Fast growth involves high dependence on stored resources for shoot growth in Mediterranean evergreen trees

Abstract

Background and Aims The carbon (C) and nitrogen (N) needed for plant growth can come either from soil Nand current photosynthesis or through remobilization of stored resources. The contribution of remobilization to neworgan growth on a whole-plant basis is quite well known in deciduous woody plants and evergreen conifers, but thisinformation is very limited in broadleaf evergreen trees. This study compares the contribution of remobilized C andN to the construction of new organs in spring, and assesses the importance of different organs as C and N sources in1-year-old potted seedlings of four ecologically distinct evergreen Mediterranean trees, namely Quercus ilex, Q.coccifera, Olea europaea and Pinus hapelensis. Methods Dual 13C and 15N isotope labelling was used to unravel the contribution of currently taken up and storedC and N to new growth. Stored C was labelled under simulated winter conditions. Soil N was labelled with the fertilizationduring the spring growth. Key results Oaks allocated most C assimilated under simulated winter conditions to coarse roots, while O. europaeaand P. halepensis allocated it to the leaves. Remobilization was the main N source (>74 %) for new fine-rootgrowth in early spring, but by mid-spring soil supplied most of the N required for new growth (>64 %). Currentphotosynthesis supplied >60 % of the C in new fine roots by mid-spring in most species. Across species, the proportionof remobilized C and N in new shoots increased with the relative growth rate