TITLE:
Effects of Root-Zone Temperature on Photosynthesis, Productivity and Nutritional Quality of Aeroponically Grown Salad Rocket (Eruca sativa) Vegetable
AUTHORS:
Jie He, Xin Er See, Lin Qin, Tsui Wei Choong
KEYWORDS:
Chlorophyll Fluorescence, Dietary Minerals, Root-Zone Temperature, Phenolic Compounds, Photosynthetic CO2 Assimilation Rate, Stomatal Conductance
JOURNAL NAME:
American Journal of Plant Sciences,
Vol.7 No.14,
October
17,
2016
ABSTRACT: Although tropical high ambient temperature and humidity
severely reduced the productivity of temperate plants, temperate vegetable crops
such as lettuce have been successfully grown in Singapore by only cooling its root-zone.
In this paper, a cool Meditteranean vegetable, Eruca sativa, was studied
to understand how different RZTs can impact its shoot productivity, photosynthesis
and nutritional quality. All plants were
cultivated using aeroponic systems in a tropical greenhouse under hot ambient conditions
where roots were subjected to four different root-zone temperatures (RZTs) of 20°C-RZT,
25°C-RZT, 30°C-RZT and fluctuating ambient temperatures ranged from
25°C to 38°C [25°C/38°C (ambient)]-RZT.
Parameters studied include shoot fresh weight (FW), photosynthetic gas exchange,
midday chlorophyll (Chl) fluorescence Fv/Fm ratio, Chl fluorescence
photochemical quenching (qP), non-photochemical quenching (qN) and electron transport
rate (ETR), total phenolic compounds and mineral content such as potassium (K),
calcium (Ca), magnesium (Mg) and iron (Fe). Among the 4 different RZT treatments, E. sativa plants grown
under ambient-RZT (25/38°C-RZT) had the lowest shoot and root FW while those
plants grown under 20°C-RZT had highest productivity
of shoot and root. However, there were no significant differences in shoot
and root FW in plants grown at 25°C- and 30°C-RZT. Compared to plants
grown under 25°C/38°C (ambient-RZT), light-saturated photosynthetic
CO2 assimilation rate (Asat)
and stomatal conductance (gssat)
were similarly higher in 20°C-, 25°C- and 30°C-RZT. All
plants had midday Chl fluorescence Fv/Fm ratio lower than
E. sativa plants protected their PS II from photoinactivation during midday in the
greenhouse. There were no significant differences observed in photochemical quenching
(qP), non-photochemical quenching (qN) and electron transport rate among plants
grown under 20°C-, 25°C- and 30°C-RZT. However, plants grown
under ambient-RZT had lower qP, qN and ETR compared to all other plants. E. sativa at 20°C-RZT with the best developed roots had the highest dietary mineral
(K, Mg, Ca and Fe) contents but lower total phenolics content. In contrast, ambient-RZT,
plants with poorly developed roots had the lowest mineral content but highest total
phenolic content. The results of this study suggest that cooling of roots is a feasible
method for the cultivation of E. sativa in the tropic, which enhances the
content of dietary minerals in shoots.