OOS 10-8
Unearthing patterns of below ground tropical tree fine root diversity and abundance through DNA metabarcoding
Metagenomic and ecological forensic approaches represent one promising way that ecologists can apply the tools of genomics to investigate heretofore hidden ecological processes critical to understanding the structure and function of diverse plant communities. We used massively parallel sequencing and a DNA barcode reference library to explore below ground patterns of species distribution and abundance across a mapped tropical forest plot on Barro Colorado Island (BCI), Panama. The method allows us to determine the species identity of fine roots in mixed species samples and, surprisingly, provides a semi-quantitative estimate of below ground species relative abundances. Specifically, we ask 1) What is the species diversity present within single soil volumes? 2) How much species similarity do we see between a soil core and the above ground neighborhood and what does this tell us about the spatial scale over which trees interact below ground? and 3) What is the relationship between above ground relative abundance (as determined by total basal area of a given species in the neighborhood) and below ground abundance (as determined by sequence abundance of a species within a soil volume) and which species function traits predict below ground fine root abundance?
Results/Conclusions
We sampled 625 soil cores across the plot and recovered sufficient data from 550 of these for the below analyses. Our soil cores sampled < 5 m2 of the BCI plot and we detected fine roots of up to 50% of those tree and liana species present in 50 ha, a result that implies spatially extensive and complex below ground plant neighborhoods relative to above ground neighborhoods. Fine root species richness within our 10 cm3 soil cores averaged 8.3 (SD = 3.9). Local above ground plant neighborhoods are often poor predictors of below ground species composition at a given point with community similarity indices comparing above and below ground neighborhoods averaging 15%. Root networks overlap to a greater extent below ground than do leaf canopies, with an average of 2 – 3 times the number of species in the same core than have canopies overlapping a sample point. We find that that a species’ below ground fine root abundance is strongly positively correlated with species’ above ground basal area, maximum height (e.g. growth form), and shows weaker, but still significant, correlation with above ground leaf and stem functional traits, including wood density.