new zealand mangroves as a model system for studying tree ... · new zealand mangroves as a model...
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New Zealand mangroves as a model system for studying tree
carbon and water relations Jarrod Cusens and Sebastian Leuzinger
Forests and carbon
• Forests/trees dominate global terrestrial carbon cycle
• Almost all carbon that enters terrestrial systems passes through trees
• About 70-90% aboveground C is in forests
Studying natural systems
Observational
• Complex
• Unpredictable
• Uncontrollable
Greenhouse experiments
• Not always representative
• E.g. seedlings and saplings
Mangrove survival
• The intertidal zone is harsh and a stressful place for plants
• The two major stressors are:
1. Salt stress
2. Water logging anoxic soils
Mangrove survival strategies
• Salt exclusion at the roots via ultrafiltration
• Salt excretion at the leaves
• Pneumatophores (aerial roots)
• Vivipary
• Successive cambia
http//www.nzpcn.org.nz Photo: John Sawyer
Mangrove survival
• Salt exclusion at the roots (about 90% of the salt)
• Salt excretion at the leaves (40% of remaining salt)
• Pneumatophores (aerial roots)
• Vivipary
• Successive cam
Mangrove survival
• Salt exclusion at the roots (about 90% of the salt)
• Salt excretion at the leaves (40% of remaining salt)
• Pneumatophores (aerial roots)
• Vivipary
• Successive cam
http://en.wikipedia.org/wiki/Mangrove
Mangrove survival
• Salt exclusion at the roots (about 90% of the salt)
• Salt excretion at the leaves (40% of remaining salt)
• Pneumatophores (aerial roots)
• Vivipary
• Successive cam
Mangrove survival
• Salt exclusion at the roots (about 90% of the salt)
• Salt excretion at the leaves (40% of remaining salt)
• Pneumatophores (aerial roots)
• Vivipary
• Successive cam
http//www.nzpcn.org.nz Photo: John Barkla
http//www.nzpcn.org.nz Photo: John Barkla
Mangrove survival
• Salt exclusion at the roots (about 90% of the salt)
• Salt excretion at the leaves (40% of remaining salt)
• Pneumatophores (aerial roots)
• Vivipary
• Successive cambia with secondary growth (84.9% of trees and shrubs that exhibit this are water or salt stressed)
Why mangroves?
1. Mangroves are not classically water stressed because they grow in the tidal zone
2. Tidal inundation with salt water induces periodic and predictable stress conditions
3. No extremes in temperature (i.e. no freezing)
4. Little or no nutrient limitation
5. Forests are monospecific so there is no interspecific competition
6. Their canopies are easily accessible even when trees are mature
New Zealand mangroves
• Avicennia marina subsp. australasica
• Most wide-spread species globally
• In contrast to global trends NZ mangroves are expanding/spreading
Two areas of interest 1. Water
– Water relations of trees in relation to diurnal, tidal and seasonal rhythms and, environmental conditions?
– Do mangroves use alternative water uptake mechanisms?
2. Carbon
– What factors limit growth in mangroves on various temporal scales and environmental conditions?
– How much carbon do they store as they grow?
Study Design • Three different sensors for water use
• Stem growth + NSC
• Climatic sensors
• Soil sensors
Site selection
• We had several criteria
• The middle of the whole system Eddy-flux
• Uniform tree size
• Minimal edge effects
Environmental variables
• Sunlight
• Temperature
• Humidity
• Soil moisture
• Rainfall
• Salinity
• Tide height and timing
Water relations sensors A. Sap-flow
− Sap-flow sensors
B. Leaf water-potential − ZIM-probes
C. Stem-diameter fluctuation − Dendrometers
http://www.zim-plant-technology.com
ZIM-probes for leaf water-potential
Alternative water uptake
salt water ca. -2.5 MPa
dry air ca. -90 Mpa
xylem water potential ca. -3 Mpa ?
leaf water potential ca. -3.5 Mpa
root water potential ca. -2.7 Mpa ?
according to cohesion theory:
Alternative water uptake
salt water ca. -2.5 MPa
dry air ca. -90 Mpa
xylem water potential ca. -3 Mpa ?
leaf water potential ca. -3.5 Mpa
root water potential ca. -2.7 Mpa ?
according to cohesion theory:
alternative theory: water uptake through hygrophillic mucilage plugs to avoid such low xylem water potentials? Active water transport through xylem mucilage linings?
Alternative water uptake
salt water ca. -2.5 MPa
dry air ca. -90 Mpa
xylem water potential ca. -3 Mpa ?
leaf water potential ca. -3.5 Mpa
root water potential ca. -2.7 Mpa ?
according to cohesion theory:
alternative theory: water uptake through hygrophillic mucilage plugs to avoid such low xylem water potentials? Active water transport through xylem mucilage linings?
but: water in meta-stable status when under -3 Mpa !
• Epistomal mucilage plugs?
• Xylem mucilage linings?
Zimmermann et al (2007) Protoplasma 232: 11–34
Carbon and growth • When do mangroves grow? • Two main measurements
– Stem growth – Non-structural carbohydrates
NSCs CO2
NSCs
NSCs
Looking ahead
• Litterfall already started
• Fertilisation planned in the next year
• Eddy-flux installation this year
• Multifactor: CO2 enrichment/FACE x Warming x Fertilisation – To date only short CO2 experiments have been done
in mangroves
• Mangrove ‘LTER’? – characterisation of the whole system/multidisciplinary
Follow us
Track our data in real time:
http://haze.decentlab.com/aut-deployment-001/
Blog:
http://thehipecologist.wordpress.com/
@jcusens