Mitteilungen der Gesellschaft für Pflanzenbauwissenschaften Band 23

Mitt. Ges. Pflanzenbauwiss. 23: 108–109 (2011)
Application of closed-chamber measurements for screening
canopy gas-exchange
Matthias Langensiepen 1 , Moritz Kupisch 1 , Anja Stadler 1 , Mark van Wijk 2 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, Wageningen,
Netherlands. E-Mail: mlang@uni-bonn.de
Introduction
Closed canopy chambers are still the only practical solution for rapid screening of
gas-exchange in larger cropped areas with many sample points. Widely accepted
measuring equipment is not available on the market and standard protocols missing.
Chamber designs, measuring principles and data interpretations thus vary greatly
among reported studies. Chamber performances must be tested in each individual
case to provide confidence in calculated results. Physical characteristics of a mobile
chamber construction were determined in this study, the most suitable flux
calculation methods identified, and trends in concentration changes compared
against independent measurements of sap-flow in wheat. We emphasize on the
determination of vapor flux as it is more difficult to determine than CO2 flux due to the
larger effect of altered physical transport conditions on stomatal regulation.
Material and Methods
The study was conducted in a spring-wheat plot maintained at the agricultural
experimental station of the University of Bonn at Klein-Altendorf. The plot was managed
according to standard agronomic practice.
The chamber was constructed with Plexiglas and had a dimension of 1x1x0.3 m 3 .
Height-adapters built from the same material were used to interface the chamber with
a frame that was placed into the soil for ceiling the entire construction from ambient
air. Fans were placed in each corner to turn over the chamber air with a rate of 111
m 3 /h per fan. Changes in vapor and carbon-dioxide concentrations were measured
with the sample cell of a LI 6400 XT portable photosynthesis system at 1 second
intervals until vapor started to condense at the chamber walls.
Sap flow was measured with the Dynamax heat-balance technique in randomly
selected wheat tillers inside the gas-flux measuring area. The sensors were attached
to plastic sticks stuck into the ground for preventing stalk bending and thoroughly
shielded against ambient conditions with foam enclosures, plastic- and aluminum
foils. The measuring interval was set to the lowest possible value of 1 minute.
Intermediate values were calculated by spline-interpolation.
Measurements were carried out in 2010 under clear summer sky conditions
between 10am and 2pm on 5 days during ear emergence to prevent effects from
transient regulation of canopy gas-exchange and to make experimental results
comparable.
Results and Discussion
Results of this study are summarized in Fig. 1 which shows the difference between
average sap-flow and vapor concentration rate changes during chamber placement.
Scatter during the first 50 seconds is large compared to the remaining period and
results from mixing lags and plant acclimatization to altered transport conditions.