Migita Chiharu, Chiba Yukihiro, Tange Takeshi
Graduate School of Agricultural and Life Sciences, the University of Tokyo, Tokyo 113-8657, Japan.
Tree Physiol. 2007 Jan;27(1):63-70. doi: 10.1093/treephys/27.1.63.
To elucidate the relationships between spatiotemporal changes in leaf nitrogen (N) content and canopy dynamics, changes in leaf N and distribution in the canopy of a 26-year-old deciduous oak (Quercus serrata Thunb. ex. Murray) stand were monitored throughout the developmental sequence from leaf expansion to senescence, by estimating the leaf mass and N concentrations of all the canopy layers. Seasonal changes were observed in leaf N concentration per unit leaf dry mass (N (m)), which peaked after bud burst, declined for two weeks shortly thereafter, and then remained constant for the rest of the growing season for each canopy layer. Leaf N concentration per unit leaf area (N (a)) was higher in the upper layer than in the lower layer throughout the growing season, and was closely correlated with relative irradiance (RI) in the summer when the air temperature was moderately high. The N concentrations of all leaf layers started to decrease in November, and reached their lowest values in late November, whereas LMA scarcely changed throughout the season. The lowest N concentrations did not differ significantly among the canopy layers. Seasonal changes in the relationship between N (a) and RI were detected, indicating that N (a) is optimized temporally as well as spatially. Nitrogen resorption efficiency was highest in the upper canopy layers where larger amounts of N were invested. Based on the estimates of leaf mass and leaf N concentrations of the canopy layers, total leaf N concentration of the whole canopy was estimated to be 84.1 kg ha(-1) in the summer, and 37.3 kg ha(-1) in late November. Therefore, 46.8 kg ha(-1) of leaf N in the canopy (about 56% of the total N) was resorbed just before leaf abscission.
为阐明叶片氮（N）含量的时空变化与冠层动态之间的关系，通过估算所有冠层的叶片质量和氮浓度，对一个26年生落叶栎（Quercus serrata Thunb. ex. Murray）林分从叶片展开到衰老的整个发育过程中叶片氮的变化及其在冠层中的分布进行了监测。各冠层单位叶干质量的叶片氮浓度（N（m））呈现季节性变化，在芽萌发后达到峰值，此后短期内下降两周，然后在生长季剩余时间保持稳定。整个生长季中，单位叶面积的叶片氮浓度（N（a））在上层高于下层，并且在夏季气温适中时与相对光照强度（RI）密切相关。所有叶层的氮浓度在11月开始下降，并在11月下旬达到最低值，而叶质量面积比（LMA）在整个季节几乎没有变化。最低氮浓度在各冠层之间没有显著差异。检测到N（a）与RI关系的季节性变化，表明N（a）在时间和空间上都得到了优化。氮素重吸收效率在投入大量氮的上冠层中最高。根据冠层各层叶片质量和叶片氮浓度的估算，整个冠层的总叶片氮浓度在夏季估计为84.1 kg ha⁻¹，在11月下旬为37.3 kg ha⁻¹。因此，冠层中46.8 kg ha⁻¹的叶片氮（约占总氮的56%）在叶片脱落前被重吸收。
