Water uptake patterns in a tropical rainforest ecosystem and consequences on intra- and inter-annual variations in C flux and balance

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Water uptake patterns in tropical rainforest ecosystem

and consequences on intra- and inter-annual variations

in C flux and balance

Bonal D.

w/ Aguilos M., Burban B., Hérault B., Verbeeck H., De

Deurwaerder H., Ziegler C., Coste S., Stahl C.


Beer et al. 2010


• Tropical rainforests are the terrestrial ecosystems with the strongest GPP values.

• In the context of climate change, a precise knowledge of C fluxes and balance in

these regions is important to simulate and predict its impact on vegetation

dynamics and global C budget.




• Annual cycle of normalized gross ecosystem productivity, GEP GEPmax-1

• Normalized Photosynthetic Capacity, Pc Pcmax-1

• Daytime photosynthetic active radiation, PAR (mol m−2 s−1)

• Top of the atmosphere (TOA) incoming solar radiation in the middle panels.


Drivers of variations in carbon flux and balance

• Gross Primary productivity (GPP) • Respiration of Ecosystem (RE) • Net Ecosystem Exchange (NEE)

• Solar radiation is the main driver of C fluxes and balance

• Under no water limitation conditions:

Leaf flush and litterfall are strong drivers of GPP (

Restrepo-Coupe et al. 2013


• At sites with seasonal drought:


Ecosystem scale

What about individual tree-scale response

to drought and soil water extraction depth

by tropical plants?

Functional ecology studies since decades to

understand drought response of canopy trees


Bonal et al. 2016 Synthesis

What about root development strategies?

Trees display different strategies to resist or adapt to drought stress



Nepstad et al. 1994

Deep roots in tropical forest


Soil δ


H (‰)

Schematic vertical distribution of roots


One word about the stable isotope approach (Labelling experiment)

Xylem water δ


H (‰)

+600 ‰

-50 ‰

+100 ‰

e.g.: Romero-Saltos et al. 2005 Stahl et al. 2013 Grossiord et al. 2014


Percentage of the number of trees in the different classes of mean depth of soil water uptake at 2 dates (1 week difference) during the dry season.

Stahl et al. 2013 Mean depths of water uptake (µ) by Coussarea racemosa, Sclerolobium

chrysophyllum, and Eschweilera pedicellata trees (deuterium approach). The

number below each column is the number of trees (of five in each species) Romero-Saltos et al. 2005

46% of the studied trees

extract most of their water

from below 100 cm depth !

65 trees : diameters = 1.3–79.9 cm / heights = 2.0–38.0 m. 47 different species

No clear relationship between tree

size and water uptake depth

Water uptake depth during dry periods?


De Deurwaerder et al. 2018

Statistical differences are indicated by different letters

(Non-parametric Kruskal-Wallis test with Dunn post hoc analyses, p < 0.05)

• Does not support liana deep root strategy -> rather shallow water acquisition

• Niche partitioning during dry season among deep rooted trees and lianas

• Shallow rooting allows fast capture of dry season precipitation

What about lianas?

• Abundance of lianas increased in the last three decades in Neotropical forest ecosystems (e.g. Schnitzer & Bongers, 2011)

• High liana abundance causes elevated tree mortality and reduced tree growth due to an increase in competition for light, nutrients and water (Ingwell et al., 2010; van der Heijden et al., 2015)

• Lianas therefore play a key role in current tropical forest dynamics and functioning

33 Lianas

38 Trees


Interspecific variability of drought response strategies and adaptive

mechanisms of tropical forest trees and lianas are poorly represented in

ecosystem models

How can we improve this?

Adapt existing models?

Develop new models?

Major challenge !

=> Will allow improving simulations of tropical forest responses to climatic

variations, predicting vegetation dynamics, and mitigating the impacts of

climate change on vegetation