Abstract
Understanding rhizosphere processes in relation to increasing atmospheric CO(2) concentrations is important for predicting the response of forest ecosystems to environmental changes, because rhizosphere processes are intimately linked with nutrient cycling and soil organic matter decomposition, both of which feedback to tree growth and soil carbon storage. Plants grown in elevated CO(2) substantially increase C input to the rhizosphere. Although it is known that elevated CO(2) enhances rhizosphere respiration more than it enhances root biomass, the fate and function of this extra carbon input to the rhizosphere in response to elevated CO(2) are not clear. Depending on specific plant and soil conditions, the increased carbon input to the rhizosphere can result in an increase, a decrease, or no effect on soil organic matter decomposition and nutrient mineralization. Three mechanisms may account for these inconsistent results: (1) the "preferential substrate utilization" hypothesis; (2) the "priming effect" hypothesis; and (3) the "competition" hypothesis, i.e., competition for mineral nutrients between plants and soil microorganisms. A microbial growth model is developed that quantitatively links the increased rhizosphere input in response to elevated CO(2) with soil organic matter decomposition. The model incorporates the three proposed mechanisms, and simulates the complexity of the rhizosphere processes. The model also illustrates mechanistically the interactions among nitrogen availability, substrate quality, and microbial dynamics when the system is exposed to elevated CO(2).
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Claims 5
Claim · model-written summary
Plants grown under elevated CO2 substantially increase rhizosphere carbon input.
- Taxon
- PlantsViridiplantaee0
- Treatment
- elevated CO(2)e0
- Outcome
- C input to the rhizospheree0
- Direction
- increasee0
Not reportedComparator
Verbatim
e0“Plants grown in elevated CO(2) substantially increase C input to the rhizosphere”
Claim · model-written summary
Elevated CO2 enhances rhizosphere respiration more than root biomass.
- Treatment
- elevated CO(2)e0
- Outcome
- rhizosphere respiratione0
- Direction
- enhancese0
- Comparator
- root biomasse0
Not reportedTaxon
Verbatim
e0“elevated CO(2) enhances rhizosphere respiration more than it enhances root biomass”
t0“Rhizosphere feedbacks”
Claim · model-written summary
Depending on conditions, increased rhizosphere carbon input can increase, decrease or leave unchanged organic matter decomposition and nutrient mineralization.
- Taxon
- plante0
- Outcome
- soil organic matter decomposition and nutrient mineralizatione0
- Qualifier
- Depending on specific plant and soil conditionse0
Not reportedDirection
Verbatim
e0“Depending on specific plant and soil conditions, the increased carbon input to the rhizosphere can result in an increase, a decrease, or no effect on soil organic matter decomposition and nutrient mineralization”
Claim · model-written summary
A microbial growth model quantitatively links increased rhizosphere input under elevated CO2 with soil organic matter decomposition.
- Treatment
- elevated CO(2)e0
- Outcome
- soil organic matter decompositione0
- Comparator
- increased rhizosphere inpute0
Not reportedTaxonValue
Verbatim
e0“A microbial growth model is developed that quantitatively links the increased rhizosphere input in response to elevated CO(2) with soil organic matter decomposition”
Claim · model-written summary
The model illustrates interactions among nitrogen availability, substrate quality and microbial dynamics under elevated CO2.
- Outcome
- interactions among nitrogen availability, substrate quality, and microbial dynamicse0
Not reportedComparatorValue
Verbatim
e0“The model also illustrates mechanistically the interactions among nitrogen availability, substrate quality, and microbial dynamics when the system is exposed to elevated CO(2)”