Journal of Experimental Botany, Vol. 53, No. 378, pp. 2167-2176,
November 1, 2002
© 2002 Oxford University Press
Nitrogen dynamics in the intact grasses Poa trivialis and Panicum maximum receiving contrasting supplies of nitrogen
Received 14 January 2002; Accepted 25 June 2002
1 Escola Superior de Agricultura ‘Luiz de Queiroz’, Universidade de São Paulo, Av. Pádua Dias, 11, CEP 13400-000, Piracicaba-SP, Brazil
2 The Macaulay Institute, Craigiebuckler, Aberdeen AB15 8QH, UK
3 Present address and to whom correspondence should be sent: Embrapa Pecuária Sudeste, Rod. Washington Luiz-Km 234, Caixa Postal 339, CEP 13568-800, São Carlos-SP, Brazil. Fax: +55 19 3402 7583. E-mail: patricia{at}cppse.embrapa.br
The C3 grass Poa trivialis and the C4 grass Panicum maximum were grown in sand culture and received a complete nutrient solution with nitrogen supplied as 1.5 mol m–3 NH4NO3. 15N tracer techniques were used to quantify the relative use of root uptake and mobilization in supplying nitrogen to growing leaves in intact plants which either continued to receive nitrogen or which received the complete nutrient solution without nitrogen. The allocation of both 15N-labelled nitrogen uptake and unlabelled mobilized nitrogen indicated that, under their conditions of growth, the sink strength of growing leaves was relatively greater in P. maximum than P. trivialis. The supply of nitrogen by mobilization to side tillers of P. trivialis was completely stopped as the external nitrogen supply was reduced, whilst in P. maximum some allocation of mobilized nitrogen to side tillers, roots and growing leaves was maintained. In both plant species receiving an uninterrupted supply of nitrogen the allocation pattern of mobilized nitrogen differed from that of nitrogen derived from root uptake. Differences exist in the degree to which P. trivialis and P. maximum utilized uptake and mobilization to supply nitrogen to the growing leaves. In P. trivialis roots were always a net sink of mobilized nitrogen, irrespective of the external nitrogen supply. In P. maximum, roots were a net sink of mobilized nitrogen when external nitrogen was withdrawn, but exhibited both source and sink behaviour when nitrogen supply was continued.
Key words: Key words: C3, C4, leaf growth, N-mobilization, N-uptake, Panicum maximum, Poa trivialis.