Key message

Seedling survival inPinus pineais controlled by both water status and photosynthetic performance. Optimal regeneration niche for the species is found at mid-shaded sites.

Abstract

Summer survival has been identified as the main bottleneck preventing natural regeneration in Mediterranean forests, although the physiological processes resulting in seedling mortality are not sufficiently known. In the present work, the effect of water status and photosynthetic performance on seedling survival and regeneration niche in a Mediterranean pine (Pinus pinea L.) was analyzed by means of a modeling approach. Midday water potential was modeled as a nonlinear function of environmental factors, and this model was coupled with an existing model for carbon assimilation. A model for seedling survival was then constructed using lifetime analysis techniques, including predicted values of daily and cumulative net assimilation and probability for critical midday water potentials as predictors. The model was applied over a wide range of irradiance environments in order to identify the optimal regeneration niche for the species. Results indicate that midday water potential for P. Pinea seedlings is affected by relative soil water content, leaf temperature, and irradiance, with younger seedlings being more likely to reach critical values. Seedling survival in P. pinea is controlled by both water status and photosynthetic performance, with mortality being triggered by the joint occurrence of low water potentials and negative assimilation rates, although photoassimilates stored during the spring season increase survival in older seedlings. Simulations indicated that seedling survival is optimized in shaded environments, while carbon assimilation reaches maximum values on more open sites, thus the optimal regeneration niche for the species is found on mid-shaded locations.