Effects of nitrogen fertilizer, shade, and the removal of new growth on longevity of overwintering bog ericad leaves

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Abstract
Bog ericads, such as Labrador tea (Ledum groenlandicum), bog laurel (Kalmia polifolia), and leatherleaf (Chamaedaphne calyculata), retain individual leaves for two growing seasons in southern Ontario, presumably to facilitate nutrient movement between overlapping leaf cohorts. The objective of this study was to evaluate the effects of nutrient availability, shade, and the removal of new growth on the longevity of leaves during their second growing season. Longevity was extended significantly (p < 0.05) by removing new growth, but not by shading leaves (p > 0.05). The addition of nitrogen fertilizer increased only C. calyculata longevity. Interspecific variation in treatment effects appeared to be related to the positions occupied by the three species on environmental gradients. None of the experimentally treated leaves survived past the end of their second growing season, with the magnitude of treatment effects ranging from a reduction in longevity of 10 days to an increase of 25 days.