Linking Belowground Biotic Components and Soil Organic Carbon Across Tropical Forest Succession

Abstract

Tropical land cover is continuously changing due to the increasing demand for agricultural products, affecting global carbon dynamics. As a consequence, there are more secondary forests than primary forests in tropical regions. Forest regrowth can increase aboveground biomass significantly influencing carbon sinks. However, we know less about what is happening belowground with soil carbon. Plant roots and fungal communities directly influence belowground carbon stocks through inputs, stabilization, and output processes. Yet, little is known about what happens to plant roots and fungal communities across tropical secondary forest succession. The goal of this research was to use a trait-based approach to study how plant roots and fungal communities change across forest succession to better understand soil carbon trends. In addition, this research aimed to understand how tropical soil diversity influence changes in belowground components. I collected 0-10cm depth soil samples from 36 sites located in Puerto Rico representing Oxisols, Mollisols and Alfisols soil orders and different forest successional stages categorized as pastures, and 15-20, 20-40, and 40-70 years old forests. I analyzed root functional traits and fungal functional groups abundance related to input, stabilization, and output of soil carbon. Root biomass was a poor predictor of changes in root dynamics across forest succession and with different soil properties. However, other functional traits differed between vegetation types (pastures vs. forests) and differed among soil orders. Root traits explained a third percent of carbon stocks in soils. Fungal functional groups differ among secondary forest succession in tropical systems but did not differ among soil orders. Arbuscular mycorrhizal fungi decreased with forest succession, while ectomycorrhizal fungi increased. Fungal functional groups explained a fourth of carbon stocks in soils. These findings suggest that root traits and fungal groups among successional stages could influence belowground processes related to carbon. Root traits and fungal groups on their own may not be good predictors of soil carbon, but incorporating soil diversity, nutrient availability, and root-fungi-soil interactions can help understand the variability in response to tropical secondary forest succession.