Relationships between leaf life span, leaf mass per area, and leaf nitrogen cause different altitudinal changes in leaf δ13C between deciduous and evergreen species

Abstract

We examined the variability in stable carbon isotope ratio (δ13C) in leaves of two deciduous broad-leaved species and two evergreen conifer species along an altitudinal gradient in central Japan. The δ13C of the two deciduous species decreased with altitude, except near the upper distribution limit. The two evergreen species, however, showed no clear altitudinal trends for δ13C. The δ13C of the two deciduous species was positively correlated with leaf mass per area (LMA), indicating that the altitudinal variation in δ13C was controlled by LMA. Leaf nitrogen per mass (as a proxy of assimilation capacity, Nmass) was negatively correlated with LMA for the two deciduous species, while it was not correlated with LMA for the two evergreen species. Leaf life span of the two deciduous species decreased with altitude, whereas that of the two evergreen species increased. Thus, the two deciduous species had shorter-lived thinner leaves with higher Nmass at higher altitudes, and the two evergreen species had longer-lived leaves. These changes contribute to the positive carbon balance at higher altitudes. Therefore, the different changes in δ13C with altitude between the deciduous and evergreen species are ascribed to the different altitudinal changes in the leaf traits for carbon balance.