Responses of Quercus Suber Seedlings under Different Light and Water Treatments. Greenhouse and Field Experiments

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 planted 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 mass was strongly associated with a bigger acorn mass under deep shade, but with increasing levels of light 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 …