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
Context
• 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.
Context
• 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
2015
Nepstad et al. 1994
Deep roots in tropical forest
Soil δ
2H (‰)
Schematic vertical distribution of roots
9
One word about the stable isotope approach (Labelling experiment)
Xylem water δ
2H (‰)
+600 ‰
-50 ‰
+100 ‰
e.g.: Romero-Saltos et al. 2005 Stahl et al. 2013 Grossiord et al. 2014Percentage 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
