Effects of elevated CO on foliar soluble nutrients and functional components of tea, and population dynamics of tea aphid, Toxoptera aurantii.

The rising atmospheric CO concentration has shown to affect plant physiology and chemistry by altering plant primary and secondary metabolisms. Nevertheless, the impacts of elevated CO on plant nutrients and functional components of tea remain largely unknown, which will likely affect tea quality and taste under climate change scenario. Being sources of nutrients and secondary chemicals/metabolites for herbivorous insects, the variation in foliar soluble nutrients and functional components of tea plants resulting from CO enrichment will further affect the herbivorous insects' occurrence and feeding ecology. In this study, the tea aphid, Toxoptera aurantii was selected as the phloem-feeding herbivore to study the effects of elevated CO on foliar soluble nutrients and functional components of tea seedlings, and the population dynamics of T. aurantii. The results indicated that elevated CO enhanced the photosynthetic ability and improved the plant growth of tea seedlings compared with ambient CO, with significant increases in net photosynthetic rate (+20%), intercellular CO concentration (+15.74%), leaf biomass (+15.04%) and root-to-shoot ratio (+8.08%), and significant decreases in stomatal conductance (-5.52%) and transpiration rate (-9.40%) of tea seedlings. Moreover, elevated CO significantly increased the foliar content of soluble sugars (+4.74%), theanine (+3.66%) and polyphenols (+12.01%) and reduced the foliar content of free amino acids (-9.09%) and caffeine (-3.38%) of tea seedlings compared with ambient CO. Furthermore, the relative transcript levels of the genes of theanine synthetase (+18.64%), phenylalanine ammonia lyase (+49.50%), s'-adenosine methionine synthetase (+143.03%) and chalcone synthase (+61.86%) were up-regulated, and that of caffeine synthase (-56.91%) was down-regulated for the tea seedlings grown under elevated CO relative to ambient CO. In addition, the foliar contents of jasmonic acid (+98.6%) and salicylic acid (+155.6%) also increased for the tea seedlings grown under elevated CO in contrast to ambient CO. Also, significant increases in the population abundance of T. aurantii (+4.24%-41.17%) were observed when they fed on tea seedlings grown under elevated CO compared to ambient CO. It is presumed that the tea quality and taste will be improved owing to the enhanced foliar soluble nutrients and functional components of tea seedlings under the climate change scenario, especially on account of the rising atmospheric CO concentration, while the climate change may exacerbate the occurrence of tea aphid, T. aurantii, despite the enhanced secondary defensive chemicals manifested by the CO enrichment.