Abstract
Environmental heterogeneity mostly dominated by differing light regimes affects the expression of phenotypic plasticity, which is important for plant growth and survival, especially in the forest understory. The knowledge about these responses to this heterogeneity is a key factor for forest restoration initiatives. In this study, we determine several phenotypic responses to contrasting light conditions in five native tree seedling species of La Cangreja National Park, Central Pacific of Costa Rica, four of them with threatened or relict populations. After 14 weeks at a medium gap condition (24% of full sun), seedlings were transferred and acclimated for 11 weeks to three different natural light regimes: large gap (LG), medium gap (MG) and small gap (SG), corresponding to 52%, 24%, 9% of the mean direct and indirect radiation at each site from full sun. Growth, biomass allocation and leaf gas exchange were measured after the acclimation period. Four species strongly reduced relative growth rate (RGR) in the lower light condition. Total biomass (TB) and RGR were different in Hymenaea courbaril and Platymiscium curiense. H. courbaril and Astronium graveolens had significant changes in the maximum assimilation rate, with a mean value in the LG of 11.02 and 7.70 micromolCO2/m2s, respectively. P. curuense showed the same trend and significant changes in RGR and biomass allocation. Aspidosperma myristicifolium and Plinia puriscalensis showed no adjustments to the light regimes in any of the measured variables. This study remarks the importance of determining the growth and physiological performance of these tree native species. It also demonstrates that the most threatened species are those with the less plastic responses to the light regimes, which stresses the difficult situation of their natural populations. This study highlights an urgent definition of the conservation and restoration needs of the degraded forests of the Costa Rican Central Pacific area, where these species dwell.
Highlights
Tropical forests present great variability in light regimes (Chazdon & Fetcher 1984, Chazdon & Pearcy 1991), which have influenced the growth and development patterns of many seedlings (Théry 2001), which has been considered a potentially important mechanism to promote local plant biodiversity (Kitajima & Pooter 2008)
The Large gap (LG) condition received 25 and 40% more of the ISF and direct site factor (DSF) than the medium gap (MG) and small gap (SG) conditions, respectively. These results show that the sites used for the light treatment acclimation were significantly contrasting between them, and represent a diversity of light regimes naturally found in the present conditions of the forested areas of the Central Pacific zone
Growth and biomass allocation: The four species presented a gradient of mean SLA in the following order: P. curuense, A. graveolens, H. courbaril and A. myristicifolium
Summary
Tropical forests present great variability in light regimes (Chazdon & Fetcher 1984, Chazdon & Pearcy 1991), which have influenced the growth and development patterns of many seedlings (Théry 2001), which has been considered a potentially important mechanism to promote local plant biodiversity (Kitajima & Pooter 2008). Plants have developed a series of morphological and physiological adaptations to cope with environmental light heterogeneity Changes in these traits may possess a diversity of plastic phenotypic responses in each species (Valladares et al 2007, Lambers et al 2008), enabling them to survive in different environments according to their light requirements. This study aims to characterize the growth, biomass allocation and carbon assimilation of seedlings of five tree species native to the Central Pacific area of Costa Rica. This region is dominated by wet forests with a significant dry season which has been severely degraded since last century.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
