Plant roots and microbial communities may control soil carbon stocks across tropical forest secondary succession.

Abstract:

Tropical land cover is continuously changing due to the increasing demand for agricultural products, affecting global carbon dynamics. Forest regrowth in former agricultural lands can increase aboveground carbon sinks, while belowground carbon has no predictable trend. Plant roots and microbial communities directly influence belowground carbon stocks through inputs, stabilization, and output processes. However, little is known about how secondary forest succession influences roots and microbial communities, especially among a diversity of tropical soil orders. This research aimed to use a trait-based approach to study how plant roots and microbial communities change across tropical secondary forest succession on two different soil orders, and how these changes may influence soil carbon stocks. We analyzed root functional traits and microbial functional groups related to soil carbon processes in surface soils (0-10 cm depth) from 25 sites in Puerto Rico representing Mollisols and Alfisols and different forest successional stages categorized as active pastures, and young and medium-age secondary forests. Root biomass was a poor predictor of changes across forest succession and with different soil orders. However, other root traits differed between vegetation types and varied among soil orders. Fungal functional groups differ among secondary forest succession stages but did not differ among soil orders. Arbuscular mycorrhizal fungi decreased with forest succession, while ectomycorrhizal fungi increased. We did a stepwise regression and found that root traits explained a just 27%, and fungal functional groups explained 25% of carbon stocks variability in soils. These findings suggest that root traits and fungal groups change across forest succession, and it could affect soil biogeochemical cycles. Root traits and fungal groups on their own are not good predictors of soil carbon, but incorporating nutrient availability, and root-microbe-soil interactions may help understand soil carbon variability response to tropical secondary forest succession.