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 survival 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 survival of ii dominant species of a Spanish Mediterranean shrubland. We related seedling survival of the different species to their seed size and root allocation estimated as the slope of the function root biomass vs log shoot biomass. We used delta(13)C for the estimation of water-use efficiency and delta(15)N and nitrogen concentration to determine the sources of nitrogen utilized. We correlated these variables with root allocation. 3. Seedling survival of the different species was positively correlated with root allocation and seed size. Root allocation was also positively correlated with seed size. delta(15)N and nitrogen concentration were also positively correlated with root allocation, but delta(13)C was not. 4. Under the relatively moist conditions occurring during summer 1996, higher root allocation was associated with the use of nitrogen from more nitrogen saturated microsites.