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Free Air Concentration Enrichment Facility (FACE)
By: Dr. Vivek Pandey*
The anticipated increases in global atmospheric CO2
concentrations have led to much research that aims to determine the growth
of plants when exposed to the levels of CO2 predicted for the
latter part of this century. The free air CO2 enrichment (FACE)
technique has been successfully used to grow a wide variety of vegetation
types under elevated CO2 for example wheat, pastures and trees.
Compared with methods that grow plants under elevated CO2 in enclosures,
the main advantage of FACE is that it does not substantially modify
environmental factors such as incident solar radiation, temperature,
humidity and wind, which can influence the response to elevated CO2. Generally, FACE systems enrich a circular area of vegetation
with CO2 in order to generate a zone with a higher CO2 than that of the surrounding ambient atmosphere. The CO2 is usually emitted from a structure (commonly referred to as a
ring) constructed from pipes or tubes that surrounds the vegetation and is
dispersed across the vegetation by the wind.
Fig 1. FACE system at NBRI garden. A: FACE rings and B- control room.
The NBRI FACE facility consists of three hexagonal CO2 enrichment rings
together with their three companion ambient (non-enrichment) rings (Fig 1
A). The ring has a diameter of 10 m. Each FACE ring is made up of six 3 m
long G.I. pipes. Each horizontal tube is grounded in soil. Each horizontal
arm is fitted, at three points, with 5 m vertical pipes. These vertical
pipes have nozzles to release CO2 inside the ring. CO2 is supplied through
30 kg cylinders fitted with pre-heaters. 300 litre capacity of air
compressor (3 nos.) are used to pump air mixed with CO2 into FACE ring
through GI pipes. Six solenoid valves are used for each arm of FACE ring
and one valve is for main CO2 line, therefore total seven solenoid valve
used to control CO2 release inside the ring. The CO2 concentration inside
the ring is sampled at 3 places and fed to the infra red gas analyzer.
Before being fed to the analyzer, air is passed through a desiccant and
filter to remove moisture and particulate matter, respectively. In the
middle of the ring sensors for wind speed and direction, temperature,
humidity, light intensity and CO2 are mounted. Signals from these sensors
are transmitted toward control room through four core shielded cable. Fully
automatic control system (SCADA) for monitoring and regulation of desired
CO2 works with inputs form the CO2 analyzer, temperature and anemometer
(Fig1B). The control system is operated with microprocessor through
in-built timer and data logger input. On line display of temperature,
humidity, CO2 concentration in ppm and air velocity is integrated with
necessary controls and monitoring station controller. The systems have
memory backup and real time clock combination and single window operation
to monitor temperature, humidity, CO2 level and air velocity
with direction.
In one of the experiments at NBRI, wheat plants were grown in Free Air
Concentration Enrichment (FACE) rings. Three rings were supplied with
elevated CO2 while other 3 rings served as control (supplied with air). CO2
enrichment was started after seed germination and continued until final
harvest. The targeted CO2 concentration was reached to about 470 ppm.
Higher photosynthetic rate (A) rate was observed at vegetative stage than
at flowering stage and A was more in eCO2 at both the stages. Similar
responses were found in stomatal conductance. A/Ci curve indicated that
photosynthetic acclimation was almost similar at both the stages in both
the treatments. Increased shoot biomass was found in plants grown under
eCO2. All the yield parameters also showed upward trend under eCO2,
including grain wt/plant, 1000 grain wt and Harvest Index. The average
yield of Kundan variety has been reported to be 40-45 Q/hectare. We found
that in control plants, estimated yield was 44.48 Q/hectare while in eCO2 it was 56.3 Q/hectare.
Wheat grain proteomics showed that out of 49 differentially expressed
proteins, 24 were up-regulated and 25 were down-regulated in grains under
eCO2 condition. Through mass spectrometry 33 proteins were identified and
functionally characterized. They were found to be involved mainly in carbon
metabolism, storage, defence and proteolysis. Gluten proteins are normally
associated with superior end quality, especially dough strength and
elasticity. There was more expression of high molecular wt glutenin and LMW
glutenin proteins in eCO2 wheat grains. Differences in glutenin
ratio in wheat seeds might have an adverse impact on bread dough
end-product quality. Further studies are going on with more wheat
varieties.
*Plant Physiology Laboratory, CSIR-NBRI, Rana Pratap Marg, Lucknow-226001,
India. E-mail: [email protected]
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