THE EFFECTS OF PLANT DENSITY AND SNAIL GRAZING ON FEMALE AND MALE SPINACH PLANTS

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Summary

Male and female plants of the dioecious herb, Spinacia oleracea L. cv. Viking were grown in pots of five, 10 and 20 plants. Pots at each density were also exposed to grazing by the landsnail, Helix aspersa Muller (Helicidae; Gastropoda). Leaf longevity and rates of production for each of 13 leaf cohorts were determined for grazed and ungrazed female and male plants at each density. Dates of initiation of seed set and anthesis were recorded. At harvest, plant height, total dry weight and dry weights of leaves and stem, and of fruits and male reproductive organs were recorded. There were significant differences between females and males in time to anthesis, number of leaves per plant, leaf birth rate and reproductive effort. Females flowered and senesced later than males. Density had a significant effect on total number of leaves, leaf birth rate and leaf longevity. The only significant effect of snail grazing was a reduction in leaf longevity, particularly at the highest density. This corroborates recent suggestions that grazing has more effect on plants already exposed to relatively high levels of other pressures.

Ancillary