Cost–benefit relationships in fronds emerging at different times in a deciduous fern, Pteridium aquilinum

We studied the life-span and ecophysiological traits of "leaves" (fronds) that emerged at different times during the growing season in a deciduous herbaceous fern, Pteridium aquilinum (L.) Kuhn (in this paper we use "leaves" for fronds to be consistent with other studies on leaf phenology). Leaf life-span was shorter in later than in early cohorts. Leaf construction cost per unit mass was nearly constant among cohorts. Later cohorts had a lower leaf construction cost per unit leaf area with a lower leaf mass per area. Leaf life-span was positively correlated with construction cost per unit area. Late cohorts showed a slightly higher leaf nitrogen content per unit mass, but a lower nitrogen content per unit leaf area with a lower light-saturated photosynthesis per unit area. Light-saturated photosynthesis per unit area was positively correlated with leaf life-span. The ratio of leaf construction cost to light-saturated photosynthesis was lower in late cohorts, and the ratio was nearly proportional to leaf life-span, suggesting that late cohorts may pay back the construction cost despite their shorter life-span.Key words: leaf construction cost, leaf life-span, payback time, light-saturated photosynthesis, seasonal change.