Relationship Between Root Activity And Photosynthesis In Leaves Of Panax Ginseng

Panax ginseng is a typical herbaceous perennial shade plant, which is a traditional famous herb medicine of China, and are planted at large area in Jinlin province. Numerous studies had focused on the aerial parts photosynthetic physioecological research of Panax ginseng. However, to date, the relationship between root and photosynthesis in leaf of Panax ginseng have not been reported. Whether the growth stage changes and diurnal changes of photosynthesis have relationship to the changes of root activity? And how the root controls the photosynthesis of Panax ginseng? In this study the root bleeding sap weight (BSW) was as an index indicating root activity, the aerial parts of Panax ginseng plants were cut at the stem base and were inserted into the nutrient solutions contained different exogenous hormones which aim to simulate the influence of root to leaf photosynthesis. Then the root bleeding sap weight, leaf photosynthetic characteristics and water absorbing capacity (absorbing water weight) of the excised plants were menstruated at different growth stages. Expect to explore the reason of the photosynthesis changes of Panax ginseng, and provide certain theoretical basis of high yield culture in Panax ginseng.Research work was conducted in Ginseng garden of Jilin Agricultural University in2010and2011. The study was measured at flowering, green fruit, red fruit early and red fruit stage. The main experimental results are as follows:1. Changes of root bleeding sap weight, leaf photosynthesis and absorbing water weight of the excised plants at different growth stagesBleeding sap weight (BSW) of Panax ginseng at flowering stage was lower, at green fruit and red fruit early stage were highest and at red fruit stage was lowest. Then the leaf net photosynthetic rate (Pn) and absorbing water weight (AWW) of excised Panax ginseng at flowering stage were lower, at green fruit stage were highest, at red fruit early stage were higher and lowest at red fruit stage.2. Correlation of root bleeding sap weight to photosynthesis, absorbing water weight, chlorophyll content and specific leaf weightBleeding sap weight of Panax ginseng were positively correlated with leaf Pn, photosynthetic capacity (PC) and absorbing water weight at the growth stages, but there were obvious changes between bleeding sap weight with leaf Pn, PC and absorbing water weight at different growth stages. The ratio of leaf Pn and absorbing water weight to bleeding sap weight showed that at red fruit stage the water supply capacity of root was decreased sharply, but the leaf Pn and absorbing water weight were decreased slowly. Bleeding sap weight of Panax ginseng was positively correlated with chlorophyll content, but was negatively correlated with specific leaf weight. 3. Changes of stomatal conductance, transpiration rate and intercellular CO2concentration of Panax ginseng at different growth stagesThe stomatal conductance (Gs) and transpiration rate (7r) at flowering stage were lower, at green fruit stage were highest and decreased after green fruit stage, the Gs and Tr have the same change trend with leaf Pn. Intercellular CO2concentration (Ci) was highest at red fruit stage and lowest at green fruit stage.4. Diurnal changes of root bleeding sap weight and leaf photosynthetic characteristicsBleeding sap weight of Panax ginseng at a.m. was higher than p.m., leaf photosynthesis had a similar trend with bleeding sap weight, but the change ranges were different. The diurnal changes of leaf water use efficient (WUE) were not obvious, the changes of Gs and Tr were mainly to ensure the optimum condition of utilization of leaf to water.5. Effects of exogenous hormones on photosynthesis and absorbing water weight of Panax ginseng at different growth stagesExogenous abscisic acid (ABA) inhibited significantly leaf net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr) and absorbing water weight (AWW) of excised Panax ginseng at all growth stages, while both cytokinin (CTK) and auxin (IAA) enhanced their values.6. Growth stage changes and diurnal changes of effects exogenous hormones on photosynthesisExogenous ABA has more severe inhibition effects on photosynthesis at flowering and green fruit stage than red fruit early and red fruit stage. In addition, the inhibition effect of ABA on leaf Pn at early growth stage was more severe at p.m. than a.m. While CTK and IAA have more significant enhancement on photosynthesis at later growth stage than early growth stage, and at early growth stage the effects of CTK and IAA on photosynthesis were more significant at a.m. than p.m. ABA severely inhibited Ci at early growth stage, but not obvious at later growth stage. CTK and IAA have small effects on Ci at the whole growth stages.The results of this study showed that the root activity has close relationship with leaf photosynthesis of Panax ginseng. Different exogenous hormones have different effects on leaf photosynthesis. The inhibition effect of ABA on leaf Pn might be mainly due to the stomatal limitation at flowering and green fruit stages, while at red fruit early and red fruit stages might result from the combined effects of stomatal factor and other factors.