Differential photosynthetic characteristics between seedlings and saplings of Abies sachalinensis and Picea glehnii, in the field

Abstract

AbstractAbies sachalinensis and Picea glehnii are co‐dominant tree species and major components of the forests of Hokkaido, Japan. Recent work suggests that a reversal in potential competitive superiority at different developmental stages could be important to explain their coexistence. Such shifts in competitive advantage can be mechanistically understood by studying the corresponding physiological differences between distinct life stages. Accordingly, our objective was to investigate in the field the photosynthesis of shade‐growing juveniles of these species from two different size‐classes, seedlings and saplings. Our results show that seedlings of both species had higher concentrations of photoprotective xanthophylls than saplings, especially in spring, and suggest that seedlings have a lower threshold of stress tolerance than saplings. Photosynthetic capacity per needle area and lateral shoot extension rate decreased from the seedling to the sapling stage in A. sachalinensis, while in P. glehnii, both increased from the seedling to the sapling stage. Abies sachalinensis had higher photosynthetic rates at the seedling stage but lower rates at the sapling stage than P. glehnii. Nevertheless, A. sachalinensis had a higher lateral shoot extension rate than P. glehnii at both stages. Our physiological results support previous ecological observations that A. sachalinensis is a superior competitor to P. glehnii in the understory, and show that its competitive advantage is higher at the seedling stage than at the sapling stage.