Articles | Volume 11, issue 23
Biogeosciences, 11, 6855–6869, 2014

Special issue: Climate extremes and biogeochemical cycles in the terrestrial...

Biogeosciences, 11, 6855–6869, 2014

Research article 09 Dec 2014

Research article | 09 Dec 2014

How drought severity constrains gross primary production(GPP) and its partitioning among carbon pools in a Quercus ilex coppice?

S. Rambal1,5, M. Lempereur1,6, J. M. Limousin2, N. K. Martin-StPaul1,3,7, J. M. Ourcival1, and J. Rodríguez-Calcerrada4 S. Rambal et al.
  • 1Centre d'Ecologie Fonctionnelle et Evolutive CEFE, UMR5175, CNRS, Université de Montpellier, Université Paul-Valéry Montpellier, EPHE 1919 Route de Mende, 34293 Montpellier, Cedex 5, France
  • 2Department of Biology, University of New Mexico, MSC03 2020, Albuquerque, New Mexico 87131-0001, USA
  • 3Laboratoire Ecologie Systématique et Evolution CNRS, Orsay, 91405, France
  • 4Grupo de Investigación en Genética y Fisiología Forestal, E.T.S.I. Montes, Universidad Politécnica de Madrid, Ciudad Universitaria S/N., 28040 Madrid, Spain
  • 5Universidade Federal de Lavras, Departamento de Biologia, CP 3037, CEP 37200-000, Lavras, MG, Brazil
  • 6Agence de l'Environnement et de la Maîtrise de l'Energie 20, avenue du Grésillé, BP 90406, 49004 Angers, Cedex 01, France
  • 7INRA, URFM, Ecologie des Forêts Méditerranéennes, UR629, Domaine Saint Paul, Site Agroparc, 84914 Avignon, Cedex 9, France

Abstract. The partitioning of photosynthates toward biomass compartments plays a crucial role in the carbon (C) sink function of forests. Few studies have examined how carbon is allocated toward plant compartments in drought-prone forests. We analyzed the fate of gross primary production (GPP) in relation to yearly water deficit in an old evergreen Mediterranean Quercus ilex coppice severely affected by water limitations. Carbon fluxes between the ecosystem and the atmosphere were measured with an eddy covariance flux tower running continuously since 2001. Discrete measurements of litterfall, stem growth and fAPAR allowed us to derive annual productions of leaves, wood, flowers and acorns, and an isometric relationship between stem and belowground biomass has been used to estimate perennial belowground growth. By combining eddy covariance fluxes with annual net primary productions (NPP), we managed to close a C budget and derive values of autotrophic, heterotrophic respirations and carbon-use efficiency (CUE; the ratio between NPP and GPP). Average values of yearly net ecosystem production (NEP), GPP and Reco were 282, 1259 and 977 g C m−2. The corresponding aboveground net primary production (ANPP) components were 142.5, 26.4 and 69.6 g C m−2 for leaves, reproductive effort (flowers and fruits) and stems, respectively. NEP, GPP and Reco were affected by annual water deficit. Partitioning to the different plant compartments was also impacted by drought, with a hierarchy of responses going from the most affected – the stem growth – to the least affected – the leaf production. The average CUE was 0.40, which is well in the range for Mediterranean-type forest ecosystems. CUE tended to decrease less drastically in response to drought than GPP and NPP did, probably due to drought acclimation of autotrophic respiration. Overall, our results provide a baseline for modeling the inter-annual variations of carbon fluxes and allocation in this widespread Mediterranean ecosystem, and they highlight the value of maintaining continuous experimental measurements over the long term.

Short summary
The partitioning of carbon input in biomass has a key role in the sink function of forests. We analyzed how carbon is allocated in relation to drought in an evergreen Mediterranean forest. Carbon exchanges were drastically affected by drought. Partitioning was impacted with a hierarchy of responses going from the most affected, the stem, to the least one, the leaves. 40% of carbon input is allocated in biomass and this proportion tended to decrease with drought due to acclimation of respiration.
Final-revised paper