Wednesday, May 02, 2007

The carbon-nitrogen cycle systems self organizing away from equilibrium

The Third Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) predicts that the Ca increase alone could stimulate terrestrial carbon (C) sequestration by 350–980 Gt (1 Gt " 1 # 1015 g) C in the 21st Century (Houghton et al. 2001).Sequestering 350–980 Gt C in terrestrial ecosystems requires 7.7–37.5 Gt of nitrogen (N) according to the calculation made by Hungate et al. (2003)

An interesting introduction in Luo et al Ecology, 87(1), 2006, pp. 53–63 a Meta analysis showing the requirements for AGW co2 sequestration and its requirements from the N cycle.

As is known the cycles tend to overlap in increases and decreases due to biogeochemical functions .An analogy is two dancers each listening to music at different tempos ,where corrections can be observed as stumbles etc as they correct and over correct in a state of self organization.

The close coupling between C and N cycles during ecosystem development over the earth history (Vitousek 2004 Nutrient cycling and limitation) and under elevated CO2 suggests that C and N processes are mutually regulated by each other. Although the past research in the CO2 research community has focused on regulation of C processes by soil N availability, regulation of N fixation and loss processes by C input under elevated CO2 is indeed an equally important issue in global change ecology that has to be carefully examined. The close coupling between C and N cycles also must be considered when we predict C sequestration in future global change scenarios.

Whist there are other important nutrient ratios that alter parameters this is a good comparative analysis.

Abstract. The capability of terrestrial ecosystems to sequester carbon (C) plays a critical role in regulating future climatic change yet depends on nitrogen (N) availability. To predict long-term ecosystem C storage, it is essential to examine whether soil N becomes progressively limiting as C and N are sequestered in long-lived plant biomass and soil organic matter. A critical parameter to indicate the long-term progressive N limitation (PNL)is net change in ecosystem N content in association with C accumulation in plant and soil pools under elevated CO2. We compiled data from 104 published papers that study C and N dynamics at ambient and elevated CO2. The compiled database contains C contents, N contents, and C:N ratio in various plant and soil pools, and root:shoot ratio. Averaged C and N pool sizes in plant and soil all significantly increase at elevated CO2 in comparison to those at ambient CO2, ranging from a 5% increase in shoot N content to a 32% increase in root C content. The C and N contents in litter pools are consistently higher in elevated than ambient CO2 among all the surveyed studies whereas C and N contents in the other pools increase in some studies and decrease in other studies. The high variability in CO2- induced changes in C and N pool sizes results from diverse responses of various C and N processes to elevated CO2. Averaged C:N ratios are higher by 3% in litter and soil pools and 11% in root and shoot pools at elevated relative to ambient CO2. Elevated CO2 slightly increases root:shoot ratio. The net N accumulation in plant and soil pools at least helps prevent complete down-regulation of, and likely supports, long-term CO2 stimulation of C sequestration. The concomitant C and N accumulations in response to rising atmospheric CO2 may reflect intrinsic nature of ecosystem development as revealed before by studies of succession over hundreds to millions of years.


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