Abstract
The effect of two different CO2 concentrations (400 and 800 μmol mol−1) on the photosynthesis rate, primary and secondary metabolite syntheses and the antioxidant activities of the leaves, stems and rhizomes of two Zingiber officinale varieties (Halia Bentong and Halia Bara) were assessed in an effort to compare and validate the medicinal potential of the subterranean part of the young ginger. High photosynthesis rate (10.05 μmol CO2 m−2s−1 in Halia Bara) and plant biomass (83.4 g in Halia Bentong) were observed at 800 μmol mol−1 CO2. Stomatal conductance decreased and water use efficiency increased with elevated CO2 concentration. Total flavonoids (TF), total phenolics (TP), total soluble carbohydrates (TSC), starch and plant biomass increased significantly (P ≤ 0.05) in all parts of the ginger varieties under elevated CO2 (800 μmol mol−1). The order of the TF and TP increment in the parts of the plant was rhizomes > stems > leaves. More specifically, Halia Bara had a greater increase of TF (2.05 mg/g dry weight) and TP (14.31 mg/g dry weight) compared to Halia Bentong (TF: 1.42 mg/g dry weight; TP: 9.11 mg/g dry weight) in average over the whole plant. Furthermore, plants with the highest rate of photosynthesis had the highest TSC and phenolics content. Significant differences between treatments and species were observed for TF and TP production. Correlation coefficient showed that TSC and TP content are positively correlated in both varieties. The antioxidant activity, as determined by the ferric reducing/antioxidant potential (FRAP) activity, increased in young ginger grown under elevated CO2. The FRAP values for the leaves, rhizomes and stems extracts of both varieties grown under two different CO2 concentrations (400 and 800 μmol mol−1) were significantly lower than those of vitamin C (3107.28 μmol Fe (II)/g) and α-tocopherol (953 μmol Fe (II)/g), but higher than that of BHT (74.31 μmol Fe (II)/g). These results indicate that the plant biomass, primary and secondary metabolite synthesis, and following that, antioxidant activities of Malaysian young ginger varieties can be enhanced through controlled environment (CE) and CO2 enrichment.
Highlights
The increase of CO2 concentration in the atmosphere is well documented
The increase in phenolics concentration under elevated CO2 was parallel to an increase in photosynthesis rate and to an increase in the Total Soluble Carbohydrate (TSC) concentration, indicating higher availability of carbon to be invested in carbon based secondary compounds, which is in accordance with source-sinks theories for carbon based secondary compounds [59]
It would appear that atmospheric CO2 enrichment significantly enhances biomass production in ginger varieties, but that it slightly increases the concentrations of several therapeutic compounds
Summary
The increase of CO2 concentration in the atmosphere is well documented. A stimulation of plant growth, photosynthesis rate and biochemical composition under elevated CO2 are shown in most of the recent reviews [1,2,3]. Exposure of plants to elevated CO2 usually leads to increased rates of net photosynthesis due to enhanced activity of Rubisco enzyme and can alter plant growth and partitioning to secondary metabolites [2,3]. This can be proven from the result of the study by Wang: that elevated CO2 concentration in the atmosphere enhances vegetative growth, carbohydrate accumulation and fruit productivity in strawberry [4]. Such a reduction of stomatal conductance and diffusion may result in reduced vapor losses per unit of CO2 assimilated [8]
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