Authors: Kelly San Antonio, Makenzie (Jennifer) Holifield, Hailong Huang, Devin Jen, Kodi Feldpausch, Wei Wu – University of Southern Mississippi
Title: The impact of inundation and nitrogen on common saltmarsh species using marsh organ experiments
Abstract: Sea level rise is an escalating threat to saltmarsh ecosystems as increased inundation is a well-documented stressor for marsh plants, with consequences such as decreased biomass, lowered productivity response, and plant death. The other potential stressor is elevated nitrogen, which may stimulate new plant growth but also has a controversial impact on belowground biomass and therefore can affect the stability of saltmarshes. This is particularly relevant due to the extra amount of nitrogen brought into coastal regions via freshwater diversions. Our research objective is to examine the combined effects of inundation and nitrogen on common saltmarsh plants (Spartina alterniflora and Spartina patens). We set up two marsh organs with six rows and eight replicates in each row, one planted with Spartina alterniflora, the other with Spartina patens in the Pascagoula River. We randomly selected four replicates in each row to add 25 g/m2 of nitrogen in the form of ammonium nitrate every two or three weeks in the growing season. With the same frequency, we collected morphological characteristics such as plant height, leaf count, and stem count to represent vegetation conditions in different dimensions. We developed multilevel Bayesian models to evaluate how inundation and nitrogen affected these characteristics. The results show plants with the nitrogen addition in both species generally tend to have higher productivity when compared to non-fertilized plants. In addition, the different plant characteristics have shown various responses to inundation in the short and long term, indicating potential energy tradeoffs. More so, S. alterniflora appears to adapt better to increased inundation than S. patens. This modeling work will facilitate more-informed restoration and conservation efforts in coastal wetlands while accounting for climate change and sea-level rise.