Phosphorus, nutrient, carbon and water interactions.

Jason Neff

Geosciences Dept, CU Boulder

What controls primary productivity?

N

P P PCa, MgFe

H2OH2O H2O

Short vs. long term limitations

Limits to Production

• Light

• CO2

• Temperature

• Moisture

• Nutrients

Linked by physiology/biochemistry…

Tradeoff water for CO2 etc.

Different set of constraints…

Commonly viewed as a separate type of limitation but…

Nutrients as a limitation

Justus von Liebig: “Liebig’s law of the minimum”

~1850:

Yield (growth) is proportional to the amount of the most limiting nutrient, whichever nutrient it may be.

Start of the green revolution & clearly linked plant growth rates to the amount of mineral nutrients present.

The physiology of nutrient limitation

Redfield Ratios: Alfred Redfield (Woods Hole)

Basic Observation: Biologically active tissues tend to have relatively constant proportions of elements. Observation based on oceans but “generally” holds in terrestrial systems as well

C : N : P : Fe = 106 : 16 : 1 : 0.01

Early Succession – abundant rock-derived minerals (e.g. P, Mg, Ca etc). Very little N.

Mechanisms for N limitation IN fixers dominate in early

succession

N fixation is energetically expensive

Fixers can’t control the flow of N (some ends up in soils)

Other plants take advantage of added fertility and outcompete fixers for light, other nutrients (P)

Alder thicket – interior Alaska

One reason why N limitation is so common in temperate ecosystems

Piapatite

Pioccluded

Pinon-occluded

Po

Ptotal

Time

g P

/ u

nit

are

a p

rofi

le

From Walker and Syers 1976

Bedrock weathering can cause different limitations to develop

Long term P changes

Chadwick et al, 1999

N Limitation or

NP colimitation

P limitation

Crews et al, 1995

Is P limitation pervasive in the tropics?

Carl Bern et al – uplift regenerates soils and nutrient supply

Steve Porder et al – Erosion and downcutting regenerates soils

Volcanic Tropical soils can be very nutrient rich

Why aren’t all terrestrial systems P limited?

NO3-

?X

NO

NH3

N2O

DON

Does it make sense to talk about single- element limitation?

•Metals    7 MG ions    2 CL ions    30 FE ions    2 MO ions

N fixation is linked to other elements (including P)

Nitrogenase enzyme

Microorganisms can be P limited even when plants are N limited (Cory Cleveland et al)…

So what does that mean?

Nutrients vs. WaterP

rimar

y P

rodu

ctio

n (g

m-2)

Annual Rainfall (mm)

0 100 200 300 400

050

0 10

0015

00

Actual Production

Potential P

roduction

From Penning de Vries and Djiteye, 1982

Nutrient Limitation

Nutrients vs. Water

N availability and loss are tied to moisture

N delivery (deposition) and fixation are tied to moisture

Changes in precipitation can influence production through the N cycle, particularly following perturbations

Summary

N is not the only element that limits productivity. P in freshwater, oceans and tropical systems

Metals (Fe) in oceans

Base cations in some tropical settings

Water-Nutrient interactions are complex There isn’t a clear distinction between a nutrient limited vs.

water limited ecosystem

Changes in water often influence ecosystems via the N cycle

Nutrient input/output balance

Dust coming off the Sahara Chadwick et al, 1999

P in Dust

Dust contains mineral aerosols and often is generated in deserts (lots of CaPO4)

Once deposited, dust can weather and contribute P to a soil. In very old systems, this is probably the only source of P to the ecosystems

Dust and the Mountains of the Western US

Dust Deposition in San Juan Mountains

1999

2004

2003

5.3X

5.3X

5.7X

Sediment loading increased ~ 200 years ago

Dust Provenance

~200 years

~3000 years

~200 years

~3000 years

Sed. Rate (g m-2 sediment yr-1)Porphyry Tarn : Senator Beck

Tarn

Areal Flux (g m-2 yr-1)Porphyry Tarn : Senator Beck

Tarn

KContemporary1900-1920Historic

8.09 : 8.0416.83 : 12.832.89 : 2.48

0.97 : 1.732.03 : 2.77

0.35 : 0.0.54

MgContemporary1900-1920Historic

2.42 : 1.365.24 : 0.660.65 : 0.19

0.29 : 0.290.63 : 0.140.07 : 0.04

CaContemporary1900-1920Historic

3.11 : 1.013.88 : 0.750.44 : 0.19

0.37 : 0.220.47 : 0.140.05 : 0.04

PContemporary1900-1920Historic

0.60 : 0.310.44 : 0.300.05 : 0.05

0.07 : 0.070.05 : 0.060.01 : 0.01

How do changes in non-limiting nutrients affect ecological function?

What does it mean that P deposition has increased 7X relative to background rates?

What role does the deposition of base cations play in soil development and stream chemistry?

Summary

There are human perturbations to most of the biologically-relevant element cycles on earth.

For many of these perturbations (e.g. P, Ca, Mg etc), we lack basic information on the magnitude of change and the potential biological impacts.