Abstract
Traditional Chinese medicine relies heavily on herbs, yet there is no information on how these herb plants would respond to climate change. In order to gain insight into such response, we studied the effect of elevated [CO2] on Isatis indigotica Fort, one of the most popular Chinese herb plants. The changes in leaf photosynthesis, chlorophyll fluorescence, leaf ultrastructure and biomass yield in response to elevated [CO2] (550±19 µmol mol–1) were determined at the Free-Air Carbon dioxide Enrichment (FACE) experimental facility in North China. Photosynthetic ability of I. indigotica was improved under elevated [CO2]. Elevated [CO2] increased net photosynthetic rate (P N), water use efficiency (WUE) and maximum rate of electron transport (J max) of upper most fully-expended leaves, but not stomatal conductance (gs), transpiration ratio (Tr) and maximum velocity of carboxylation (V c,max). Elevated [CO2] significantly increased leaf intrinsic efficiency of PSII (Fv’/Fm’) and quantum yield of PSII(ΦPS II), but decreased leaf non-photochemical quenching (NPQ), and did not affect leaf proportion of open PSII reaction centers (qP) and maximum quantum efficiency of PSII (Fv/Fm). The structural chloroplast membrane, grana layer and stroma thylakoid membranes were intact under elevated [CO2], though more starch grains were accumulated within the chloroplasts than that of under ambient [CO2]. While the yield of I. indigotica was higher due to the improved photosynthesis under elevated [CO2], the content of adenosine, one of the functional ingredients in indigowoad root was not affected.
Highlights
Global atmospheric CO2 concentration ([CO2]) is predicted to reach 550 mmol mol–1 by the middle of this century [1]
This study aims to address the following questions: (1) Will the leaf photosynthetic physiology, chlorophyll fluorescence and leaf mesophyll cell ultrastructure of I. indigotica be altered under elevated [CO2] and is there a correlation between them? (2) Will elevated [CO2] improve photosynthetic ability of I. indigotica and what is its implications for the yield and the functional ingredient adenosine of indigowoad root and leaf?
Photosynthetic acclimation has been well documented in C3 plants e.g. rice [24,25], soybean [23,26] and wheat [27], and the response varied with plant species, cultivars, developmental stages and environmental conditions [2,23]
Summary
Global atmospheric CO2 concentration ([CO2]) is predicted to reach 550 mmol mol–1 by the middle of this century [1]. Higher [CO2] increases the carboxylation rate of Rubisco but inhibits the oxygenation of Ribulose-1, 5-bisphosphate (RubP) [3]. These [CO2] effects vary with crops, cultivars and plant development stages. Chinese medicinal herbs are among the oldest alternative and complementary medicines. Their ever-increasing use indicates public interest in such medicines and their important roles. Chinese herbal medicines constitute multi-billion-dollar industries worldwide and 1500 herbals are sold as dietary supplements or ethnic traditional medicine. It is expected that there would be a greater boost in the use of Chinese herbal medicine [5]. The research on traditional Chinese medicine has been taken more and more seriously [7,8]
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