Flux-Variance Similarity Partitioning: Accounting for Carbon-Water Dissimilarity During Photodegradation of a Climactically Dynamic Semi-Arid Grassland
Abstract
In eddy covariance measurements, a consistent and reliable method for partitioning net carbon fluxes and total water fluxes is critical. This is because we need information on the processes which contribute to these colligative fluxes: photosynthesis, respiration, abiotic decomposition, transpiration, and evaporation which occurs outside of leaves (e.g., soil surfaces, intercepted rainfall, open water). FLUXNET has progressed the global standardisation of consistently partitioned carbon fluxes, but there remain some locations where the application of standard partitioning methods can generate spurious results (e.g., a photosynthetic carbon sink in the atmosphere). Hummock grasslands cover vast portions of the Australian interior, where their large fluctuations in carbon budget can have global implications. Abiotic decomposition as a result of photodegradation (i.e., full spectrum sunlight-mediated breakdown of lignin in leaf litter) can be a major source of carbon to the atmosphere in these ecosystems. In this study, we used flux-variance similarity theory to inform the partitioning of photodegradation, ecosystem respiration and gross primary production, finding that the strong contribution of abiotic decomposition in the hummock grassland violated CO2-H20 similarity despite 97% energy balance closure (i.e., strong H2O-temperature similarity). This result was the consequence of a weakening of the correlation between atmospheric carbon and water densities, given their measured variability. However, a range of nominal CO2 fluxes was found to exist for which flux-variance theory approximately applies, from which an estimate of photodegradation was inferred using the two-equation, global root finder method of Palatella et al. (2014, Bound.-Lay. Meteor. 153: 327-337). Photodegradation and photosynthesis followed similar responses to light, emphasising the strong correlation between carbon source and sink behaviour of semi-arid central Australia. Thus, carbon source strength across a large area of the Australian continent is primarily constrained by biomass accumulation during exceptionally wet periods. By estimating photodegradation in situ for the first time, this study provides an important first step for closing the carbon budget of a drier world.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.B21C..08C
- Keywords:
-
- 3355 Regional modeling;
- ATMOSPHERIC PROCESSES;
- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCES;
- 0426 Biosphere/atmosphere interactions;
- BIOGEOSCIENCES;
- 0430 Computational methods and data processing;
- BIOGEOSCIENCES