Variation in fruit characteristics is frequently studied through the lens of frugivore preferences, but it may also be driven by the abiotic environment. Research on the reproductive ecophysiology of Rubus occidentalis (blackcap or black raspberry) is timely because of increasing interest in its antioxidant-rich fruits. Forty-nine R. occidentalis stands in southeastern Michigan were surveyed to 1) quantify variation in fruit characteristics in wild populations and 2) test for correlations between fruit characteristics and light and soil conditions. All fruit characteristics showed variation that strongly correlated with abiotic factors. Yield increased with increasing light, soil pH, and soil ammonium, and fruit fresh mass was positively related to light, soil fine particle fraction, and soil nitrate. Adjusting these factors may improve commercial yield and fruit quality for this species. Fruit water mass and water fraction were also higher in finer, more nitrate-rich soils. On the other hand, fruit dry mass increased with increasing light, implying that increased light availability may lead to better seed filling and better production of fruit solids. Fruit diameter was positively related to soil pH, soil fine particle fraction, and soil nitrate, and fruits had higher mass-to-diameter ratios in environments with higher light and in soils with lower organic matter content and loamier texture. Further study of the reproductive ecophysiology of R. occidentalis is clearly warranted.

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