How herbivores and nitrogen addition affect developing soils of Mount St. Helens
Abstract
The volcanic eruption of Mount St. Helens (MSH) on May 18, 1980 removed all legacies of life and organic matter. Interactions between plants and microbes largely dictate the development of soil C and nutrient cycles. We investigated the role of plant herbivores and N-addition on two aspects of soil development. Using a long-term experiment of N-addition and herbivore exclusion from the keystone woody plant, Salix sitchensis, across two sites (west and east) we measured soil pH and moisture. We hypothesized that plots with N-addition would have a lower pH than ambient plots and the presence of herbivores would decrease soil moisture. The pH was acidic ranging from 5.4 to 5.9 but there were no differences in pH across the sites or treatments. Moisture was greater in west plots (25.5% ± 0.07) than the east (45.4% ± 0.06) but did not vary by treatment in either site. East plots might have lower moisture due to their greater slope and westward aspect. In previous work we showed that weevils respond positively to host drought stress. Hence the difference in soil moisture, and corresponding drought stress, may explain the >2x greater stem damage by weevils in the east plots (58% of basal area attacked) compared the west plots (26% of basal area attacked). The acidic pH might have implications for the composition of microbes and the rates of decomposition which will have feedbacks to soil C and N cycling. Further work will quantify soil carbon and nitrogen responses.
About the Presenters
Annamaria Pacheco
My name is Annamaria Pacheco. I am a single mother of a beautiful 4 years son named Jett. I am a senior studying environmental science at WSUV. I am fortunate to have the opportunity to work in Dr. John Bishop’s ecology lab where I have been able to develop my research skills and interact with some dynamic people that have help me to grow both personally as well as academically. I hope to continue my work at WSUV as it is an integral part of my future career goals.