New Zealand mangroves as a model system for studying tree carbon and water relations Jarrod Cusens and Sebastian Leuzinger
CO 2 H 2 O Carbon and water are tightly coupled
Transpiration contributes ca. 80-90% of terrestrial evapotranspiration
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
Transpiration clouds over the Amazon
Transpiration clouds over the Amazon
Studying natural systems Observational Greenhouse experiments Complex Unpredictable Uncontrollable Not always representative E.g. seedlings and saplings
Costly Swiss Canopy Crane Project
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)
Robert et al. 2011 PLOSOne 6:1 1-10
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
Monospecific Tide line
Low canopy at maturity
New Zealand mangroves Avicennia marina subsp. australasica Most wide-spread species globally In contrast to global trends NZ mangroves are expanding/spreading
1. Water Two areas of interest 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
ZIM-probes for leaf water-potential http://www.zim-plant-technology.com
Three trees with three of each sensor ZIM-probes Base station 3 x Sap-flow 3 x Dendrometer
Aluminium scaffolding system
Powered with a wind generator Central logger and battery pack
Alternative water uptake according to cohesion theory: dry air ca. -90 Mpa leaf water potential ca. -3.5 Mpa xylem water potential ca. -3 Mpa? root water potential ca. - 2.7 Mpa? salt water ca. -2.5 MPa
Alternative water uptake according to cohesion theory: dry air ca. -90 Mpa leaf water potential ca. -3.5 Mpa alternative theory: water uptake through hygrophillic mucilage plugs to avoid such low xylem water potentials? Active water transport through xylem mucilage linings? xylem water potential ca. -3 Mpa? root water potential ca. - 2.7 Mpa? salt water ca. -2.5 MPa
Alternative water uptake according to cohesion theory: dry air ca. -90 Mpa leaf water potential ca. -3.5 Mpa alternative theory: water uptake through hygrophillic mucilage plugs but: water in meta-stable to avoid status such when low xylem under water -3 Mpa potentials?! Active water transport through xylem mucilage linings? xylem water potential ca. -3 Mpa? root water potential ca. - 2.7 Mpa? salt water ca. -2.5 MPa
Freshwater is abundant in the atmosphere at night
Freshwater is abundant in the atmosphere at night So why not make use of it?
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 CO2 NSCs NSCs NSCs
Stem diameter Time
Stem diameter Stem growth + NSC? Time
Stem diameter Stem stasis + NSC Time
Stem diameter What s happening here? Time
Stem diameter And what s happening here? Time
Some early data
Inverse of turgor
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
AND More mud!
Thanks
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