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

[摘要] The partitioning of photosynthates toward biomass compartments plays a crucialrole in the carbon (C) sink function of forests. Few studies have examined howcarbon is allocated toward plant compartments in drought-prone forests. Weanalyzed the fate of gross primary production (GPP) in relation to yearly water deficit in an oldevergreen Mediterranean Quercus ilex coppice severely affected bywater limitations. Carbon fluxes between the ecosystem and the atmospherewere measured with an eddy covariance flux tower running continuously since2001. Discrete measurements of litterfall, stem growth and f_APARallowed us to derive annual productions of leaves, wood, flowers and acorns,and an isometric relationship between stem and belowground biomass has beenused to estimate perennial belowground growth. By combining eddy covariancefluxes with annual net primary productions (NPP), we managed to close a C budget andderive values of autotrophic, heterotrophic respirations and carbon-useefficiency (CUE; the ratio between NPP and GPP). Average values of yearlynet ecosystem production (NEP), GPP and R_eco were 282, 1259 and 977 g C m⁻². Thecorresponding aboveground net primary production (ANPP) components were 142.5, 26.4 and 69.6 g C m⁻² forleaves, reproductive effort (flowers and fruits) and stems, respectively. NEP, GPP andR_eco were affected by annual water deficit. Partitioning to thedifferent plant compartments was also impacted by drought, with a hierarchyof responses going from the most affected – the stem growth – to the leastaffected – the leaf production. The average CUE was 0.40, which is well in therange for Mediterranean-type forest ecosystems. CUE tended to decrease less drastically in response to drought than GPP and NPP did, probably due todrought acclimation of autotrophic respiration. Overall, our results providea baseline for modeling the inter-annual variations of carbon fluxes andallocation in this widespread Mediterranean ecosystem, and they highlight the valueof maintaining continuous experimental measurements over the long term.

[学科分类] 地球化学与岩石