Reduction in Leaf Water Potential and Hydraulic Conductance of Young Rice Plants (Oryza SativaL.) Grown in Wet Compacted Soils

摘要

Lower leaf water potential (ψ1) was observed in young rice plants grown in wet and highly compacted soil. Our objectives were to establish why the reductions of ψ1 occurred and to find the effect of plant hydraulic conductance on ψ1. One seedling of a lowland cultivar Nipponbare and an upland cultivar Senshou were grown in plastic pipes with a diameter of 5.4 cm and a height of 45 cm filled with a soil mixture. Soil bulk density (SBD) was set at four levels and wet soil conditions were maintained. In a growth chamber ψ1, transpiration rate per unit leaf area (TL), leaf area and root length were measured at 35 days after sowing. In both cultivars, plant hydraulic conductance (CP = –TL/ψ1) decreased as SBD increased and there was a positive correlation between CP and root length per unit leaf area. The greater decreases in root length than in leaf area, in the soil with a high bulk density, were suggested to reduce CP, thus resulting in lower ψ1. In both cultivars, root hydraulic conductance per unit root length (GR), estimated using a pressure-flux method, increased with increase in SBD. The increases in CR were accompanied by the increases in TL per unit root length at a high SBD. We suggest that the suppression of root length in rice by highly compacted soil causes lower GP which in turn reduces ψ1 even if the soil is wet. CR, water absorption rate per unit root length and the diameter of the primary roots, clearly increased under highly compacted soil conditions, but this might not be able to compensate for the greater reduction in root length than in leaf area, and so may not permit CP and ψ1 to be maintained.