Polyphenol oxidase activity and its relationship to the soil main fertilizer factor in west Songnen alkali grassland Comparison in Contents of Polyphenol and Flavonoid in Leaves of Eucommia ulmoides Germplasm Changes in Defendant Enzyme Activity and Expression of PAL Gene of Stylosanthes after the Vaccination with Anthracnose Dynamic Changes of Polyphenols and Their Relationship with Antioxidant Capacity in the Muscat Hamburg Grapevine