Lifetime Leaf Carbon Balances of Herbaceous Perennial Plants from Low and High Altitudes in the Central Alps

Abstract

1. A combination of demographic analysis of leaf growth, age-specific CO 2 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 CO 2 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.