THE EFFECT OF HEMLOCK WOOLLY ADELGID INFESTATION ON THE BIOGEOCHEMISTRY AND MICROBIAL COMMUNITY OF EASTERN HEMLOCK FOREST SOILS

Hemlock woolly adelgid (HWA) is an invasive insect rapidly spreading since the 1950s and killing hemlock forests throughout the Eastern United States. The effects of the HWA infestation on soil geochemistry, soil microbial and fungal community structures are not well studied and poorly understood. Mine Kill State Park (MK), in Blenheim, New York, was infested with HWA in 2011. In this study, three sampling sites were established within MK, an HWA infected site (HWA), an HWA uninfected site (NHWA), and an HWA infected and treated site (HWAT). The HWAT site was treated with insecticides. Soil chemical characteristics, microbial and fungal community structures were investigated and compared at the three sites at MK to evaluate the effect of HWA on soil ecosystems.

Three replicated soil cores were collected at each site and analyzed at three depth increments. Extractable cation and anion concentrations of the soils were determined using standard techniques. Soil temperature, moisture, pH and total organic matter content were also quantified. Illumina MiSeq next generation high-throughput sequencing was used to classify the microbial community present. Distribution of fungi was determined by phospholipid fatty acid analysis of the soil samples. These methods allowed the determination of both qualitative and quantitative differences between sites. Data analyses were completed using QIIME and Rstudio softwares.

The results indicate a qualitative and quantitative difference between infected and uninfected sites for all parameters analyzed. DNA concentrations decrease by depth at all sites with the highest values found at NHWA (5-30 ug/ g of soil). Species diversity is highest at shallow depths of the HWA site. As the pH of the HWA site increased, the abundance of Acidobacteria decreased. Generally, HWA and HWAT sites have higher concentrations of extractable ions than the NHWA site. Highest concentrations of extractable cations and anions are found in the top soil layers and decrease rapidly by depth at each site.

Declining productivity of hemlock trees has caused a shift in microbial community structure that has resulted in changes of the soil chemistry. This study provides insights to the understanding of the soil biogeochemistry response to a major ecological change in hemlock forests of New York State.