Abstract
A split plot 3 by 3 experiment was designed to investigate and distinguish the relationships among production of primary metabolites (soluble sugar and starch), secondary metabolites (total phenolics, TP; total flavonoids, TF) and leaf gas exchange of three varieties of the Malaysian medicinal herb Labisia pumila Blume, namely the varieties alata, pumila and lanceolata, under three levels of CO2 enrichment (400, 800 and 1,200 µmol mol−1) for 15 weeks. The treatment effects were solely contributed by CO2 enrichment levels; no varietal differences were observed. As CO2 levels increased from 400 to 1,200 µmol mol−1, the production of carbohydrates also increased steadily, especially for starch more than soluble sugar (sucrose). TF and TP content, simultaneously, reached their peaks under 1,200 µmol exposure, followed by 800 and 400 µmol mol−1. Net photosynthesis (A) and quantum efficiency of photosystem II (fv/fm) were also enhanced as CO2 increased from 400 to 1,200 µmol mol−1. Leaf gas exchange characteristics displayed a significant positive relationship with the production of secondary metabolites and carbohydrate contents. The increase in production of TP and TFs were manifested by high C/N ratio and low protein content in L. pumila seedlings, and accompanied by reduction in cholorophyll content that exhibited very significant negative relationships with total soluble sugar, starch and total non structural carbohydrate.
Highlights
The steady increase in atmospheric CO2 concentration due to climate change and/or agricultural practices is likely to affect biota by producing changes, in plant growth and allocation, and in plant tissue chemical composition [1]
L. pumila Blume partitioned more of the secondary metabolites to the leaves, followed by the roots and stems
Total flavonoids was enhanced by 80% and 95%, respectively, in 800 and 1,200 μmol mol−1 compared to 400 μmol mol−1 CO2
Summary
The steady increase in atmospheric CO2 concentration due to climate change and/or agricultural practices is likely to affect biota by producing changes, in plant growth and allocation, and in plant tissue chemical composition [1] Among such composition changes, most source-sink hypotheses (carbon nutrient balance hypothesis [2] and growth-differentiation balance hypothesis [3]). Assume that elevated CO2 concentration promotes a relative increase in carbon availability that is accumulated in total non structural carbohydrate (TNC) and carbon based secondary metabolites (CBSM) when the provided carbon amounts exceed growth requirements [4]. Several environmental factors affecting growth, photosynthesis and other parts of primary metabolism will affect secondary metabolism [2] These hypotheses predict a larger accumulation of carbon based secondary metabolites such as phenolics, terpenes or structural carbohydrates at elevated CO2. The increase in atmospheric CO2 concentration often increases total non structural carbohydrate (TNC) concentrations in plants that possibly stimulate the production of secondary metabolites [11]
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