Department of Biology, Miami University 

Kaia Heitkamp*, Kati Ballo*, Jenn Butt, Melany Fisk

(*undergrad presenters)

Soils were sampled in five sites within Miami University’s Natural Areas during October 2024 (Figure 2). At each site, a 20 x 20 m deer exclosure is paired with a 20 x 20 m control plot. All honeysuckle has been removed from half of each plot (Figure 3). 

Ten 5-cm diameter soil cores were collected to a 10-cm depth from each honeysuckle or no-honeysuckle subplot in each deer exclosure and control plot. Soil subsamples were incubated in the laboratory for 19 days (Figure 4). Microbial respiration was quantified by measuring the amount of CO2 emitted during incubation, the accumulation of inorganic N was quantified as an index of net N mineralization, and the accumulation of NO3 was quantified as an index of nitrification. 

The effects of deer, honeysuckle, and their interaction were tested using a mixed effects model in R with deer and honeysuckle as fixed effects and site as a random effect.

Microbial activity and N cycle processes did not respond uniformly to the presence of deer and honeysuckle. Whereas respiratory activity was promoted by the presence of honeysuckle, especially where deer were present, net N mineralization was not sensitive to the effects of deer or honeysuckle, and the transformation of ammonium to nitrate (i.e. nitrification) was promoted by the presence of deer. 

Greater concentrations of nitrate in soils where deer were present suggests that the activities of deer increase the potential for N loss from soil in these forest ecosystems. In the non-growing season, when plants are not active in the uptake of N, nitrate becomes susceptible to leaching or undergoing denitrification processes that produce N2O and N2 gasses, contributing to aquatic nutrient enrichment and greenhouse gas production.