© 1995 Heron Publishing—Victoria, Canada
Role of nitrogen remobilization from old leaves for new leaf growth of Eucalyptus globulus seedlings
R. Wendler (1), P. O. Carvalho (2), J. S. Pereira (2) and P. Millard (1, 3)
1. Macaulay Land Use Research Institute, Craigiebuckler, Aberdeen AB9 2QJ, U.K. / 2. Instituto Superior de Agronomia, Universidade Técnica de Lisboa, Tapada da Ajuda, P-1399 Lisboa Cedex, Portugal / 3. Author to whom correspondence should be addressed / Received October 17, 1994
Summary
Six-month-old Eucalyptus globulus Labill. seedlings were grown in sand culture irrigated with a nutrient solution containing 6.0 mol N m–3 for 3 months (November–January). Before rapid growth began in February, seedlings were repotted and irrigated with either
6.0 mol N m–3 (High-N treatment) or 1.0 mol N m–3 (Low-N treatment). Seedlings were analyzed during the subsequent flush of growth to determine the role of old leaves, and
in particular the leaf protein Rubsico, as a source of N for new leaf growth.
During spring growth, the N content of old leaves of High-N seedlings decreased with decreasing leaf dry weight, although
there was no change in leaf number. In High-N seedlings, the net loss of N from old leaves provided less than 10% of the N
used for new leaf growth, and the new leaves quickly became the dominant sink for N. In contrast, in Low-N seedlings, the
net loss of N from old leaves provided 44% of the N used for new leaf growth. During the period of spring growth, the amount
of soluble proteins recovered from old leaves of Low-N seedlings dropped, but there was no change in the content of either
Rubisco or chlorophyll. The photosynthetic capacity of old leaves remained constant throughout the study period, and there
was no evidence that N was remobilized from Rubisco.
Keywords:
canopy nitrogen, dynamics, internal cycling, photosynthetic capacity, Rubisco, storage.
