Linking carbon and water cycles in forests: from the cell to the ecosystem level

Dendrochronology combined with stable carbon (C) isotopes has given us the opportunity to travel back in time, from decades to centuries and even millennia and reconstruct tree growth and water-use efficiency in response to major changes that forests have been facing. A crucial aspect, which has been poorly investigated so far, is to understand how well the forest canopy phenology and physiology, namely C uptake and water lost through transpiration, are “synchronized” with the secondary C investment in tree stem during tree ring formation. In this respect, xylogenesis allows us to take a closer look at the annual ring, zoom into a single cell and explore the dynamics of tree growth and C allocation at fine time scale. We will present results from a unique study linking the canopy phenology and C uptake to the development of xylem cells during tree-ring formation. The study was conducted on a mixed forest in New Hampshire (U.S.A.), dominated by Quercus rubra L.; Acer rubrum L. and Pinus strobus L. The site is equipped with an eddy-covariance tower and a phenocam to continuously monitor meteorological parameters together with C and water fluxes (i.e.; Gross Primary Productivity and evapotranspiration) and canopy phenology. Microcores were sampled weekly from March until November 2015 from 5 trees per species. Differences among species in term of dynamic of tree growth will be discussed in relation to the plant functional type and wood anatomical (i.e.; diffuse vs. ring porous wood) and hydraulic (i.e.; isohydric vs. anisohydric) features. Furthermore, we will explore how the different phenological stages of cambial activity are affected by climate and coupled with changes in canopy phenology and physiology.