Abstract
Rainfed lowland (RFL) rice fields have hardpans and experience soil moisture fluctuations (SMF) stress, which influence root system development. Here, we clarify the expression and timing of the plasticity in nodal root elongation through the hardpan under SMF and its contribution to shoot growth using a shallow-rooting IR64 and its deep-rooting introgression line, YTH304. Under SMF, soil moisture content had negative relationship with soil penetration resistance, regardless of hardpan bulk densities. YTH304 had greater root system below the hardpan than IR64 in hardpan with 1.50 but not in 1.70 g cm−3 bulk density (BD). YTH304 had greater plasticity in nodal root elongation through the hardpan than IR64 under SMF, which was clearly expressed during rewatering. YTH304 also had greater soil water uptake below the hardpan during drought and greater shoot growth than IR64. The results imply that deep root system development during SMF was due to the plasticity in nodal root elongation through the hardpan expressed during rewatering rather than during drought periods. This is against the long standing belief that active root elongation through the hardpan happens during drought. This also implies a need to revisit current root screening methods to identify rice lines with good hardpan penetration ability.
Highlights
Rice in rainfed lowland (RFL) ecosystems generally yields lower than in irrigated lowlands
To examine the plasticity in nodal root elongation through the hardpan under different soil moisture conditions during soil moisture fluctuations (SMF), we developed a rootbox-hardpan experimental system that can be embedded with 5-cm thick hardpan with variable level of bulk density (BD) at 16 cm below the soil surface (Supplementary Fig. S1)
Since the artificial hardpan was made from a mixture of soil and kaolinite, its penetration resistance (PR) can interact with changes in soil moisture during SMF
Summary
Rice in rainfed lowland (RFL) ecosystems generally yields lower than in irrigated lowlands. The ability for deep root system development allowed the access of a greater volume of water from the deeper soil layer during periods of drought[1,17,18,19,20,21,22] Both of which have been suggested to improve adaptation to RFL conditions. Soil PR generally interacts with moisture availability[24,38,39] and the magnitude of soil strength[38,39,40] Under this condition, root growth is decreased by both the increase in PR (water is not limiting) and intensity of drought stress (PR is not limiting)[41]. The hardpan PR in RFL rice fields may influence the expression of root plasticity in response to soil moisture fluctuations
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