Seedling survival of Mediterranean shrubland species in relation to root :shoot ratio, seed size and water and nitrogen use

1. We hypothesized that in Mediterranean plant communities seedling surviva l of different species during the drought period would be related to their ability to use below-ground resources, particularly water and nitrogen, 2. For 5 years we studied under field conditions the summer seedling surviv al of ii dominant species of a Spanish Mediterranean shrubland. We related seedling survival of the different species to their seed size and root allo cation estimated as the slope of the function root biomass vs log shoot bio mass. We used delta(13)C for the estimation of water-use efficiency and del ta(15)N and nitrogen concentration to determine the sources of nitrogen uti lized. We correlated these variables with root allocation. 3. Seedling survival of the different species was positively correlated wit h root allocation and seed size. Root allocation was also positively correl ated with seed size. delta(15)N and nitrogen concentration were also positi vely correlated with root allocation, but delta(13)C was not. 4. Under the relatively moist conditions occurring during summer 1996, high er root allocation was associated with the use of nitrogen from more nitrog en saturated microsites.