Seasonal patterns of leaf physiological traits, nutrient and adaptive strategies of co-occurring Alnus nepalensis and Quercus leucotrichophora tree species in the central Himalaya

We compared seasonal leaf gas exchange patterns, photosynthetic pigments, and photosynthetic nutrient use efficiencies in two co-occurring tree species, Nepalese alder (Alnus nepalensis D. Don) and white oak (Quercus leucotrichophora A. Camus), in the central Himalaya. In both species, area-based and mass-based photosynthetic CO2 assimilation rates, stomatal conductance, leaf nutrient concentration, photosynthetic nutrient use efficiency, and leaf chlorophyll pigments peaked in summer, while water use efficiency peaked in autumn. In spring, summer, and autumn, values for most parameters (specific leaf area, relative water contents, area-based and mass-based photosynthetic CO2 assimilation rates, leaf nutrient concentration, photosynthetic nutrient use efficiencies, and leaf chlorophyll pigments) were higher in A. nepalensis than in Q. leucotrichophora. In winter, however, values for area-based CO2 assimilation rates, water use efficiency, leaf calcium, leaf magnesium concentration, and photosynthetic pigments were higher in Q. leucotrichophora than in A. nepalensis. We conclude that A. nepalensis exhibits a more resource-acquisitive strategy, characterized by higher levels of leaf nutrients and nutrient use efficiencies, that supports higher photosynthetic capacity. In contrast, Q. leucotrichophora exhibits a resource-conservative strategy with higher construction cost.