Agriculture Reference
In-Depth Information
group. Furthermore, the early yield after transplanting to the field was improved
(Fierro et al.
1994
). Some more examples of benefits for other vegetable crops are
compendiously presented by Gruda (
2005
).
Carbon dioxide enrichment could have a positive effect on plant propagation and
promoting the rooting of cuttings. Even at low irradiance growth promotion can be
achieved by CO
2
enrichment, due to inhibition of photorespiration and the associ-
ated reduction of the light compensation point. This is of great benefit in winter/
spring period in higher latitudes when light levels are low. The negative effects
of low light conditions (Fierro et al.
1994
), low temperatures (Frantz
2011
), high
salinity levels in irrigation water available in Mediterranean countries (Romero-
Aranda et al.
2002
) or high electric conductivity (EC) levels of nutrient solutions
(Li et al.
1999
) can be diminished by CO
2
enrichment. Supplementary CO
2
boosted
total leaf number and mass of lettuce even though temperatures were maintained at
1.67 °C (3 F) lower than in a traditionally well insulated greenhouse without added
CO
2
at a commercial facility (Frantz
2011
).
There is less information on the effect of CO
2
concentration as an elicitor on the
internal quality of vegetables with most publications reporting no effect on product
quality (Gruda
2005
). However, there is evidence that the enhanced rate of photo-
synthesis observed during short-term exposure to high CO
2
may not be sustained
over long periods (Drake et al.
1997
; Frantz and Ling
2011
). Besford et al. (
1990
)
summarized that growth for a number of weeks in high CO
2
, involving several
vegetable crops and tobacco did not maintain the photosynthetic gain, when plants
were measured at normal CO
2
ambient condition. This process is defined as the
photosynthetic acclimation to high CO
2
concentration. Similarly, Frantz and Ling
(
2011
), recently observed a positive effect of CO
2
on leaf and flower mass after 5
weeks on the growth of
Petunia
×
hybrida
(second harvest), but there was no CO
2
effect on growth with the last harvest. These results show that long-term exposure
to elevated CO
2
doesn't always lead to enhanced biomass production. Moreover
photosynthetic acclimation can lead to adverse effects on the ornamental value
of plants (Croonenborghs et al.
2009
) such as higher carbohydrate concentration,
lower concentration of soluble proteins and RuBisCo, and inhibition of photosyn-
thetic capacity (Drake et al.
1997
).
Indeed higher amounts of carbohydrates can lead to a problem of source/sink
balances and sink strength. Arp (
1991
) analyzed the relationship between rooting
volume, or the size of the container, and acclimation of photosynthesis of plants
in elevated CO
2
concentrations and found that plants grown in small containers
(< 10 L), were sink limited because of root zone restrictions. These results were in
agreement with a survey of 163 studies by Drake et al. (
1997
), where the assimila-
tion remains the same for plants grown in both elevated and ambient CO
2
conclud-
ing that the restriction of rooting volume on acclimation is probably confounded
with effects of nutrient availability on photosynthesis.
Other factors, such as available nutrients, also could reduce sink strength (Drake
et al.
1997
). Qian et al. (
2012
) found that fruit load is important as well. By investi-
gating different fruit loads of tomato in a semi-closed greenhouse and a conventional
