Session 4
Connecting Individual-Level Physiology to Large-Scale Productivity
Papers to Read Before!
Litchman 2015: A trait-based perspective on global phytoplankton ecology
Finkel 2009: Review of elemental stoichiometry & global implications
Cell Size and Elemental Stoichiometry: The Keys to the Kingdom
In the review by Finkel et al. (2009), the paper is advocating for an elemental view of phytoplankton’s response to climate change via a focus on two essential areas of study. The first is the size of the cell, and the second is its elemental stoichiometry. The authors argue that tracking these key features is the way forward to understanding how much carbon can be fixed and exported under nutrient limitation.
Phytoplankton community structure itself can dictate the amount of carbon being exported to the deep ocean, which is what necessitates in-depth studies of the responses of individual functional types to global change. By exploring specific responses, models can be updated to reflect real-time changes in phytoplankton communities.
The necessity of studying cell size as a proxy for phytoplankton metabolic potential is further supported by the fact that there are many metabolic properties that show a power-law relationship with phytoplankton cell size, namely that the size of the phytoplankter is fundamentally controlling some metabolic rate via the relationship:
The discovery of numerous metabolic rates that follow this relationship has further supported the role of cell size in determining organismal metabolism.
Global Change Stressors and Stoichiometry
Multiple stressors have been found to have a marked impact on phytoplankton cellular stoichiometry. Among these are:
Carbon dioxide
Temperature
Nutrients
Light
(in short, all the usual suspects when it comes to phytoplankton ecology).
Traits and ecosystem stress
Functional types are defined by their differences in collections of effect and response traits.
Effect traits
Traits that affect global biogeochemical cycles
Response traits
Traits that determine how abundance responds to environmental conditions
A key example of a response trait is temperature, since temperature influences phytoplankton, but phytoplankton can’t (easily) influence temperature.
Coccolithophores
220 million years ago = first appearance in fossil record
if ocean floor is lower than carbonate compensation depth, liths dissolve & less carbon is exported
DMSP producers = cloud condensation nuclei
Diatoms
160-200 million years ago, but most diversification in the last 60 million years
silica shells
store nutrients in vacuoles supported by silica shell
low N:P ratios
Dinoflagellates
over 200 mya, but less diversity over the past 40-60 million years
symbionts, mixotrophy, bioluminescence, and other highly diverse characteristics
NPZ Models
Historically have dominated, and characterize the phytoplankton as a single pool responsible for chowing down on the major limiting nutrient (often N). Gross simplifications, but often useful nonetheless.