Spatial and temporal variations of soil respiration in a Eucalyptus plantation in Congo

https://doi.org/10.1016/j.foreco.2004.07.019Get rights and content

Abstract

Our objectives were to quantify soil respiration in a 3-year-old Eucalyptus plantation in coastal Congo and to investigate both temporal and spatial variations of this major component of ecosystem respiration. Soil respiration exhibited pronounced seasonal variations that clearly reflected those of soil water content, with minimum values below 1.6 μmol m−2 s−1 at the end of the dry season in September and a maximum value of 5.6 μmol m−2 s−1 after re-wetting in December. An empirical model describing the relationship between soil respiration and soil water content predicts the seasonal variations in soil respiration reasonably well (R2 = 0.88), even if the effects of soil temperature and soil water content may be confounded since both factors co-vary across seasons. Spatial heterogeneity of soil respiration was clearly affected by management practices with higher respiration rate in slash inter-rows which received higher amounts of detritus at the logging stage, and lower respiration rate in haulage inter-rows used for heavy vehicle traffic. Higher values of soil respiration were also recorded in the vicinity of trunks than in the middle of the inter-rows. While soil water content is the main determinant of seasonal variation of soil respiration, it poorly accounts for its spatial variability over the experimental stand, except for days with low soil water content. Soil respiration was related neither to root biomass nor to soil carbon content, but was positively correlated with both leaf and total aboveground litter (i.e. leaf, bark and woody debris). Plots exhibiting the highest soil respiration also contained the highest amounts of aboveground litter. Microbial respiration associated with litter decomposition is likely a major component of soil respiration, and the spatial heterogeneity in litter fall probably accounts for most of its spatial variability in this Eucalyptus plantation.

Introduction

The evaluation of biospheric fluxes and stocks of carbon is of major importance in the context of increasing CO2 concentration in the atmosphere and the related potential change in climate. Carbon sequestration in forested ecosystems often results from a small difference between photosynthetic carbon fixation (gross primary production) and ecosystem respiration (Granier et al., 2000, Valentini et al., 2000). Soil is the biggest carbon pool of the continental biosphere (Schimel, 1995) and requires a particular attention, especially for short rotation plantation because it is a major compartment for durable carbon sequestration, the aboveground biomass being frequently removed and transformed into wood products with short life-times. While conversion of forest to pasture (Fearnside and Barbosa, 1998) or forest to tree plantation (Smith et al., 2002) often led to a net loss of soil carbon, more variable results have been collected for afforestation depending on previous land used, climate, soil type and planted species (Paul et al., 2002). For example, growing an Eucalyptus plantation (E. camaldulensis) over tropical savanna on sandy Entisol in Brazil led to a 17% decrease in soil organic carbon after one cycle whereas there was a slight increase observed on loamy Oxysol (Zinn et al., 2002). The soil texture and the ability of clay minerals to protect organic matter from microbial mineralisation are thought to affect carbon dynamics in afforested areas (Paul et al., 2002).

Soil respiration is one of the main components of ecosystem respiration (Granier et al., 2000, Janssens et al., 2001), and small changes in soil respiration may strongly affect soil carbon sequestration (Raich and Schlesinger, 1992). Therefore, it is important to obtain good estimates of soil respiration and to understand environmental controls on the underlying processes. Soil respiration is the sum of an autotrophic component by roots and the associated rhizosphere and a heterotrophic component by soil micro-organisms that decompose the organic materials from both aboveground and belowground litter (Bowden et al., 1993, Boone et al., 1998, Epron et al., 1999b, Epron et al., 2001). Several factors may affect these two processes. Soil respiration exhibits a high spatial and temporal variability. Spatial heterogeneity of soil respiration has been related to either root biomass, microbial biomass, litter amount, soil organic carbon, soil nitrogen, cation exchange capacity, soil bulk density, soil porosity, soil pH, or site topography (Hanson et al., 1993, Fang et al., 1998, La Scala et al., 2000, Xu and Qi, 2001). Seasonal variations of soil respiration have often been associated with either changes in soil temperature (Anderson, 1973, Edwards, 1975, Ewel et al., 1987a; Fang et al., 1998, Longdoz et al., 2000) or changes in both soil temperature and soil water content (Garret and Cox, 1973, Hanson et al., 1993, Davidson et al., 1998, Epron et al., 1999a; Qi and Xu, 2001, Xu and Qi, 2001).

Up to now, only few studies have dealt with soil respiration in tropical plantations (Ewel et al., 1987a, Ewel et al., 1987b; Lamade et al., 1996, Fang et al., 1998) despite their relevance to the “Clean Development Mechanism”. Eucalyptus plantations account for 25% of tropical plantations and cover about 1.5 × 105 km2. In the past 25 years, 430 km2 of clonal Eucalyptus plantations have been established in the littoral savannas of Congo and intensively managed for pulpwood production. The present study was done in the framework of an integrated program on carbon fluxes and sequestration in perennial tropical plantations (ATP CIRAD). Specifically, our objective was first to quantify the annual soil carbon efflux in a 3-year-old Eucalyptus plantation in coastal Congo. We investigated the effects of seasonal changes in soil temperature and soil water content on soil respiration. We further analysed the spatial variation of soil respiration within the stand and we attempted to relate these variations to the plantation structure and to local soil characteristics.

Section snippets

Site description

The study site is located in the Eucalyptus plantation zone, which covers about 430 km2 along the Atlantic coast in the Pointe Noire region (Congo, 4° S, 12° E, 100 m elevation). The mean annual air humidity and air temperature are high (85% and 25 °C) with low seasonal variations (about 2% and 5 °C, respectively). Mean annual precipitation is 1200 mm with a dry season between May and September. The soil is an arenosol according to the F.A.O. classification. The pH of the topsoil (0–20 cm) is about

Temporal trend in soil respiration

Soil respiration exhibited pronounced seasonal variations with minimum values below 1.6 μmol m−2 s−1 at end of the dry season in September and a maximum value of 5.6 μmol m−2 s−1 after re-wetting in December (Fig. 1). This pattern clearly reflected those of soil water content, which decreased from 10.8% in January to 3.1% in September. Soil temperature decreased from March (30 °C around day 70) to September (25 °C around day 260). There was a rather poor correlation between soil respiration and soil

Discussion

Seasonal variation in soil respiration is thought to be largely explained by either soil temperature alone (Anderson, 1973, Edwards, 1975, Longdoz et al., 2000) or soil temperature and water content in sites exhibiting a dry season as in some temperate areas or under Mediterranean climate (Garret and Cox, 1973, Hanson et al., 1993, Keith et al., 1997, Davidson et al., 1998, Epron et al., 1999a; Qi and Xu, 2001, Rey et al., 2002). Soil temperature exerted a strong influence on soil respiration

Acknowledgements

This research activity was carried out in the framework of the CIRAD funded ‘ATP Carbon’ project. UR2PI and ECO-SA (Eucalyptus Du Congo, SA) have provided additional funding and research facilities.

References (51)

  • R.D. Bowden et al.

    Contributions of aboveground litter, belowground litter, and root respiration to total soil respiration in a temperate mixed hardwood forest

    Can. J. For. Res.

    (1993)
  • D. Brown et al.

    Models in Biology: Mathematics, Statistics and Computing

    (1994)
  • K. Butterbach-Bahl et al.

    Effect of tree distance on N2O and CH4-fluxes from soils in temperate forest ecosystems

    Plant Soil

    (2002)
  • E.A. Davidson et al.

    Soil water content and temperature as independent or confounded factors controlling soil respiration in a temperate mixed hardwood forest

    Global Change Biol.

    (1998)
  • E.A. Davidson et al.

    Effects of soil water content on soil respiration in forests and cattle pastures of eastern Amazonia

    Biogeochemistry

    (2000)
  • N.T. Edwards

    Effects of temperature and moisture on carbon dioxide evolution in a mixed deciduous forest floor

    Soil Sci. Soc. Am. J.

    (1975)
  • D. Epron et al.

    Soil CO2 efflux in a beech forest: dependence on soil temperature and soil water content

    Ann. For. Sci.

    (1999)
  • D. Epron et al.

    Soil CO2 efflux in a beech forest: the contribution of root respiration

    Ann. For. Sci.

    (1999)
  • D. Epron et al.

    Seasonal dynamics of soil carbon dioxide efflux and simulated rhizosphere respiration in a beech forest

    Tree Physiol.

    (2001)
  • K.C. Ewel et al.

    Soil CO2 evolution in Florida slash pine plantations. I. Changes through time

    Can. J. For. Res.

    (1987)
  • K.C. Ewel et al.

    Soil CO2 evolution in Florida slash pine plantations. II. Importance of root respiration

    Can. J. For. Res.

    (1987)
  • C. Fang et al.

    Soil CO2 efflux and its spatial variation in a Florida slash pine plantation

    Plant Soil

    (1998)
  • G. Fystro

    The prediction of C and N content and their potential mineralisation in heterogeneous soil sample using Vis–NIR spectroscopy and comparative methods

    Plant Soil

    (2002)
  • H.E. Garret et al.

    Carbon dioxide evolution from the floor of an oak-hickory forest

    Soil Sci. Soc. Am. Proc.

    (1973)
  • R. Gasche et al.

    Spatial variability of NO and NO2 flux rates from soil of spruce and beech forest ecosystems

    Plant Soil

    (2002)
  • Cited by (0)

    View full text