Microbial community and soil carbon dynamics vary with season and forest age along a tropical successional chronosequence

Background/Question/Methods

Tropical forest soils are important stores of carbon, holding 40% of the total tropical soil C pool. With tropical regions currently experiencing the greatest rates of deforestation and land conversion globally, many tropical research and international aid projects are focused on the fate of soil C with land use change. Soil microorganisms regulate fundamental biochemical processes in plant litter decomposition and soil organic matter (SOM) transformations. In order to predict how disturbance affects belowground C storage, it is important to understand how the belowground microbial community responds to changes in land use and land cover, and the consequences on SOM formation and stabilization. We are measuring microbial functional diversity and activity across a long-term successional chronosequence of secondary forests regrowing on abandoned pastures in the wet subtropical forest life zone of Puerto Rico. Here we report data on soil and litter microbial community composition (via phospholipid fatty acid analysis, PLFA) and microbial activity (via extracellular enzyme activity).

Results/Conclusions

Microbial community composition and extracellular enzyme activity differed by season along the wet tropical forest successional chronosequence. Despite seasonal differences, there was a persistent strong effect of land cover type and forest successional stage, or age, on overall microbial community PLFA structure. Using principal component analysis, we found differentiation in microbial community structure between active pastures, early successional, and late successional forests. Biomarkers for gram-positive and actinobacteria (i15:0 and 16:0 10Me) were associated with early successional sites (20, 30 & 40 year old secondary forests) in the dry season. These younger forest communities were identified by the biomarker for anaerobic gram-negative bacteria (c19:0) in the wet season, suggesting a strong effect of soil moisture on microbial activity, as PLFA is a measure of the active microbial biomass. The biomarker for mycorrhizal fungi (16:1ω5c) was associated with later successional forests (70 and 90 year old secondary forests) and primary forests. The separation of soil microbes into early and late successional communities parallels the clustering of aboveground tree composition data. Similar patterns in both the arboreal and the microbial community structures which differentiate the early and late successional forests and primary forests provides insight into close relationships between above and belowground dynamics. Linking soil microbial community composition with their ecological function, and understanding their response to ecosystem recovery is important for sustaining ecosystem productivity and for predicting the impact of future disturbances.