Agriculture Reference
In-Depth Information
Keywords FACE (free air carbon dioxide enrichment) • Carbon dioxide • Climate
change • NUE (nitrogen use efficiency) • Metabolism • Nitrogen • Photosynthesis
• Nutrient content • Roots • Soils
Introduction
Carbon exchange between large reservoirs in the atmosphere, land and oceans
constitutes the complex global carbon cycle. The carbon involved in this cycle is
in a state of dynamic equilibrium, with as much as 400 gigatonnes of carbon
exchanged each year (Kitchen
2014
). Since the industrial revolution in the nine-
teenth century, emission of anthropogenic greenhouse gases, predominantly in the
form of carbon dioxide, has disturbed this equilibrium (Kitchen
2014
). In 2012,
human activities caused the release of more than 10 gigatonnes additional carbon
emissions into the atmosphere, a number that has grown from the past and will grow
with future global economic development.
Surpluses of released carbon have led to the increase in atmospheric CO
2
concen-
trations [CO
2
] from a pre-industrial concentration of ~278
mol mol
1
to a current
μ
mol mol
1
. Atmospheric [CO
2
] is predicted to reach
concentration of ~395
μ
mol mol
1
by 2050 according to the IPCC scenario A1B (Carter et al.
2007
).
This would mean that every terrestrial plant will be exposed to at least a 40 % greater
concentration in one of the key resources for plant growth compared to present
conditions. Effects on climate aside, such a large change, especially if it is not matched
by similar changes in other plant nutrients, will also have considerable effects on plant
production (Ziska
2008
). Arguably therefore any crop improvement efforts must
account for the direct effects of increasing atmospheric [CO
2
] on plant metabolism
and crop growth (Ainsworth et al.
2008
; Hatfield et al.
2011
; Tausz et al.
2013
).
Since the 1980s, significant research efforts have been undertaken to understand
how plants will perform and grow under atmospheric [CO
2
] enrichment. Method-
ological approaches range from controlled environments such as laboratory growth
chambers and glasshouses to closed-top and open-top field chambers and Free Air
Carbon dioxide Enrichment (FACE) systems. Early enclosure experiments mark
the basic knowledge of our understanding of plant responses to CO
2
enrichment but
they also include potential limitations. For example, results from enclosure exper-
iments may include “chamber effects”, possibly exaggerating the effects of ele-
vated [CO
2
]. Enclosure studies also often include changed radiation conditions,
greater than normal growing temperatures, changed microclimate factors such as
wind speed or relative humidity and/or restricted root growth due to the use of pots
or containers (Ainsworth and Long
2005
; Amthor
2001
). In contrast, FACE sys-
tems allow the effects of CO
2
enrichment on plant metabolism and growth to be
studied under natural and fully open air conditions. Although some concerns have
been raised about the rapid fluctuations of [CO
2
] in FACE systems (Bunce
2012
),
advantages such as the ability to grow crops in their natural microclimate probably
outweigh any such disadvantages. FACE systems might also produce misleading
data if they are used in climates and soils atypical for the plants investigated,
~550
μ
