Abstract
The leaf economics spectrum has given us a fundamental understanding of the species variations in leaf variables. Across plant species, tight correlations among leaf mass per area (LMA), mass-based nitrogen (Nm) and photosynthetic rate (Am) and leaf lifespan have been well known as trade-offs in leaf carbon economy. However, the regional or biome-level correlations may not be necessary to correspond with the global-scale analysis. Here, we show that almost all leaf variables in overwintering evergreen oaks in Japan were relatively well included within the evergreen-broadleaved trees in worldwide temperate forests, but Nm was more consistent with that in deciduous broadleaved trees. Contrary to the universal correlations, the correlation between Am and Nm among the evergreen oaks was negative and the correlation between Am and LMA disappeared. The unique performance was due to specific nitrogen allocation within leaves, i.e. the evergreen oaks with later leaf maturation had lower Nm but higher nitrogen allocation to photosynthetic enzymes within leaves, to enhance carbon gain against the delayed leaf maturation and the shortened photosynthetic period due to cold winters. Our data demonstrate that correlations between leaf variables in a local scale are occasionally different from averaged global-scale datasets, because of the constraints in each biome.
Highlights
Since the 1980s, it has been recognized that leaf lifespan (LLS) is one of the most important characteristics for determining plant strategies related to carbon and nitrogen (N) use, and the coordinated relationships among LLS, leaf morphology and physiology have been extensively examined [1,2,3,4]
The current-year leaves can make a substantial contribution to the total carbon gain in woody plants with a long LLS because the second-year leaves suffer from extensively reduced ribulose-1,5-bisphosphate carboxylase/oxgenage (Rubisco) activity [13] and self-shading owing to dense canopy [16]
We examined the leaf maturation process of the current-year leaves with respect to leaf size, leaf mass per area (LMA) and chlorophyll (Chl) accumulation for 1 year
Summary
Since the 1980s, it has been recognized that leaf lifespan (LLS) is one of the most important characteristics for determining plant strategies related to carbon and nitrogen (N) use, and the coordinated relationships among LLS, leaf morphology and physiology have been extensively examined [1,2,3,4]. In overwintering evergreen trees, the photosynthetically active period is shortened because of the cold winter [12,13], and these trees must enhance their desiccation tolerance via adaptations such as effective leaf osmotic adjustment during the winter season [14,15]. The late leaf flushing and the prolonged leaf maturation period should shorten the photosynthetically active period in the current-year leaves of overwintering evergreen woody plants growing in warm-temperate forests, near the 3 latitudinal or altitudinal limit, where minimum temperature drops below zero in the mid-winter. We examined how overwintering evergreen oaks in Japan compensate for the reduced carbon gain resulting from late leaf maturation and a shortened photosynthetic period in the current-year leaves. We discuss the implications of the specific leaf characteristics of overwintering oaks in Japan
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