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
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
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
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
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
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?