Belowground Biomass of Spartina alterniflora: Seasonal Variability and Response to Nutrients

• Main Author: Darby, Faith Armand
• Other Authors: R. Eugene Turner
• Format: Others
• Language: en
• Published: LSU 2006
• Subjects: Oceanography & Coastal Sciences
• Online Access: http://etd.lsu.edu/docs/available/etd-11142006-125308/

Spartina alterniflora is a salt marsh macrophyte found from Canada to the Gulf of Mexico which often provides the dominant plant cover. Although S. alterniflora is well known for its high aboveground productivity, fifty to ninety percent of the total plant production occurs belowground. No previous studies address the seasonal variation of belowground biomass or the response of above-and belowground biomass to nutrients at the southern limits of its U. S. range. The objectives of this study were to: 1) document the seasonal variability of its above- and belowground biomass and test for responses to various combinations of N, P, and Fe supplements, 2) test the usefulness and variability of three functional indicators of nutrient use efficiency, resorption efficiency, resorption proficiency, and, 3) compare nutrient limitation controls in East coast and Gulf of Mexico salt marshes. Various combinations of N additions resulted in more aboveground biomass, higher stem densities and longer stem lengths, but had no effect on the amount of belowground biomass. No change in the aboveground biomass observed when P was added, but there was a decrease in the live belowground biomass. The average N : P molar ratios in the above- and belowground tissues, and three resorption indices supported the hypothesis that the accumulation of biomass aboveground was limited by N, and by P belowground. Higher soil respiration and a lower Eh are anticipated additional soil property changes with nutrient enrichment. The observations from these field trials formed a unified conclusion, which is that the widespread effects of coastal eutrophication leads to lower root and rhizome biomass, belowground production, and organic matter accumulation. The cumulative effects of increased nutrient loadings to salt marshes may be to decrease soil elevation and accelerate the conversion of emergent plant habitat to open water, particularly at the lower elevation range of the plant. These results support management actions supporting coastal marsh conservation through: 1) reducing nutrient loading to coastal zones and not diverting more nutrients to coastal marshes, 2) solving water quality problems with a multiple nutrient approach, and, 3) choosing monitoring metrics based on both belowground and aboveground plant production.