| Plants produce numerous chemical defense compounds in response to herbivory. Induced chemical defenses potentially influence soil dynamics by changing the nutrient ratio of the leaves, which are seasonally shed and contribute to the soil, or by affecting the detritus community through leaching of chemicals in the root zone. Manual clipping was utilized in this study to induce chemical compounds with the goal of examining the secondary effects of induced plant defenses. I removed 25% of the mass of fifteen plants of three different plant species in the Albany Pine Bush annually for two consecutive years. I then compared the soil invertebrate communities, leaf chemistry, whole plant growth and ensuing herbivory rates of damaged and undamaged Salix humilis, Quercus prinoides, and Q. iliciofolia shrub species. Nitrogen and Carbon contents of fallen leaf samples were analyzed periodically after treatment. A Berlese funnel extraction method was used to identify invertebrates from soil samples taken within 120 mm of the main plant stem for twenty plants from each species, ten of each treatment group. Soil pH was determined for all soil samples taken. Soil invertebrate communities varied significantly between treatment groups, and were not correlated with soil pH or closest plant species. These findings support the claim that soil communities are influenced by the changes caused by induced plant defense mechanisms. This variation was not observed in plant chemistry, as C:N did not vary between damaged versus undamaged leaves. Possible explanations for this include the reabsorption of nutrients prior to leaf shedding, a concentration of defense chemicals towards more sensitive parts, or that soil invertebrates are more influenced by changes in the root region. C:N varied significantly among plant species and sampling periods, and the ratio of browsed branches one year after treatment differed among treatment groups and plant species. Treated dune willow shrubs had a reduced number of browsed branches, indicating a possible whole-plant response. This study displays the importance of preserving these unique system composed of an arid environment with relatively homogenous soils and redundant vegetation, such as the Albany Pine Bush, which allow for an exceptional opportunity to investigate plant-soil interactions. |
