In:
Biogeosciences, Copernicus GmbH, Vol. 17, No. 17 ( 2020-08-31), p. 4375-4404
Kurzfassung:
Abstract. The CloudRoots field experiment was designed to obtain a
comprehensive observational dataset that includes soil, plant, and
atmospheric variables to investigate the interaction between a heterogeneous
land surface and its overlying atmospheric boundary layer at the sub-hourly
and sub-kilometre scale. Our findings demonstrate the need to include
measurements at leaf level to better understand the relations between
stomatal aperture and evapotranspiration (ET) during the growing season at
the diurnal scale. Based on these observations, we obtain accurate
parameters for the mechanistic representation of photosynthesis and stomatal
aperture. Once the new parameters are implemented, the model reproduces the
stomatal leaf conductance and the leaf-level photosynthesis satisfactorily.
At the canopy scale, we find a consistent diurnal pattern on the
contributions of plant transpiration and soil evaporation using different
measurement techniques. From highly resolved vertical profile measurements of carbon dioxide (CO2) and other state variables, we infer a
profile of the CO2 assimilation in the canopy with non-linear
variations with height. Observations taken with a laser scintillometer allow
us to quantify the non-steadiness of the surface turbulent fluxes during the
rapid changes driven by perturbation of photosynthetically active radiation
by cloud flecks. More specifically, we find 2 min delays between the
cloud radiation perturbation and ET. To study the relevance of advection and
surface heterogeneity for the land–atmosphere interaction, we employ a
coupled surface–atmospheric conceptual model that integrates the surface and
upper-air observations made at different scales from leaf to the landscape.
At the landscape scale, we calculate a composite sensible heat flux by
weighting measured fluxes with two different land use categories, which is
consistent with the diurnal evolution of the boundary layer depth. Using
sun-induced fluorescence measurements, we also quantify the spatial
variability of ET and find large variations at the sub-kilometre scale
around the CloudRoots site. Our study shows that throughout the entire
growing season, the wide variations in stomatal opening and photosynthesis
lead to large diurnal variations of plant transpiration at the leaf, plant,
canopy, and landscape scales. Integrating different advanced instrumental
techniques with modelling also enables us to determine variations of ET that
depend on the scale where the measurement were taken and on the plant
growing stage.
Materialart:
Online-Ressource
ISSN:
1726-4189
DOI:
10.5194/bg-17-4375-2020
DOI:
10.5194/bg-17-4375-2020-supplement
Sprache:
Englisch
Verlag:
Copernicus GmbH
Publikationsdatum:
2020
ZDB Id:
2158181-2
