Modeling CO2 production and transport in a deep Ferralsol under eucalypt plantations subjected to contrasted rainfall regimes

Abstract

Tropical forests strongly influence the concentrations of carbon dioxide (CO2) in the atmosphere. Silvicultural practices in planted forests influence the fluxes of this greenhouse gas and the major factors driving greenhouse gas production in forest soils (root density, substrate supply, temperature, water content, microbial community, &) change with soil depth. As previously described in the work plan of the PhD grant (FAPESP 2015/24911-8), our study aims to assess the consequences of drought on the temporal variability of CO2 production throughout very deep soil profiles in Eucalyptus grandis plantations, before the harvest then in coppice, the first 1.5 year after clear-cutting. To process the measurements of gas concentrations at different depths in the soil carried out during the PhD, a mechanistic modeling approach must be used. This project aims at assessing the production of gas throughout very deep soil profiles and to infer the sensibility of gas production to environmental factors. For these purposes, we will adapt to Eucalyptus and use the new numerical model Min3P. We shall first focus on the modeling of water uptake and dynamics in soil and rhizosphere depending on throughfall exclusion. The second step will focus on the inclusion of CO2 emission from root decomposition and root respiration, and then compare climatic series representing future climatic scenarios on CO2 production in tropical eucalypt plantations growing on deep Ferralsols soils. Modeling greenhouse gas emissions from soils is important to: i) quantify carbon source/sink fluxes as part of the global carbon budget, ii) improve the current biogeochemical models predicting the effect of drought periods on CO2 effluxes, and iii) identify more sustainable silvicultural practices for tropical planted forests in a context of climate change. (AU)