Dramatic altitudinal variations in leaf mass per area of two plant growth forms at extreme heights

Abstract

Knowledge of how leaf mass per area (LMA) and its components, leaf thickness (LT) and leaf density (LD), and related leaf traits may vary with altitude concerning different plant life forms at extremely high altitudes is scarce. We measured LMA, leaf nitrogen (Nmass), LT, LD, and the related anatomical characteristics of an evergreen shrub (Rhododendron aganniphum var. schizopeplum, RAS) and a wintergreen herb (Bergenia purpurascen, BP) along an altitudinal gradient above 4200 m a.s.l. to disclose how LMA for two different growth forms may vary with altitude and which leaf attribute determines the within-species variation of LMA. LMA significantly increased with rising altitude, at a pace of 40 g m−2/100 m for RAS and 12 g m−2/100 m for BP, respectively. LT was mainly responsible for the variability in LMA for RAS, and the variation of LT and LD contributed almost equally for BP. Nmass tended to decrease with rising altitude, and was negatively related to LMA and LT for both species. Foliar δ13C showed significantly rising trends with altitude, and was positively correlated with LMA and LT. The results indicated that plants at the extremely high altitudes are adapted to possessing especially higher LMA and steeper slopes of the relationships between LMA and altitude, as well as lower leaf nitrogen concentrations and higher δ13C to cope with the low-temperature environment. Compared with many other studies, LMA for both species are assumed to be more sensitive to the changing environment (especially warming). Also, Rhododendron shrub displayed steeper slope compared with dwarf herbs beneath the shrub layer indicating the former species should be more sensitive to warming climate. In all, exploring the plant strategies via leaf functional traits is of importance to understand the geography of evergreen species in alpine regions and its responses to future climate change.