Biogeochemistry of dissolved organic matter and inorganic solutes in soil profiles of tropical pasturelands

Author(s)

dos Santos, Joao Vitor ; Goranov, Aleksandar I. ; Bento, Lucas R. ; Oliveira, Patricia P. A. ; Pezzopane, Jose R. M. ; Bernardi, Alberto C. C. ; de Sa, Ivero P. ; Nogueira, Ana Rita A. ; Martin-Neto, Ladislau ; Hatcher, Patrick G.

• Document type: Journal article
• Source: SOIL & TILLAGE RESEARCH; v. 240, p. 15-pg., 2024-03-23.

Abstract

Tropical soils play a critical role in the global biogeochemical cycles and are essential for maintaining the Earth's carbon balance. Understanding the dynamics of dissolved organic matter (DOM) is paramount due to its implications for ecosystem functioning and nutrient cycling. This study comprehensively evaluated the origin, distribution, and composition of DOM and inorganic solutes in Brazilian tropical agricultural soils. Multiple analytical techniques were utilized to assess DOM from soil profiles (0-100 cm depth) across a spectrum of land uses, including a native Atlantic Forest, a degraded pasture, as well as intensive grazing, extensive grazing, and silvopastoral systems. Inorganic elements were quantified to assess the coupling between the organic and inorganic biogeochemical cycles. The dominance of C4 carbon in topsoil layers suggested substantial contributions of organic matter from grasses to the soil organic matter pool. However, with increased depth, C3 carbon inputs became more prominent, indicating the influence of forest vegetation that existed prior to the implementation of agricultural managements. DOM concentrations decreased with soil depth due to reduced carbon inputs, sorption to minerals, or oxidation. DOM composition did not show significant changes among different land use and managements. Lignin was identified as the primary contributor to oxidized DOM with increasing soil depth. The composition of DOM exhibited a shift from more aromatic and higher molecular weight compounds in topsoil layers to smaller, more aliphatic compounds in subsoil layers. Our key findings revealed that aliphatic compounds, particularly fatty acids, tend to accumulate in deeper soil layers. This phenomenon was consistent in pastures dominated by grasses but not in soils near treed vegetation. Overseeding (from C3 plants) did not significantly impact DOM compositions, emphasizing the persistence of C4 plants in these systems. The presence of inorganic elements in soil water extracts showed minimal impact on DOM dynamics, suggesting decoupled organic and inorganic biogeochemical cycles in tropical pasturelands. (AU)

• FAPESP's process: 23/02444-5 - Understanding intensified and integrated production systems: from the quantum world to low-carbon agriculture
• Grantee: Ladislau Martin Neto
• Support Opportunities: Research Program on Global Climate Change - Thematic Grants
• FAPESP's process: 21/08362-5 - Origin, molecular composition and fate of dissolved organic matter in intensive grazing and integrated livestock-forest systems
• Grantee: João Vitor dos Santos
• Support Opportunities: Scholarships abroad - Research Internship - Master's degree
• FAPESP's process: 20/04938-7 - Quantification and spectroscopic characterization of dissolved organic matter in soils under pastures and integrated production systems
• Grantee: João Vitor dos Santos
• Support Opportunities: Scholarships in Brazil - Master
• FAPESP's process: 17/20084-5 - Strategic practices for mitigating greenhouse gas emissions in grassland systems of the Brazilian Southeast
• Grantee: Paulo Henrique Mazza Rodrigues
• Support Opportunities: Research Program on Global Climate Change - Thematic Grants
• FAPESP's process: 19/18267-0 - Organic matter stabilization mechanisms in tropical soils with carbon sequestration areas: evaluation by physicochemical methods and carbon modeling
• Grantee: Lucas Raimundo Bento
• Support Opportunities: Scholarships in Brazil - Doctorate