Leaf area development in response to meristem temperature and irrigation system in lowland rice

Growth and grain yield reductions have been widely observed when traditionally flooded rice fields were subjected to water-saving irrigation measures, where a continuous floodwater layer is avoided. These observations led to the perception of rice being a plant extremely sensitive to water stress even when grown in soils where water is sufficiently available. Since the rice plant's meristem is below the water surface during the vegetative stage in flooded fields, the difference in heat capacity between water and air will lead to changes in meristem temperature, when a ponded water layer is omitted. Therefore, the objective of this study was to investigate leaf area development in response to meristem temperature under flooded and non-flooded conditions in the field. In Ndiaye, located in the Senegal River valley, a lowland rice variety (IR64) was sown on 13 staggered dates between July 2008 and June 2010. In a flooded treatment (FL), a continuous water layer was maintained, whereas in a non-flooded treatment (NF), irrigation water was applied until soil saturation every 2 or 3 days. Temperature at the soil surface as well as leaf area and tiller number were recorded. In most cases, leaf area was reduced under non-flooded conditions. Leaf area expansion rate was correlated with meristem temperature during the night. With temperature at the soil surface being lower under non-flooded conditions, lower leaf area expansion rates under non-flooded conditions could be attributed to lower meristem temperature. The omission of a floodwater layer can expose the rice plant's meristems to larger temperature extremes and thus affect plant growth. In environments with large temperature amplitudes, this effect should be considered when water-saving measures are applied in lowland rice fields. (Résumé d'auteur