Mitteilungen der Gesellschaft für Pflanzenbauwissenschaften Band 23

Mitt. Ges. Pflanzenbauwiss. 23: 61–62 (2011)
Comparative analysis of spatio-temporal patterns of carbon and
water fluxes in production fields of winter wheat and sugar beet
Moritz Kupisch 1 , Matthias Langensiepen 1 , Mark van Wijk 2 , Anja Stadler 1 and
Frank Ewert 1
1 Crop Science Group, Institute of Crop Science and Resource Protection, Faculty of Agriculture, University
of Bonn; 2 Plant Production Systems Group, Wageningen University. E-Mail: mkupisch@unibonn.de
Introduction
Assimilation and transpiration are important processes affecting crop growth and
yield. Modelling growth and water transport at the field scale should therefore
consider the spatio-temporal variability of these processes.
Up-scaling gas-exchange from leaf to field is a particular challenge, because
heterogeneities in soil and microclimate invoke distinctive regulation mechanisms
that become apparent at the canopy level causing heterogeneities in gas fluxes. The
purpose of this study was to analyze gas exchange at the point scale in a winterwheat
and sugar beet crop, both at leaf and canopy levels, and to use spatial
integration to characterize assimilation and transpiration at the field level.
Material and Methods
Measurements were carried out between May and October 2010 near Selhausen
(50.868° N, 6.451° E), located in the Rur-catchment of North-Rhine-Westphalia. The
wheat and sugar beet fields have each a gradient of two meters in the direction SE –
NW, with sandy loam in the upper part and clayey silt in the lower part. Three
measuring locations were chosen in each field which represent ranges including the
extremes of soil properties and topography. Transpiration and CO2-assimilation were
measured alternately at leaf and canopy level with a LI-6400 XT gas exchange
analyzer (Licor Biosciences). Leaf-level measurements were carried out in the
regular open path chamber cuvette mode. Canopy gas-exchange was measured with
a closed Plexiglas chamber on a 1 × 1 m ground area with height adapters and using
a custom protocol to monitor concentration changes with the sample IRGA at one
second intervals. Gas-exchange was derived by fitting quadratic and saturation
functions to measured trends in gas concentration changes of CO2 and H2O,
respectively, and taking the slope of these functions at t=0 seconds for calculating
flux rates. Determination of leaf area index was conducted by using a PARceptometer
(AccuPAR LP-80). Carbon and nitrogen contents of sunlit and shaded
leaves were also measured.
Results and Discussion
Temporal and spatial variabilities were small for leaf photosynthesis and transpiration
in both crops. Distinct daily patterns were not observed, except during severe hot and
dry days when rates declined in the afternoon. Leaf nitrogen content in wheat was
equal at all locations until the end of flowering, ranging from 4 to 5%. Increasing
differences in leaf nitrogen between stressed (1%) and unstressed (3%) plants were
observed towards the end of the season. In beet leaves, the differences in the field
were higher at the beginning (values between 3 and 5%) but decreased until the end
(all around 5%).