Mycorrhizal community composition of Quercus oleoides as a function of stand maturity in the regenerating dry tropical forest

Background/Question/Methods

Species rich dry tropical forests (DTFs) are the most endangered ecosystems in the tropical biome. In Costa Rica, deforestation of the DTF has occurred for centuries; however, conservation efforts over the past 30 years have restored these forests to 47.9% of their original extent. To understand the role of mycorrhizal fungi in the regeneration of DTFs, this project studies mycorrhizal communities associated with younger and older stands of Quercus oleoides (tropical live oak) in the Área de Conservación Guanacaste (ACG), where Q. oleoides were once regionally dominant. This project evaluates age related ectomycorrhizal (EM) diversity between oak stands and how the balance between arbuscular mycorrhizal (AM) and EM abundance reflects stand age.

Data collection occurred over two weeks in July 2011. Using two 20-m x 50-m plots from young and old stands, soil cores were collected and the associated ectomycorrhizal root tips were pooled for analysis of species composition using molecular methods. Sporocarps were collected for DNA analysis of fresh fungal tissue. DNA sequences were used to identify ectomycorrhizal fungi using BLAST searches against GenBank and UNITE databases. Oak roots without mantles were analyzed for arbuscular mycorrhizal (AM) presence by staining with Trypan blue.

Results/Conclusions

Results suggest that: 1) EM diversity is greater in older stands of oak; 2) older stands contain more rare EM species than younger stands, such that overlap in community composition between stand age is small; and 3) the balance between AM fungi and EM abundance reflects stand age- greater AM root colonization in younger stands and EM dominance in older stands.

The DTF is a region which has been understudied and where little is known of mycorrhizal diversity, community turnover and function. The importance of studying community structure in these forests is essential to strengthening conservation efforts, supporting succession, preserving biodiversity on numerous trophic levels, and improving our resources for carbon sequestration. This investigation will provide baseline data for future mycorrhizal studies and serve as a complement to the aboveground studies in this region.