fast mineralization in this environment, highly soluble orthophosphate was the dominant P form in both forest floor and soils. However, the mixed-species forest stands immobilized greater P in organic forms, preventing the P losses by leaching and contributing to sustain the P demand in the medium term. This shows that interactions between plants, microorganisms and soil can sustain the demand of this ecosystem. For this, the forest floor plays a key role in tightening the P cycle, minimizing the P losses

Soil organic matter quality along rotations in acacia and eucalypt plantations in the Congolese coastal plains

Abstract Background Afforestation of savannas in the Congolese coastal plains with eucalypt has provided wood pulp for industry and fuel energy for the local population. Typically, following afforestation, Acacia mangium are introduced to improve soil fertility and sustain productivity. Through investigations of particulate organic matter (POM), potential soil organic matter (SOM) quality was assessed in acacia and eucalypt plantations along rotations. Methods Nutrients in POM (4000–50 μm) in the 0–5 cm soil layer were measured after five years into the second rotation (R2Y5) in relation to soil pH and P availability. Data were compared to those at the end of the first 7-year-rotation (R1Y7) and after two years into the second rotation (R2Y2) to evaluate overall SOM quality in the topsoil. Results At R2Y5, soil pH was higher in the pure eucalypt stands (100E) than in stands containing acacia, either in monoculture (100A) or evenly mixed with eucalypt (50A50E). Coarse POM (cPOM, 4000–250 μm) beneath 100A had the highest N concentration (1.71%), followed by those beneath 50A50E (1.42%) and 100E (1.30%). Higher N was always found in the stands containing acacia. Lower sulphur (S) concentrations and P availabilities were observed in cPOM (50A50E). The greatest amount of coarse (414.7 g) and fine (214.5 g) forest floor litter were found in 100A stands, whereas higher C concentrations were found in the 100E stands for coarse forest floor litter (36.5%) and in the 50A50E stands for fine forest floor litter (38.7%). The decrease in cPOM N and C concentrations were lower than 20% (R1Y7) and 26% (R2Y5) relative to the younger stage (R2Y2). This tendency was more pronounced in fine POM (250–50 μm) and organo-mineral fraction (< 50 μm). Conclusions The main changes occurred in cPOM beneath stands containing acacia while higher weight of forest floor litter was found in 100A. Soil pH decreased in stands containing acacia. Overall N and C dynamics was enhanced in older stands (R2Y5) than in the younger stands (R2Y2). This may reveal a creation of more labile SOM with lower N and C concentrations in POM fractions in the surface layer, i.e., an ecosystem with a lower potential to mitigate climate change along rotations

The 4p1000 initiative : opportunities, limitations and challenges for implementing soil organic carbon sequestration as a sustainable development strategy

Authors would like to acknowledge the executive secretariat of the 4p1000 initiative, Charlotte Verger and Claire Weill for their valuable contributions during the preparation of this manuscript. The input of PS contributes to the UK NERC-funded Soils-R-GGREAT project (NE/P019455/1).Peer reviewedPostprin

The role of soil carbon sequestration in enhancing human resilience in tackling global crises including pandemics

International audienc

Sustaining Forest Plantations for the United Nations&rsquo; 2030 Agenda for Sustainable Development

Located in the hearth of Africa, the Congo basin is the world&rsquo;s second largest rainforest ecosystem, spanning over nine countries including the Republic of the Congo. Nature-based solutions, i.e., afforestation, reforestation or agroforestry supplying wood energy, halting food insecurity, restoring land desertification and fostering mitigation and adaptation to climate warming, have been increasingly used in the past decades. Within this framework, Congolese coastal plains have been afforested using fast growing trees since the early 1950s. Due to the low forest productivity and soil fertility, sustainable management of these forest ecosystems (trees, soils and environment) have been performed. Improved germplasms, increased stand wood biomass and healthier soils have the potential to enhance wood and fuel wood energy supply, mitigation and adaptation to climate change, food security, restoration of land and ecosystem biodiversity. This meets ten out of the seventeen sustainable development goals (SDG #), specifically goals related to alleviating poverty (1) and hunger (2), improving health (3), education (4), sanitation and access to clean water (6). Other goals include providing affordable clean energy (7), sustainable production and consumption (12), action on climate change (13), life on land (15), and partnerships for goals (17). Nature-based solutions help to face important societal challenges meeting more than half of SDGs of the United Nations

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

Soil has a major role in sequestering atmospheric CO2. This has further benefits and potential to improve soil fertility and food production, mitigate climate change, restore land degradation, and conserve ecosystem biodiversity. However, its health is increasingly being threatened by the growing population, land degradation and climate change effects. Despite its importance, soil organic carbon (SOC) is understudied in the tropics. This paper reviews how managing forests in tropical ecosystems can benefit SOC sequestration and land restoration. Sequestered SOC has the potential to improve soil fertility, as well as to reduce both land degradation and atmospheric CO2 emissions. It further improves soil structure, aggregation and water infiltration, enhances soil faunal activity and boosts nutrient cycling (C, N, P and S). Managing forest ecosystems is crucial to boost C sequestration, mitigate climate change and restore degraded lands, besides other ecosystem services they provide. Apart from managing natural forests and planted forests, afforesting, reforesting marginal or degraded lands especially when associated with specific practices (organic residue management, introducing nitrogen-fixing species) boost C storage (in both soil and biomass) and foster co-benefits as soil health improvement, food production, land restoration and mitigation of climate change. Improved soil health as a result of sequestered C is confirmed by enhanced physical, biological and chemical soil fertility (e.g., sequestered C stability through its link to N and P cycling driven by soil biota) which foster and sustain soil health

Dynamique de la matière organique en relation avec les propriétés chimiques et structurales des sols dans une chronoséquence forêt-prairies de graminées en Amazonie orientale (état de Para)

Studies of SOM changes along this forest-tc-pasture sequence were based on totalcarbon and 13C measurements, which allowed to calculate the distribution of carbon derived from forest and pasture throughout the profiles down to 1 rn depth. Carbon contents reached 116 Tha-l under forest and 12 year old pasture, 123 T ha-1 under 7 year pasture and 126 T ha-1 under 17 year old pasture. In the topsoil (0-0.10 rn) carbon derived from pasture increased from 12% in the 7 year old pasture to 38% in the 17 year old pasture. Moreover a degradation of physical-chernical properties was noted after pasture installation : the total porosity and rnacroporosity decreased in the topsoil, the storage porosity generally decreased, whereas the surface negative charges and clay dispersability increased in the 0-0,40m layers. Pasture establishment has induced an improvernent of aggregate stability in the topsoil, in relation with the change of SOM contents and nature and the increase of faunal activity such as earthworrns. In the topsoil, the changes of SOM quality was evaluated by a decrease of the proportion of light fraction (raw organic matter) and an increase of heavy fraction (organe-mineral macroaggregates) with increasing age of pasture. In addition, temporary increase of SOM biological and chernical s.tability was observed in the 7 and 12year old pastures.Après déforestation et installation des prairies dans des oxisols d'une chronosequence forêt-prairie de 7, 12 et 17 ans dans l'état de Para (Amazonie orientale), on a pu observer une légère augmentation de la quantité de carbone de 116 T ha-1(forêt) a 126 T ha-1(prairie de 17 ans). En revanche, les proportions du carbone d'origine graminéenne augmentent notamment en surface de 12 % sous prairie de 7 ans a 38 % sous prairie de 17 ans. Une dégradation des propriétés physico-chimiques est observée, se traduisant par une baisse de la porosité totale, de la porosité de stockage, tandis qu'une augmentation des charges de surface et de la dispersabilité des argiles est notée dans les couches organiques (0-0,40n) un accroissement temporairie de la stabilité chimique et surtout biologique de la matière organique de surface est observée sous prairies de 7 et 12 ans