Influence of soil water deficits on maize growth and leaf area adjustments

Physiological aspects of leaf growth, leaf movements and morphological mechanisms have been studied extensively. However, there has been little effort to elucidate the adaptative importance of either of these types of leaf area adjustments during water deficit. The objective of this study was to: (i) identify morphological and physiological differences between two maize hybrids; (ii) Define the relation between LAI and radiation interception; (iii) Characterize the sensitivity and quantify the contribution of leaf rolling, leaf senescence and leaf expansion to the reduction of plant exposed leaf area and; (iv) Modify the CERES-Maize model to predict the daily fraction of radiation intercepted by maize plants. Pioneer varieties 3576 and 3615 were subjected to three irrigation managements: Well-irrigated, pre-anthesis water deficit and post-anthesis water deficit. Spinks loamy sand and Kalamazoo loam were the soils used. Post-anthesis soil water deficit was not imposed on the Kalamazoo loam soil. Results indicate that as the water deficit developed the maize tended to orientate its leaf blades in a more vertical position. The PAR interception declined for both maize varieties during the vegetative soil water deficit period due mainly to an increase in leaf rolling and a change in leaf orientation and, to a decrease in leaf expansion. Leaf rolling and leaf expansion were influenced by periods of low VPD. Plant leaf rolling limited the activity of the leaf elongation mechanism. During post-anthesis soil water deficit plant leaf rolling was reduced due to length and width of the leaf blades (long leaf blades bend downwards). Thus, leaf rolling mainly occurred near the edges of the leaves, limiting further increases in leaf rolling and leaf orientation and, consequently, the reduction of exposed leaf area. The effectiveness of the leaf rolling mechanism, during post-anthesis water deficit, occurred mainly during the beginning of the water deficit period and leaf senescence was activated later when no further reduction in exposed plant leaf area was possible by increasing leaf rolling. Modifications in the CERES-Maize model enabled the model to predict intercepted PAR and the fraction of plant leaf area exposed to the incident solar radiation.