Effects of Soil Moisture Depletion for One Month before Flowering on Dry Matter Production and Ecophysiological Characteristics of Wheat Plants in Wet Soil during Grain Filling

Effects of a Reduction in Soil Moisture from One Month beforeFlowering through Ripening on Dry Matter Production and Ecophysiological Characteristics of Wheat Plants

“…3). These results were identical to those obtained previously (Nakamura et al, 2003). Moreover, the CGR during the ripening stage was also higher in the plants in the D plot than those in the W plot (Fig.…”

“…Figure 4 shows the vertical distribution of roots in the soil in the two plots. The length of roots in the D plot was greater than that in the W plot in the soil at a depth of 40 to 80 cm but there were no differences in the shallower layers as Nakamura et al (2003) observed in the previous study. Any differences in root color could not be observed between the plants.…”

“…We found in a previous study (Nakamura et al, 2003) that wheat plants produced heavier dry matter, without a reduction in the leaf area index, under the conditions where rain was excluded and no irrigation was provided for about one month before fl owering, as compared with plants supplied with water in an amount that corresponds to an average year's precipitation or with plants grown under natural weather conditions. This result is quite different from the results obtained with summer crops, which suffer from water stress and markedly decreased leaf expansion and dry matter production when water is withheld for only a few weeks (Fujita et al, 2002, Hirasawa et al, 1994.…”

“…The development of root system can be promoted under moisture-defi cient conditions, even though it depends on the strength of the drought (Eghball and Maranville, 1993) and on both the species and the variety of plants Hida et al, 1995;Huang et al, 1997). A well-developed root system has also been reported in wheat plants grown under lower soil-moisture conditions (Proffi tt et al, 1985;Mian et al, 1993;Nakamura et al, 2003).…”

“…However, if soil moisture is insuffi cient to cause the damage due to a shortage of soil air, there must be other reasons for the reduction in dry matter production and yield under wet conditions, such as the effects on plant development, morphology and physiological characteristics, which differ from the mechanisms of wet injury considered to date. Nakamura et al (2003) considered that, in the ripening stage when the plants were grown with adequate moisture, the factor responsible for higher crop growth rate (CGR) in plants from which water had been withheld for about one month before fl owering was the slower leaf senescence inducing the maintenance of high leaf photosynthetic rate and large leaf area index (LAI). However, factors that cause the higher CGR in the plants during the month before fl owering, when the soil moisture and leaf xylem water potential were decreased to a greater extent under the conditions of decreased soil moisture, were not clarifi ed suffi ciently.…”