Lifetime leaf carbon balances of herbaceous perennial plants from low and high altitudes in the central Alps

1. A combination of demographic analysis of leaf growth, age-specific CO2 gas exchange and microclimate were employed to calculate lifetime sums of net photosynthesis and dark respiration, in order to obtain leaf carbon balances (Q(c)) of altitudinally disjunct Ranunculus and Geum species, as well as two altitudinal populations of Potentilla crantzii. If carbon costs for construction of leaf tissue are included, leaves fixed a lifetime carbon surplus ranging from 0.4 to 2.0 mmol CO2 cm(-2) independent of altitude, thereby exceeding initial investments by the plant three- to sixfold. 2. The lack of a consistent difference between the Q(c) of high and related low elevation taxa with similar leaf area ratios (LAR) challenges the view that carbon gain impairs growth and persistence of herbaceous perennials in harsh alpine climates to a greater extent than at low elevation. 3. Evidence from a sensitivity analysis of our carbon balance model as well as rank correlations indicate that the primary determinant of a leaf's carbon balance is its longevity. A comparison of leaf carbon balance data from the literature on wild plants of the temperate zone suggests that daily carbon gain on a leaf area basis is higher in herbaceous plants, compared to deciduous woody shrubs, which could explain the predominance of the herbaceous growth form at high altitudes.