Leaf-level nitrogen-use efficiency of canopy and understorey species in a beech forest (original) (raw)

In a forest stand, canopy and understorey species grow at completely different irradiances and consequently with different carbon and nitrogen availability ratios. We studied how the difference in growth irradiance influenced plant N use in a mature beech forest. 2. We defined leaf-level nitrogen-use efficiency (NUE L ) as the amount of the leaf dry mass produced per unit N taken up by leaves. NUE L was similar between the canopy species ( Fagus crenata ) and the understorey species ( Lindera umbellata and Magnolia salicifolia ). 3. NUE L was analysed further as the product of two components: leaf-level N productivity (NP L ) and mean residence time of leaf N (MRT L ). The canopy species had significantly larger NP L and significantly shorter MRT L than the understorey species. 4. As the photosynthetic capacity was similar among the species, different NP L between the species was attributable largely to the difference in light conditions to which their leaves were exposed. 5. The difference in MRT L was not attributable to potential efficiency of N resorption ( R EFF ) determined at leaf senescence, but to actual R EFF , which depended on the amount of green leaf lost before full senescence. The canopy species had significantly smaller actual R EFF because of strong wind actions in the canopy. 6. Although the canopy species realized higher NP L by virtue of high irradiance, it had shorter MRT L due to wind damage to pre-senescent leaves. On the other hand, the canopy species had shorter NP L under shady conditions, but had longer MRT L with little wind damage. Interplay of local environmental factors such as light and wind strongly influenced N use by plants in the beech forest.