Responses of Quercus suber seedlings under different light and water treatments. Greenhouse and field experiments

Abstract

11 pages, 4 figures, 20 references. We thank the "Consejería de Medio Ambiente" (Andalusian Government), and Felipe Oliveros, the Director of "Los Alcornocales" Natural Park for the facilities and support to carry out our field work. We thank Ana Murillo, Juan Rubio, Francisco Conde, Miguel Ángel Calero, Loles Bejarano and Carlos Casimiro for their help in the greenhouse experiment. El libro referenciado ha sido publicado con motivo de Conference Proceedings: Conference held at the University of Huelva on 20-22 october, 2005. Organised bay: Departamento de Ciencias Agroforestales, Universidad de Huelva, Spain. Centro de Estudos Florestais, Universidade Técnica de Lisboa, Portugal. ; The objective of this study is to understand the response of Quercus suber seedlings to light and water, two limiting factors of their growth and survival in Mediterranean woody plants. Greenhouse and field experiments were conducted to contrast the results from both types of experiments. At the greenhouse experiment, Quercus suber seedlings were grown at three treatments of light (3%, 27% and 100% of incident light) and daily irrigation. When plants had four months old, half of the individuals did not receive any water, so we had then two water treatments (water and drought) within each light treatment. After two months, different variables were measured. At the field experiment, Quercus suber acorns were sown in three microhabitats with different light conditions (open, under tree and deep shade) in "Los Alcornocales" Natural Park (Cádiz). These microhabitats have similar light radiation than the treatments used at the greenhouse experiment. The greenhouse experiment results showed that the acorn mass was important for determining the seedling mass on the first stages, and that importance increased with light limitation. Thus, a greater seedling biomass was strongly associated with a bigger acorn mass under deep shade, but with increasing light levels the association between seedling and acorn mass became lower and non-significant. Quercus suber seedlings responded to light restriction with a decrease in the relative growth rate (RGR) and then the seedlings had lower biomass. This decrease in RGR was mainly caused by a decrease of the net assimilation rate (NAR). However, specific leaf area (SLA) and stem mass ratio (SMR) increased under shade as a way to enhance light capture. The response to water limitation was a general decrease of RGR, but interestingly, the effect of drought was negligible under deep shade conditions. The results of the field experiment were similar to those in the greenhouse experiment, which reinforce the conclusions of this study. Seedlings from open microhabitats (with more light) had a greater biomass than seedlings under tree or deep shade microhabitats. Also, the response to light limitation was an increase of specific leaf area (SLA), an increase in stem mass ratio and stem length. In contrast with the growth data, the survival rate of seedlings after the summer drought was greater under trees than in the open habitats. Then, it seems to exist an uncoupling between growth and survival of Quercus suber seedlings under different conditions. In this way, the best microhabitat for the growth (open microhabitat) is not the best for seedling survival, while medium shade microhabitat seems to be the best suited for Quercus suber regeneration. ; This study was supported by grants PFPU-MEC to IMPR and PFPI-MEC to JLQ (BES- 2003-1716), and by the coordinated Spanish CICYT project HETEROMED (REN2002- 04041-C02). This research is part of the REDBOME and GLOBIMED (www.globimed. net) network on forest ecology. ; Peer reviewed