Soil C dynamics after deforestation and subsequent conversion of arable cropland to grassland in humid temperate areas

Agustín Merino; Beatriz Omil; Verónica Piñeiro; Nieve Barros; Pablo Souza-Alonso; Julio Campo

doi:10.1016/j.scitotenv.2023.165793

Soil C dynamics after deforestation and subsequent conversion of arable cropland to grassland in humid temperate areas

Sci Total Environ. 2023 Nov 25:901:165793. doi: 10.1016/j.scitotenv.2023.165793. Epub 2023 Jul 24.

Authors

Agustín Merino¹, Beatriz Omil¹, Verónica Piñeiro², Nieve Barros², Pablo Souza-Alonso³, Julio Campo²

Affiliations

¹ Department of Applied Physics, University of Santiago de Compostela, 27002 Lugo, Spain; Elemental Analysis RIAIDT, University of Santiago de Compostela, 27002 Lugo, Spain; Institute of Ecology, National Autonomous University of Mexico, Mexico City 04510, Mexico; Soil Science and Chemistry Department, University of Santiago de Compostela, 27002 Lugo, Spain.
² Department of Applied Physics, University of Santiago de Compostela, 27002 Lugo, Spain; Elemental Analysis RIAIDT, University of Santiago de Compostela, 27002 Lugo, Spain; Institute of Ecology, National Autonomous University of Mexico, Mexico City 04510, Mexico.
³ Department of Applied Physics, University of Santiago de Compostela, 27002 Lugo, Spain; Elemental Analysis RIAIDT, University of Santiago de Compostela, 27002 Lugo, Spain; Institute of Ecology, National Autonomous University of Mexico, Mexico City 04510, Mexico; Soil Science and Chemistry Department, University of Santiago de Compostela, 27002 Lugo, Spain. Electronic address: pablo.souza@usc.es.

PMID: 37495129
DOI: 10.1016/j.scitotenv.2023.165793

Abstract

Land use and plant-soil management influence soil organic C stocks and soil properties. This study aimed to identify the main mechanisms by which these factors alter soil organic matter (SOM) dynamics and stocks. Changes in the organic C pools and biochemical quality in different OM compartments were assessed: a) after deforestation and intensive cultivation (SOM loss) and then, b) after the conversion of cropland to grassland (SOM replenishment) in a chronosequence of recovery (1-45 years). Topsoil samples were subjected to physical fractionation to assess the distribution of free particulate OM (POM) and mineral associated OM (MAOM). SOM quality was characterized by ¹³C NMR spectroscopy, thermal analysis (DSC/TG), and microbial activity was monitored by isothermal microcalorimetry. Deforestation and intensive cultivation led to the loss of 80 % of the C stored in the upper mineral soil (up to 30-35 cm). The POM was almost depleted, MAOM underwent significant losses (>40 %) and all OM compounds, including the aromatic C, were affected. The large and unexpected loss of MAOM can be attributed to the low specific surface soil area and also to the labile (biodegradable) nature of the OM in this fraction. After 45 years, conversion of cropland to grassland recovered 68 % of the C lost in the mineral soil (mainly as MAOM), at an annual rate of 1.25 Mg C ha^-1. The present findings showed that the persistence of long-term OM depends on how strongly organic compounds are adsorbed onto mineral surfaces (i.e., the specific surface area) and the biochemical nature of OM compounds. Adequate plant-soil management favoured the replenishment of the MAOM under these experimental conditions, and this fraction was an active pool in terms of C storage and biochemical quality. This study served to test current theories about changes in soil C fractions due to land use changes and soil-plant management.

Keywords: C sequestration; Plant-soil management; SOM biochemical quality; SOM physical protection; Soil restoration; Solid-state (13)C NMR.