Md. Cramer et Mb. Richards, The effect of rhizosphere dissolved inorganic carbon on gas exchange characteristics and growth rates of tomato seedlings, J EXP BOT, 50(330), 1999, pp. 79-87
The possibility that an enhanced supply of dissolved inorganic carbon (DIC
= CO2 + HCO3-) to the root solution could increase the growth of Lycopersic
on esculentum (L,) Mill. cv, F144 was investigated under both saline and no
n-saline root medium conditions, Tomato seedlings were grown in hydroponic
culture with and without NaCl and the root solution was aerated with CO2 co
ncentrations in the range between 0 and 5000 mu mol mol(-1). The biomass of
both control and salinity-stressed plants grown at high temperatures (dail
y maximum of 37 degrees C) and an irradiance of 1500 mu mol m(-2) s(-1) was
increased by up to 200% by enriched rhizosphere DIG. The growth rates of p
lants grown with irradiances of less than 1000 mu mol m(-2) s(-1) were incr
eased by elevated rhizosphere DIC concentrations only when grown at high sh
oot temperatures (35 degrees C) or with salinity (28 degrees C), At high li
ght intensities, the photosynthetic rate, the CO2 and light-saturated photo
synthetic rate (J(max)) and the stomatal conductance of plants grown at hig
h light intensity were lower in plants supplied with enriched compared to a
mbient DIG. This was interpreted as 'down-regulation' of the photosynthetic
system in plants supplied with elevated DIG. Labelled organic carbon in th
e xylem sap derived from root (DIC)-C-14 incorporation was found to be suff
icient to deliver carbon to the shoot at rates equivalent to 1% and 10% of
the photosynthetic rate of the plants supplied with ambient- and enriched-D
IC, respectively. It was concluded that organic carbon derived from DIC inc
orporation and translocated in the xylem from the root to the shoot may pro
vide a source of carbon for the shoots, especially under conditions where l
ow stomatal conductance may be advantageous, such as salinity stress, high
shoot temperatures and high light intensities.