Correlation but no causation between leaf nitrogen and maximum assimilation: the role of drought and reproduction in gas exchange in an understory tropical plant Miconia ciliata (Melastomataceae)
Débora
Veiga
Aragão, Universidade Federal Rural da Amazônia, debora@ufra.edu.br
(Presenting)
Lucas
B
Fortini, University of Florida, lfortini@ufl.edu
Stephen
S.
Mulkey, University of Florida, smulkey@ufl.edu
Daniel
J
Zarin, University of Florida, zarin@ufl.edu
Maristela
Machado
Araújo, Universidade Federal Rural da Amazônia, maristela@ufra.edu.br
Cláudio José
Reis de Carvalho, Empresa Brasileira de Pesquisa Agropecuária, carvalho.bel@terra.com.br
We tested two alternative hypotheses that may explain a previously reported anomaly in the response of leaf Amax in Miconia ciliata (Rich.) DC to dry-season irrigation. The anomaly is characterized by an abrupt increase in leaf Amax values for non-irrigated plants at the onset of the rainy season that caused those values to significantly exceed corresponding measurements for plants that were irrigated during the previous dry season. Hypothesis 1 posits that a pulse in leaf nitrogen causes the increase of CO2 assimilation of non-irrigated plants at the onset of the wet season and is dampened for irrigated plants; this hypothesis was rejected because, although a wet-season nitrogen pulse did occur, it was identical for both irrigated and non-irrigated plants, and was preceded by the increase in assimilation by non-irrigated plants. Hypothesis 2 posits that a reproduction-related compensatory photosynthetic response occurs in non-irrigated plants following the onset of the wet season and is dampened in irrigated plants; consistent with hypothesis 2, high maximum assimilation rates for control plants in the wet season were significantly correlated with fruiting and flowering, whereas irrigation caused flowering and fruiting in the dry season, spreading M. ciliata reproductive activity in irrigated plants across the entire year. Water availability and reproductive phenology triggered by increased water availability are the primary factors that explain variance in leaf Amax for this species.
Submetido por Lucas Berio Fortini em 17-MAR-2004
Tema Científico do LBA: CD (Armazenamento e Trocas de Carbono)