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| Titel |
Modelling C allocation in response to nutrient availability |
| VerfasserIn |
Benjamin Stocker, Colin Prentice |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250109840
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| Publikation (Nr.) |
 EGU/EGU2015-9788.pdf |
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| Zusammenfassung |
| Carbon (C) allocation in ecosystems is a key variable of the global terrestrial C cycle. While
photosynthesis governs the amount of C that enters ecosystems, its subsequent allocation to
compartments with different life times determines its over-all residence time and variations
in allocation patterns drive changes in ecosystem C balance and its response to
environmental change. A better understanding of the controls on allocation is thus key to
improving global vegetation models that commonly rely on using fixed partitioning
factors.
Observational data suggests variations of ecosystem structure and functioning along
large-scale gradients of resource availability. Below-ground C allocation, inferred as gross
primary production minus above-ground biomass production increases along gradients of
decreasing nutrient availability. This is not only due to more root growth, but also due to
enhanced production of exudates and stimulation of root symbionts and has been
interpreted to reflect optimal plant allocation decisions under a varying soil fertility
status.
Here, we propose a model that accounts for trade-offs between (i) growth in above-ground
and (ii) below-ground plant compartments, (iii) exudation to the rhizosphere and root
symbionts and (iv) temporary storage in non-structural pools. By postulating the
maximization of long-term growth under a given (seasonal regime) of soil nitrogen (N)
availability, we attempt to reproduce observed large-scale gradients.
The model is formulated based on a C cost for different N uptake decisions, where the cost is
a function of N availability, root mass, and soil temperature (for biological N fixation). On a
daily time scale, ecosystem N uptake may be realized by C exudation to the rhizosphere
and/or symbiotic fixation of atmospheric N2. On an annual time scale, allocation to roots
versus leaves is adjusted to soil inorganic N availability and modeled to yield maximum total
growth. Exudation versus temporary storage of C is modeled to balance seasonal and annual
variations in N availability and demand and yield a minimum multi-annual cost of N
uptake.
We present first results where the model is applied along a gradient of N availability.
Predictions are tested against a data set of total below-ground allocation and C use efficiency
across global scales. Opportunities and limitations of such an implementation in global
vegetation models are discussed. |
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