Linking water and carbon fluxes in a Mediterranean oak woodland using a combined flux and δ18O partitioning approach
2 Instituo Superior de Agronomia, Universidade Tecnica de Lisboa
3 UFZ Leipzig
4 Agroecosystem research
P 3.2 in Research Yields: Ideas Pursued to the End
Water is one of the key factors driving ecosystem productivity, especially in water-limited
ecosystems, where global climate change is expected to intensify drought and alter precipitation patterns.
One such ecosystem is the ‘Montado’, where two vegetation layers respond differently to drought: oak trees
avoid drought due to their access to deeper soil layers and ground water while herbaceous plants, surviving
the summer in the form of seeds. We aimed at 1) quantifying the impact of the understory herbaceous
vegetation on ecosystem carbon and water fluxes throughout the year, 2) determining the driving
environmental factors for evapotranspiration (ET) and net ecosystem exchange (NEE) and 3) disentangling
how ET components of the ecosystem relate to carbon dioxide exchange.
We present one year data set comparing modeled and measured stable oxygen isotope signatures (δ18O) of
soil evaporation, confirming that the Craig and Gordon equation leads to good agreement with measured
δ18O of evaporation (Dubbert et al. 2013).
Partitioning ecosystem ET and NEE into its three sources revealed a strong contribution of soil evaporation
(E) and herbaceous transpiration (T) to ecosystem ET during spring and fall. In contrast, soil respiration (R)
and herbaceous net carbon gain contributed to a lesser amount to ecosystem NEE during spring and fall,
leading to consistently smaller water use efficiencies (WUE) of the herbaceous understory compared to the
cork-oaks. Here, we demonstrate that the ability to assess ET, NEE and WUE independent of soil evaporation
dynamics enables the understanding of the mechanisms of the coupling between water and carbon fluxes and
their responses to drought.