Background Allelopathic rice releases allelochemicals through its root systems, thereby exerting a negative effect on paddy weeds. This research aimed to evaluate the relationship between fine-root traits and the rice allelopathic potential at the seedling stage. Methods Two allelopathic rice cultivars, ‘PI312777’ and ‘Taichung Native1,’ and one non-allelopathic rice cultivar, ‘Lemont,’ were grown to the 3–6 leaf stage in a hydroponic system. Their fine roots were collected for morphological trait (root length, root surface area, root volume, and root tips number) in smaller diameter cutoffs and proliferative trait (root biomass) analysis. Their root-exudates were used for quantitative analysis of phenolic acids contents and an evaluation of allelopathic potential. Correlation analysis was also used to assess whether any linear relationships existed. Results Our results showed that allelopathic rice cultivars had significantly higher fine-root length having diameters <0.2 mm, more root tips number, and greater root biomass, coupled with higher allelopathic potential and phenolic acid contents of their root exudates, comparing with non-allelopathic rice cultivar. These fine-root traits were significantly-positively correlated to allelopathic inhibition and total phenolic contents in rice root-exudates. However, there were not significant correlations among the rice allelopathic potential and total phenolic acid contents of rice root-exudates with the root length, root surface area, and root volume of fine root in diameter >0.2 mm. Discussion Our results implied that fine-root traits appears to be important in understanding rice allelopathy at the seedling stage. The high allelopathic potential of rice cultivars might be attributed to their higher length of fine roots <0.2 mm in diameter and more number of root tips of fine root, which could accumulate and release more allelochemicals to solutions, thereby resulting in high inhibition on target plants. The mechanisms regulating this process need to be further studied.

Phenolic acid is a very important class of allelochemicals with allelopathic weed control activity. In this study, three benzoic acid derivatives (syringic, 4-hydroxybenzoic, and vanillic acids), three cinnamic acid derivatives (cinnamic, 4-hydroxycinnamic, and ferulic acids) were tested, and high-performance liquid chromatography was used to conduct a dynamic analysis on the changes in the concentration of phenolic acids in a bioassay based on the initial concentration and test time. The results showed that the concentration of individual phenolic acids and a solution of mixed phenolic acids decreased to a certain extent irrespective of environment, i.e., bioassay (4-7 days) or a ricegrowing environment, and a significant decrease in concentration was measured after 48 h. Based on the above results, the laboratory bioassay was conducted using a fresh solution of phenolic acids every 48 h. The results showed that the instability of phenolic acid could affect its weed control activity, and this effect was more significant for high concentrations of phenolic acids. On the other hand, changing the solution did not have a significant impact on the weed control activity of phenolic acids in the natural environment (pH 6.50), in which allelopathic rice release phenolic acids. These results reveal the instability of phenolic acids could significantly reduce the inhibition rate on the growth index for receptor plants in an indoor bioassay.

Aroma is one of the most important quality indicators of tea. However, this evaluation method is a subjective one. In this study, the volatiles of tea with 5 types were determined by headspace solid-phase micro-extraction (HS-SPME) combined with gas chromatography mass spectrometry (GC-MS). The aroma intensity and odor characteristics of teas were comparatively analyzed based on the OAV-splitting method. The results showed that OAV were green tea (492.02), red tea (471.88), oolong tea (302.74), white tea (68.10), and dark tea (55.98). The odor index I(o) indicated that green tea was strong-flavor tea with highlight green accompanied by fruity, woody and fatty odors; oolong tea was strong-flavor tea with fruity and fatty accompanied by woody, floral and green odors; red tea was strong-flavor tea with highlight fruity accompanied by woody, green and floral odors; white tea was a light-flavor tea with floral, woody and green odors; and dark tea was light-flavor tea with woody and floral notes accompanied by fatty and green odors. These results fitted perfectly with the people’s consensus on these teas, and proved that the OAV-splitting method is feasible to evaluate the aroma intensity and odor characteristics of tea aroma. We suggest that the digital evaluation of tea aroma can facilitate people’s communication.