Nitrogen resorption and fractionation during leaf senescence in typical tree species in Japan
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ORIGINAL PAPER
Nitrogen resorption and fractionation during leaf senescence in typical tree species in Japan Ayako Enta1 · Mika Hayashi1 · Maximo Larry Lopez Caceres1 · Lei Fujiyoshi2 · Toshiro Yamanaka3 · Akira Oikawa1 · Felix Seidel1
Received: 2 November 2018 / Accepted: 4 March 2019 © The Author(s) 2019
Abstract In northeastern Japan, an area of high precipitation and mountains, beech (Fagus creanata Blume), larch (Larix kaempferi Lamb.), cedar (Cryptomeria japonica D. Don) and black locust (Robinia pseudoacacia L.) were evaluated for N resorption and N isotope fractionation in preand post-abscission leaves in comparison to green leaves. The highest leaf N concentration in summer corresponded to the N-fixing black locust, followed in decreasing order by the deciduous beech and larch and evergreen cedar. On the other hand, the lowest N resorption efficiency corresponded to black locust and the highest to beech, in increasing order by larch and cedar. All tree species returned significant amounts of N before leaf abscission; however, N isotope fractionation during leaf N resorption was only found for beech, with a depleted N isotope value from green to pre-abscission leaf. The most N, however, was resorbed from pre-abscission to post-abscission. This result may indicate that δ15N fractionation took place during N transformation processes, such as protein hydrolysis, when the concentration of free amino acids increased sharply. The difference in the type of amino acid produced by each species could have influenced the N
The online version is available at http://www.springerlink.com Corresponding editor: Yanbo Hu. * Maximo Larry Lopez Caceres [email protected]‑u.ac.jp 1
Faculty of Agriculture, Yamagata University, Wakabamachi 1‑23, Tsuruoka 997‑8555, Japan
2
Research Institute for Humanity and Nature, Motoyama 457‑4, Kamigamo, Kita‑ku, Kyoto 603‑8047, Japan
3
Department of Ocean and Environmental Sciences, Tokyo University of Marine Science and Technology, 4‑5‑7 Konan Minato‑ku, Tokyo 108‑8477, Japan
isotope ratio in beech but not in the other tree species. The results of this study showed that it is possible to infer the type and timing of processes relevant to N resorption by analyzing leaf δ15N variation during senescence. Keywords Amino acids · Cool temperate forest · Fresh litter · N resorption · δ15N
Introduction Nitrogen is one of the main elements necessary for forest ecosystem growth. However, its acquisition is limited by N mineralization and N loss through processes such as leaching and volatilization (Vergutz et al. 2012). Therefore, a key function for plants is the retention of nutrients via resorption from senescing leaves at the end of the growing season. Plants generally reabsorb half of their total leaf N, yet there is large interspecific variation in the extent of N resorption (Aerts 1996; Yuan and Chen 2009). The stored N is reallocated mainly to the stem and roots for new growing tissues the next spring (Millard 1994; van Heerwaarden et al. 2003; Singh 2014, 2015). N resor
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