『Abstract
Phosphorus (P) is a crucial element for life and therefore for
maintaining ecosystem productivity. Its local availability to
the terrestrial biosphere results from the interaction between
climate, tectonic uplift, atmospheric transport and biotic cycling.
Here we present a mathematical model that describes the terrestrial
P-cycle in a simple but comprehensive way. The resulting dynamical
system can be solved analytically for steady-state conditions,
allowing us to test the sensitivity of the P-availability to the
key parameters and processes. Given constant inputs, we find that
humid ecosystems exhibit lower P availability due to higher runoff
and losses, and that tectonic uplift is a fundamental constraint.
In particular, we find that in humid ecosystems the biotic cycling
seem essential to maintain long-term P-availability. The time-dependent
P dynamics for the Franz Josef and Hawaii chronosequences show
how tectonic uplift is an important constraint on ecosystem productivity,
while hydroclimatic conditions control the P-losses and speed
towards steady-state. The model also helps describe how with limited
uplift and atmospheric input, as in the case of the Amazon Basin,
ecosystems must rely on mechanisms that enhance P-availability
and retention. Our analysis underlines the need to include the
P cycle in global vegetation-atmosphere models for a reliable
representation of the response of the terrestrial biosphere to
global change.』
1. Motivation
2. Model formulation
2.1. Synthesis of the P-cycle model
2.2. Climatic forcing
2.3. Inputs
2.3.1. Atmospheric transport and input from animals
2.3.2. Input by tectonic and isostatic uplift
2.4. Ecosystem internal fluxes
2.4.1. Phosphorus weathering
2.4.2. Formation of secondary minerals and P occlusion
2.4.3. Vegetation P-uptake and litter fall
2.4.4. P-mineralization
2.5. Losses
2.6. P-balance equations
3. Results
3.1. Steady-state solution
3.1.1. Sensitivity of ecosystems external inputs to soil moisture
3.1.2. Sensitivity of organic biomass losses to soil moisture
3.1.3. Sensitivity of active P uptake by vegetation to soil
moisture
3.1.4. Special solutions for systems without uplift
3.2. Phosphorus temporal dynamics
3.2.1. The Walker and Syers' model for New Zealand
3.2.2. The Hawaii chronosequence
3.2.3. Dynamics of an uplift dominated site (the Amazon Basin)
4. Summary and conclusions
Acknowledgements
References