Constraining Simulated Respiration Fluxes with Component Measurements in
a Dry Eucalypt Forest
Abstract
Isolating significant signals from temporal variations in autotrophic
and heterotrophic components of ecosystem respiration (Reco) is required
to better quantify the temperature sensitivity of the land carbon cycle
processes. Here we present diurnal and seasonal patterns in field and
model-based components of respiration and investigate their responses to
environmental conditions at a dry eucalypt forest, the Cumberland Plain
SuperSite of the Australian Terrestrial Ecosystem Research Network. We
conducted measurement campaigns of total CO2 flux from the soil surface
(Rsoil), soil microbial respiration (Rmicrobe), root respiration
(Rroot), litter respiration (Rlitter), and stem respiration (Rstem) in
2018. In total, six infrared gas analyzers with closed, dynamic
auto-chambers and six forced diffusion auto-chambers were used for
periodic campaigns. Further, Reco and its components were simulated
using the Community Atmosphere-Biosphere Land Exchange model (CABLE),
constrained by eddy covariance measurements and chamber measurements of
Rsoil. A new version of CABLE was implemented with the Dual Arrhenius
Michaelis Menten (DAMM) formulation to assess the importance of
substrate availability for simulating Rmicrobe. We found that
respiration rates showed similar diurnal patterns among the components,
showing diurnal hysteresis between respiration components and
temperature. In this dry ecosystem, the respiratory components were more
responsive to seasonally increasing temperature in wet than in dry
periods, and the responses were dependent on atmospheric relative
humidity affecting the litter layer moisture content. The temperature
sensitivity was significantly higher in Rstem than in other components.
Based on observed fluxes of Rmicrobe in trenched plots and Rsoil in
intact soil plots, the mean contribution of Rroot to Rsoil was less than
20 % for the dry seasons, while mean Rstem was two times greater than
mean Rsoil suggesting that Rstem should be not overlooked in ecosystem
flux estimations. This study highlights that partitioning the
respiratory components and accounting for their different
temperature-responses will be necessary to reduce uncertainty in
modelling carbon-climate feedbacks.