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Seasonal changes in nitrate use by three woody species: the importance of the leaf-expansion period
Authors:Lina Koyama  Naoko Tokuchi  Keitaro Fukushima  Masakazu Terai  Yasuhiro Yamamoto
Institution:1. Biosphere Informatics, Department of Social Informatics, Graduate School of Informatics, Kyoto University, Kyoto, 606-8501, Japan
2. Laboratory of Forest Ecology, Graduate School of Agriculture, Kyoto University, Kyoto, 606-8502, Japan
3. Field Science Education and Research Center, Kyoto University, Kyoto, 606-8502, Japan
4. Laboratory of Silviculture, Division of Forest Science, Graduate School of Agriculture, Kyoto University, Kyoto, 606-8502, Japan
5. Division of International Resource Management, School of Agriculture, Kinki University, 3327-204 Nakamachi, Nara, 631-8505, Japan
Abstract:Seasonal changes in plant NO3 -N use were investigated by measuring leaf nitrate reductase activity (NRA), leaf N concentration, and leaf expansion in one evergreen woody species (Quercus glauca Thunb.) and two deciduous woody species Acer palmatum Thunb. and Zelkova serrata (Thunb.) Makino]. Leaf N concentration was highest at the beginning of leaf expansion and decreased during the expansion process to a steady state at the point of full leaf expansion in all species. The leaf NRA of all species was very low at the beginning of leaf expansion, followed by a rapid increase and subsequent decrease. The highest leaf NRA was observed in the middle of the leaf-expansion period, and the lowest leaf NRA occurred in summer for all species. Significant positive correlations were detected between leaf NRA and leaf expansion rates, while leaf N concentrations were negatively correlated with leaf area. In the evergreen Q. glauca, the N concentration in current buds increased before leaves opened; concurrently, the N concentration in 1-year-old leaves decreased by 25%. Our results show that the leaf-expansion period is the most important period for NO3 -N assimilation by broadleaf tree species, and that decreases in leaf N concentration through the leaf-expansion period are at least partly compensated for by newly assimilated NO3 -N in current leaves.
Keywords:Leaf expansion  Leaf nitrogen (N) concentration  Nitrate  Nitrate reductase activity (NRA)  Seasonal change
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