Lecture 1. Fundamentals of nutrient limitation: Consilience of plant ecophysiology andConsilience of plant ecophysiology and ecosystem science
Benjamin Z. HoultonAssociate Professor of Global Ecology and BiogeochemistryDepartment of Land, Air and Water ResourcesUC Davis
[email protected] • houlton.lawr.ucdavis.edu • @benhoulton #houltonlab
Human N t i t Societies
Food security
NutrientCycling
Nutrient limitation
EcosystemFunctioning/
ClimateChange, C Cycling
StabilityChange, C Cycling
OutlineOutline
Part 1 Nutrient limitation definedPart 1. Nutrient limitation defined‐ Perspectives, theory: 3 essential concepts2 f i li i i dPart 2. Patterns of nutrient limitation and
controls‐ Nitrogen limitation and controls‐ Phosphorus limitation and controlsp‐ Co‐limitation, feedback and maintenance
Part 1. Nutrient limitation definedPart 1. Nutrient limitation defined
General Definition (direct assessment):General Definition (direct assessment):Nutrient limitation occurs when meaningful additions of an essential element inadditions of an essential element in biologically available forms cause an increase in the rate of a biological process (such as primary productivity) and/or in the size of an important ecosystem compartment (such as bi )biomass).
(after Vitousek et al. 2010)
For exampleFor example…
Vitousek and Farrington, 1997
Indirect assessmentsIndirect assessments
l b l l (1. Nutrient availability in soil (Powers1980)
2. Plant investments in acquiring particularnutrients (Harrison and Helliwell 1979)
3. Tissue concentrations or ratios of elements (van den Driessche 1974, Koerselman and M l 1996)Meuleman 1996).
For example…For example…
Nutrient Resorption
Leaf fallLeaf fall
Reed et al., New Phytologist, 2012
Concept A. Single LiebigConcept A. Single LiebigThe "law of the minimum“: the environment is unlikely toprovide resources in the precise proportions required, at anyprovide resources in the precise proportions required, at any given site a plant should be limited by the single resource in lowest supply relative to need. A plant should increase growth in response to addition of its one limiting resource until it becomes limited by some other resource.
After Gleeson and Tilman, 1995
Justus von Liebig
Concept B. Optimization theoryConcept B. Optimization theory
Optimization theory: plants should vary inOptimization theory: plants should vary in physiology and morphology so as to avoid excess foraging for a non‐limiting resource g g gand to maximize effort expended inthe acquisition of a limiting resource.
After Gleeson and Tilman, 1995
Gleeson and Tilman, 1995
Concept C. Multiple Resource ( )Limitation (MRL)
Multiple resource limitation (MRL), which occurs when theaddition of any one of several resources causes anincrease in production and/or biomass.
Three general pathways:Three general pathways: a. Physiological processes within plants – e.g., Root/shoot adjustmentsb. Positive interactions in resource supply – e.g., N stimulates P
mineralizationLi i i f diff i f i l i hic. Limitation of different species or functional groups within an ecosystem by different resources – e.g., N fixers P limited, non‐fixers N limited
after Vitousek et al. 2010; see Bloom et al. 1985
Case study: The Problem of N fixationCase study: The Problem of N fixation
BiomeMature Boreal ForestMature Temperate
Woody LegumesAbsentAbsent
ForestLowland Tropical ForestSavanna
10 – 49%6 – 56% (ter Steege et al. 2006)
(Cleveland et al. 1999)
Phosphatase enzymep y
Houlton et al. Nature 2008
Proposed feedback between N fixation, N limitation, P limitation and biochemical P mineralizationP limitation, and biochemical P mineralization
N fixation turns on
N demands decreaseN demands increase
P mineralization enzymes i P il biliincrease, P availability increases
P becomes limiting
Phosphatase activity
ratio 0.004
0.005
0.0
af P
:C
0.002
0.003 0.2 0.4 0.6 0.8
0.02 0.04 0.06 0.08 0.10
Lea
0.001
Leaf N:C ratio0.02 0.04 0.06 0.08 0.10
Wang, Houlton, Field, GBC, 2007
Houlton et al. Nature 2008
Simulation 1 = phosphatase plus energetic constraint on N fixation
11
0
50(d
egre
e)
7
9
-50
0
Latit
ude
3
5
-150 -100 -50 0 50 100 150Longitude (degree)
-1
1Wang and Houlton, 2009
(Cleveland et al. 1999)
Part II Patterns of nutrient limitationPart II. Patterns of nutrient limitation and controls
Nitrogen limitation is widespread
Lebauer and Treseder, Ecology, 2008
…but so is P……but so is P…
Elser et al., Ecology Letters, 2008
Ecosystem‐scale mechanisms of N ylimitation
after Vitousek et al. 2010
Availability independent losses of N and the imprint of humans on the global Ngcycle
Modified from Perakis and Hedin, Nature,2002
Case Study: HBEFLikens and Bormann, 1995
Natural vs Anthropogenic DisturbanceNatural vs. Anthropogenic Disturbance
Houlton et al., Ecosystems, 2003
Constraints toConstraints to N2 fixation
0 8
1.0
0.4
0.6
0.8
0.0
0.2
Reed et al., Eco Mon., 20120 5 10 15 20 25 30 35 40 45 50 55
Houlton et al., Nature, 2008
Reed et al., Eco Mon., 2012
Ecosystem‐scale mechanisms of P llimitation
Vitousek et al. 2010
Depletion‐driven P limitation:Depletion driven P limitation:“The Walker & Syers model”
Case Study: Ecological StaircaseCase Study: Ecological Staircase
Hans Jenny
T1 T3 T5T4T2T1 T3 T5T4T2
Izquierdo, Houlton, and van Huysen, Plant and Soil, 2013
Anthropogenic P limitationAnthropogenic P limitation
Vitousek et al. 2010
Nutrient cycling interactions and synergy
• P by N interaction in lakes etcP by N interaction in lakes, etc• Phosphatase enzymes: N by P interactions on landland
N2 fixation+ + Decreased
N availabilityIncreased
P availability
Lake 267
Lake 226
Schindler, Science, 1977
Phosphatase: N by P interactionPhosphatase: N by P interaction
‐ Class of enzymesthat cleave ester‐bonded P making it available forP making it available for uptake.
‐Global meta‐analysisd t h i idata show an increase in plant and microbial phosphatase with added N, a decrease with added P.
Marklein and Houlton, New Phytologist, 2012
SummarySummary
• Nutrient limitation is widespread observedNutrient limitation is widespread, observed directly and indirectly.
• Three concepts: Single “Liebig”; Optimization;• Three concepts: Single Liebig ; Optimization; Multiple Resource LimitationUl i l b l d i• Ultimately, mass‐balance determines limitation by N and P
• Synergies can (and do) alter patterns of N and P co‐limitation
