OUTLINE

What is a macronutrient?

Trends in nutrients & limitation

The N cycle – sources, sinks and recycling

Silicate – the body builder

Stoichiometry - The N and P cycles

Climate change & macronutrients

Macronutrients in the

ocean

Philip Boyd

NIWA/OTAGO, New Zealand

September 2011

What is a macronutrient?

“An element, such as carbon, hydrogen, oxygen, or nitrogen,

required in large proportion for the normal growth and development of a plant”

What are they required for?

The synthesis of macromolecules such as lipids, proteins and carbohydrates

NOAA 1994, Levitus

Joseph Wright

THE ELEMENTS OF

MICROBIAL LIFE Component Composition

Nucleus (DNA) C-N-P

Ribosome (RNA) C-N-P

Membranes C-P

Cell wall C-N

Proteins/enzyme

s/

flagellum

C-N

Storage bodies:

• PHB

• Poly-P

C

P

The elements required for each macromolecular group are defined

by the structure of the molecule, e.g. nucleotides comprise a

phosphate group, a carbohydrate molecule and a N-containing base

Capone 1992

Many complex pathways after nutrient uptake

Vmax2

Ks1 Ks2

Substrate concentration (S)

Upta

ke r

ate

(V

)

Nutrient uptake kinetics

Active uptake by membrane transporters

Internal storage pool

½ Vmax1

Vmax1

½ Vmax2

Global nutrient distributions - Phosphate

Global

Nutrient

distributions

Nutrient limitation patterns - Diatoms

(Moore et al., 2004).

Nutrient limitation patterns – N fixers

The Biogeochemical cycle of N in the ocean

Lipschultz et al. (2000)

N2 FIXATION

Discovered in late 19th century in soil bacteria

H. B. Bigelow (1931): “The possibility that so-called N2 fixers may also fertilize seawater must be taken into account”

Dugdale discovered N2 fixation in Sargasso Sea in 1961

Process was considered to be negligible in the 1980’s, but significant since JGOFS

Boyd &

Hurd

(2009)

N2 FIXATION AT STATION ALOHA

(1990-2000)

N2 accounts for 47±9% of “new” N

Large interannual variations:

36% in 1993 vs. 69% in 1999

Relative importance of N2 vs. NO3- as a

source of new N has increased since

1995

Karl et al. (2002)

Boyd & Hurd Figure 6

NO3 (µmol L-1)

0 5 10 15 20 25D

ep

th (

m)

0

50

100

150

200

250

winter 2004

spring 2005

summer 2005

autumn 2005

Sinks for N

Seasonal trends in nutrient profiles

Boyd & Hurd (2009)

N preferences

at HOT - SPSG

• Prochlorococcus

prefers NH4+/DON but

some phylotypes can

use NO2-

• Eukaryotic phototrophs

use NO3- and possibly

DON, and compete

with all others for NH4+

• Heterotrophic bacteria

may prefer NH4+/DON

but can also use NO3-

/NO2-

• Diazotrophs use N2

Slide – courtesy D. Karl

THE FOODWEB AND NITROGEN CYCLING

f ratio = (new N/(new N + regenerated N))

An N Cycle summary - an annual budget

Karl et al. (2002)

The biological pump recycles macronutrients

7-16 gT C yr-1

45-50 gT C yr-1

It is in balance over long timescales

(years) as:

PON

export

NO3

Eppley & Peterson (1979)

Nutrient remineralization

length scales

N

C

Si

Fe

depth

Export

Role of bacteria

“Classic” von Brand & Rakestraw diatom – rotting

experiment of 1935!

nitrification

• A typical

nutrient profile

Why such a difference in

These nutrient profiles?

Regional differences due to

age of the water mass

Determines “potential

productivity” of the basin

Arrigo (2005)

Silicate – the body builder

Courtesy Mary Silver (UCSB)

Hamm et al. (Nature 421, 841-843)

Architecture and material properties of diatom shells

provide effective mechanical protection

The evolutionary arms

race between diatoms

and their specialized

predators will have had

considerable influence

in structuring pelagic

food webs and

biogeochemical cycles

Frustules are remarkably strong by virtue of their architecture

and the material properties of the diatom silica

Broken diatom frustules are indicators of mortality

Fragilariopsis kerguelensis

Discoid diatoms

Courtesy V. Smetacek (AWI)

0 5 10 15 20

mm

ol

m-3

d-1

0.0

0.2

0.4

0.6

0.8

1.0nitrate depletion

silicic acid depletion

Days

Fe supply impacts the uptake stoichiometry of silicate relative to nitrate

And SILICIFICATION

Boyd et al. (2005)

+Fe -Fe

Under low Fe diatoms produce thicker

frustules

Biogenic silica / opal - mineral ballast – particle sinking

Radiolarian

Diatom Phaeodarian

NOAA 1994

Levitus

Global distribution of silicate

V. Smetacek (AWI)

Insights into diatom blooms in the geological

past are obtained from sediment cores

Marked increases in productivity & rapid settling of biogenic matter are

suggested in cores by the episodic accumulation of diatomaceous oozes

up to 1 m thick!

Ocean biogeochemical cycle of Silica (Trequer et al. 1995)

Rivers

5.0

Eolian 0.5

Mixed layer

Hydrothermal

0.2

Upwelled

114.5

240

120

90.9

29.1

6.1

0.4 basalt

23

Teramoles of Si /year

Biol.

Uptake

And recycling

Nutrient Stoichiometry - The N and P cycles

Stoichiometry refers to patterns of mass balance in chemical conversions

of different types of matter, which often have definite compositions.

Sterner and Elser (2002)

Further definitions

• Ecological stoichiometry--The balance of multiple chemical substances in ecological interactions and processes.

• Elemental imbalance--Dissimilarity in nutrient content between two things, such as between an autotroph and the inorganic medium.

If a consumer and resource have identical stoichiometry, they are perfectly balanced. The greater they differ, the more their imbalance.

Sterner & Elser (2002)

REDFIELD STOICHIOMETRY OF LIFE

C106:N16:P1

Carbon

Nitrogen

Phosphorus

C:N = 6.6 / C:P = 106 / N:P = 16

REDFIELD STOICHIOMETRY OF LIFE

C106:N16:P1

Carbon

Nitrogen

Phosphorus

Initially thought to be the imprint of the synthesis of

macromolecules including lipids, proteins and carbohydrates

• Redfield (1934)

N:P = 20

• Cooper (1937/1938)

N:P ratio redefinition

based on salt

correction

of 1.35x for P

analyses!

• Today N:P = 15-16

Atlantic

Ocean

N:P = 20

Redfield (1934)

“THE RATIO”

Courtesy D Karl

• C:N:P is plastic, not fixed

• N P limitation transition much higher than

16:1

General conclusion: “Our analysis suggests caution in

application of the Redfield Ratio in theoretical biogeochemical

analyses and as a conversion factor in field studies.”

R. Geider and J. La Roche (2002)

Redfield revisited: variability of C:N:P in marine

microalgae and its biochemical basis

Eur. J. Phycol. 37: 1-17

Klausmeier et al. (2004)

Their results show that “the canonical Redfield

N:P ratio of 16 is not a universal biochemical

optimum, but instead represents an average of

species-specific N:P ratios.”

Klausmeier et al. (2004)

N:P ratios and physiological strategies

Arrigo (2005)

Experimental Variation of the C:N:P Ratios (by Atoms)

in Cultures of the Freshwater Alga, Chlorella

pyrenoidosa

(Ketchum and Redfield, 1949)

Conditions C N P

Normal cells 47 5.6 1

Phosphorus deficient

cells

231 30.9 1

Nitrogen deficient cells 75 2.9 1

•Elemental imbalance--Dissimilarity in nutrient content between an autotroph

•and the inorganic medium.

N:P differences are evident within the biogeochemical cycles

Arrigo (2005)

Using the Redfield ratio perspective – i.e. P*

Basin-scale differences

North Atlantic P* < 0, P limited

South Atlantic P* > 0, N limited Moore et al. 2008

Are changes in P* due to N fixation or N:P uptake of other phytoplankton?

STA. ALOHA

• EZ SRP has decreased by >80% over past 17 years

• How low can it go?

CASE STUDY

STA. ALOHA

Climate change and macronutrients

Boyd and Doney

(2002)

Doney (2006)

Figure 2a. Total NOy+NHx Deposition in 1860, mg N m-2 yr-1

Figure 2c. Total NOy+NHx Deposition in 2050, mg N m-2 yr-1

Duce et al. 2008

Anthropogenic AN provides around 32% of external N supply

S

u

c

h

More N fixers

Due to warming?

Boyd & Doney (2002)

A)Co

cco

lith

oph

ore

cel

ls m

L-1

0

20

40

60

80

100

120

B)

Cal

cite

pro

duct

ion r

ate

(g C

(g C

hl a

-1)

d-1

)

0

1

2

3

4

5

C)

pCO2

19 Pa 39 Pa 76 Pa

N2

fix

atio

n r

ate

(nm

ol

N

mo

l C

-1 h

-1)

0

1

2

3

4

D)

pCO2

19 Pa 39 Pa 76 Pa

N2

fix

atio

n r

ate

(nm

ol

N

mo

l C

-1 h

-1)

0

1

2

3

4

Ambient

High CO2High Temperature

Greenhouse

Ambient

High CO2High Temperature

Greenhouse

Hutchins et al. (2007)

Other environmental controls on N fixers?

Moisander et al. (2010)

What is needed

Surveys – e.g. AMT

And new modelling approaches

Follows (2007)

Conclusions

Macronutrients play a key role in setting the

productivity of the oceans

Their biogeochemical cycles are tightly

interlinked via stoichiometry – yet they are

also flexible

Other factors such as trace element

supply and climate-mediated changes

can subtly alter these links

Climate change will impact the

biogeochemistry of macronutrients in a

complex manner