Water Uptake under Water Stress at Panicle Initiation Stage in Upland Rice
as Affected by Previous Soil Water Regimes
K.Okada, M.Kondo, H. Ando and K.Kakuda
Soil Sci. Plant Nutrition 48-2, 159-164 (2002)
In situations of water stress, water uptake from the deep soil layer is a
key trait for drought avoidance in upland rice (Oryza sativa L.). In this
study, upland rice subjected to different soil water regimes during the vegetative
growth (low: -0.03 to -0.20 MPa and high: -0.03 to -0.09 MPa in soil matric
potential φS) was investigated to evaluate the daily plant water uptake of
root systems under short-term soil water stress at panicle initiation stage,
by characterizing the distribution of root length and changes of water extraction
per unit root length q (cm2 d-1) in different soil layers in a column experiment.
Irrigation was applied to set the φS at -0.03 to -0.04MPa at 0–20cm depth
and -0.02 to -0.03MPa in the layers below 20 cm depth in both soil water
regimes just before the imposition of the water stress treatment. In both
soil water regimes, daily plant water uptake decreased continuously during
the stress period, while the leaf water potential decreased substantially.
During the period 0–2 d after the last irrigation (DALI), water uptake rate
in the 0–20 cm layer was the largest among soil layers and coincided with
the largest root length. Subsequently, water uptake rate in the layers below
20 cm depth increased temporarily and then decreased rapidly as φS decreased,
while water uptake rate at 0–20 cm depth decreased monotonically. The q responded
to a decrease in φS differently in different layers in both soil water regimes.
In the 0–20 cm layer, q decreased continuously with a decrease in φS. On
the other hand, q in the layers below 20 cm depth increased with a decrease
in φS from the range of -0.02 to -0.03 to the range of -0.04 to -0.05 MPa.
However, as the φS decreased to below -0.05 MPa, the q in the layers below
20 cm depth decreased to a larger extent than did q in the 0–20 cm layer,
indicating limited root water extraction ability in those layers as water
stress developed, irrespective of soil water regimes. The root length in
the 20–40 cm layer increased in the low soil water regime by stimulating
branching of fine and medium roots (42–220 μm). Consequently, water uptake
rate in the 20–40 cm layer was larger in the low soil water regime, which
contributed to a larger daily plant water uptake at the beginning of the
stress period. In the later stress period, daily plant water uptake decreased
rapidly in both soil water regimes.
Key Words: column experiment, depth of soil layer, root water extraction,
upland rice (Oryza sativa L.), water stress
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