Relationship between Understory Light and Growth of Forest-grown American Ginseng (Panax quinquefolius L.)

Our objective was to determine the relationship between daily and seasonal changes in understory light, and growth of 1- and 2-year-old american ginseng plants cultivated in a broadleaf forest. Using hemispherical photography and spectroradiometry, understory light [total, direct, and diffuse photon flux density (PFD), and sunfleck durations] and light quality [ultraviolet (UV) and red to far red (R:FR)] were evaluated during two consecutive growing seasons. While shoot and root dry weight (DW), and taproot area of 1-year-old american ginseng plants were related to sunfleck durations, accounting for up to 56% of the variation, the relationship reached a plateau at 2 h·d -1 sunfleck durations for growth. In September, growth of 1- and 2-year-old plants exposed to <2 h·d -1 sunfleck durations was positively related to diffuse PFD (and total PFD for 1-year-old plants), accounting for up to 69% of the variation. In mid-season (July 2000), shoot and root growth, and leaflet area of 2-year-old american ginseng were correlated with light PFD and light quality (UV and R:FR), accounting for up to 88% of the variation. Generally, the results suggest that exposing 1- and 2-year-old american ginseng plants to higher diffuse PFD and <2 h·d -1 sunfleck durations increases yield.