Nutrient Limitation in Northern Gulf of Mexico (NGOM): Phytoplankton Communities and Photosynthesis Respond to Nutrient Pulse

Yan Zhao,Antonietta Quigg,Douglas Andrew Campbell

doi:10.1371/journal.pone.0088732

Yan Zhao, Antonietta Quigg + Show 1 more

Open Access

https://doi.org/10.1371/journal.pone.0088732

Copy DOI

Journal: PloS one	Publication Date: Feb 14, 2014
Citations: 36	License type: CC BY 4.0

Affiliation: Texas A&M University, Texas A&M University at Galveston

Abstract

Although the Mississippi-Atchafalaya River system exports large amounts of nutrients to the Northern Gulf of Mexico annually, nutrient limitation of primary productivity still occurs offshore, acting as one of the major factors controlling local phytoplankton biomass and community structure. Bioassays were conducted for 48 hrs at two stations adjacent to the river plumes in April and August 2012. High Performance of Liquid Chromatography (HPLC) combined with ChemTax and a Fluorescence Induction and Relaxation (FIRe) system were combined to observe changes in the phytoplankton community structure and photosynthetic activity. Major fluorescence parameters (Fo, Fv/Fm) performed well to reveal the stimulating effect of the treatments with nitrogen (N-nitrate) and with nitrogen plus phosphate (+NPi). HPLC/ChemTax results showed that phytoplankton community structure shifted with nitrate addition: we observed an increase in the proportion of diatoms and prasinophytes and a decrease in cyanobacteria and prymnesiophytes. These findings are consistent with predictions from trait-based analysis which predict that phytoplankton groups with high maximum growth rates (μmax) and high nutrient uptake rates (Vmax) readily take advantage of the addition of limiting nutrients. Changes in phytoplankton community structure, if persistent, could trigger changes of particular organic matter fluxes and alter the micro-food web cycles and bottom oxygen consumption.

Highlights

Liebig’ law of minimum first claimed that plant growth is not determined by the total amount of a resource, but instead limited by the scarcest resource (Liebig 1840 in [1])
We focused on the short-term (48 hr) response of phytoplankton communities under ambient conditions to changes only by the addition of nutrients, including nitrogen, organic and inorganic phosphate as well as a ‘bottom’ water sample
Active radiation (PAR) was highly variable reflecting sunny versus cloudy days at sea

Summary

Introduction

Liebig’ law of minimum first claimed that plant growth is not determined by the total amount of a resource, but instead limited by the scarcest resource (Liebig 1840 in [1]). Tilman et al [2] resource ratio theory set up the basis for understanding use/competition for nutrient concentrations or ratios and phytoplankton community structure. Grover [3] established the variable-internal-stores model to offset the drawback of the applicability of Tilman’s theory in non-steady states The intermediate disturbance hypothesis emphasized that periods of nutrient pulse could control the variability of phytoplankton community structure [4]. All these theories have been tested in laboratory and natural aquatic systems (mostly freshwaters) Complex nutrient conditions in coastal environments lead to corresponding variability of phytoplankton community structure. It has been suggested that spring phytoplankton blooms are the initial step in the scenario of the development of annually bottom hypoxia [8]

Methods

Results

Conclusion