How does soil moisture and fertility affect belowground

1
How does soil moisture and fertility affect
below-ground carbon allocation and cycling?
Daniel Metcalfe1, Luiz Aragão2 Samuel
Almeida3 1University of Edinburgh,
U.K. 2University of Oxford, U.K. 3Museu Paraense
Emilio Goeldi Correspondence d.b.metcalfe_at_sms.ed.
ac.uk
Background There is an urgent need to understand
in greater detail the interactions between soil
characteristics and ecosystem processes.
Experimental throughfall exclusion at Caxiuanã,
E. Amazonia has caused a significant decrease in
soil respiration and a shift in above-ground
productivity. Soil fertility may also have an
important effect upon productivity (Malhi et al.
2004). However, without data on below-ground C
dynamics, any representation of the
ecosystem-level response to environmental
influences remains incomplete.
Data available at Caxiuanã
Hypotheses Experiment The pattern of carbon
allocation and cycling above and below-ground is
a key uncertainty in climate models (Dufresne et
al. 2002). Above-ground NPP varies by a factor of
three across the Amazon basin (Malhi et al.
2004). The underlying mechanisms responsible for
this variation are unclear. This study will
address the following science questions 1) What
is the effect of soil moisture and fertility upon
NPP? 2) What is the effect of soil moisture and
fertility upon the proportion of NPP allocated to
different ecosystem components? Below-ground C
stocks and fluxes at sites in Caxiuanã, with
different levels of soil fertility and moisture,
will be compared to control sites. An additional
site will be established in Tambopata, Peru.
Information will be integrated with existing
datasets.
ecosystem respiration
GPP
above-ground NPP
litterfall
soil respiration
? ? ? ? ? ? ?

• Objectives
• 1) Quantify effect of soil moisture fertility
  upon root growth, turnover and longevity.
• 2) Convert data on root growth dynamics to
  nutrient fluxes.
• 3) Combine results with existing above-ground
  data to generate an improved model of C
  cycling at the site.

Equipment Methods
Rhizotrons Record root appearance, growth and
disappearance every 14 days with tracings and
digital images.
Ingrowth cores Record live root biomass every
three months (dry season, wet season, wet-dry
dry-wet transition).
Chemical analysis Measure C N content per unit
biomass of live root.
Analysis Integration
Root survival model Quantify the effect of
different root characteristics and environmental
variables upon root longevity.
Biomass conversion Convert root appearance
disappearance to C N flux into, and out of,
roots.
Output Modelling
Input data into existing plant physiology model
(SPA), use data assimilation approach to produce
an improved estimate of ecosystem C cycling and
allocation
References 1) Dufresne, J. L. et al. (2002) On
the magnitude of positive feedback between future
climate change and the carbon cycle. Geophysical
Research Letters 29 1-4. 2) Malhi, Y. et al.
(2004). The above-ground coarse wood productivity
of 104 Neotropical forest plots. Global change
Biology 10 563-591.