Detrital Foundations of Microbial, Invertebrate, and Amphibian Community Structure in Upland and Riparian Forested Vernal Pools

Background/Question/Methods

Vernal pools are temporary ponds and wetlands characterized by seasonal inundation and wetting- drying cycles. These habitats are important sites for many obligate pool-breeding organisms. Forested pools are closely linked to leaf litter inputs that form the detrital basis of the food web. Leaf litter provides protected physical habitat for amphibians and invertebrates. Litter breakdown by decomposers and shredders releases nutrients for uptake by higher trophic levels, and may contribute to pool water chemistry. Our study seeks to elucidate the connections among adjacent tree community structure, decomposer community structure, pool hydrology, and pool chemistry. Twenty-one pool sampling locations within upland and riparian ecotypes in Jennings Woods (Ravenna, OH) were assessed for leaf litter biomass, tissue chemistry, and community variables.  Surface litter was collected after leaf senescence on one date in November 2010. Three replicate 25 cm² quadrats were removed at 1 m intervals along the longitudinal axis of each pool. Litter was sorted to species, and dry biomass of each component species determined. Polar compounds were extracted with methanol and nonpolar compounds with dichloromethane.  

Results/Conclusions

RDA analysis showed that ecotype explained 29.22% of detrital biomass variation (p-value=< .001).  Species including Fagus grandifolia , Acer rubrum, and Nyssa sylvatica were strongly associated with upland pools;  Acer saccharum, Quercus rubrum, and Platanus occidentalis contributed especially to riparian detritus.  Vitus riparia and Prunus serrotina were distributed independently of ecotype;  P. serrotina was the only leaf species identified at all sites. RDA analysis of percent extractives constrained by ecotype explained 15.89% of the variation in polar compounds and 11.12% for nonpolar compounds (p-values < .001).  These compounds are labile and readily available to a rapid-cycling detrital food web. The distinction in leaf chemical inputs between the two ecotypes shows that detrital sources are creating two potentially different niches in upland vs. riparian pools. Pool community structure may also follow this pattern of separation. Molecular characterization of microbial communities in pool litter and sediment will be compared to invertebrate, amphibian, and physiochemical data to determine whether ascending trophic levels are indeed shaped by niche-based factors.