Nitrogen application enhanced the expression of developmental plasticity of root systems triggered by mild drought stress in rice

The promoted root growth under developmental plasticity triggered specifically by mild drought stress (MDS) is known to contribute to maintained water uptake and dry matter production (DMP). To examine whether the expression of developmental plasticity of root systems and its contribution to DMP would be affected by the levels of nitrogen (N) application. Two genotypes (CSSL50 derived from Nipponbare/Kasalath cross and Nipponbare) were grown under soil moisture gradients with a line source sprinkler system. Three N fertilizer treatments were used; 25 (low), 75 (standard) and 150 kg N ha(-1) (high) in 2009 and 60 (low), 120 (standard) and 180 kg N ha(-1) (high) in 2011. Across varying N level treatments, there were no significant differences in any of the traits examined between the two genotypes under well-watered and severe drought stress conditions. In contrast, under MDS conditions (15-25 % w/w of soil moisture content (SMC) in 2009 and 17-25 % w/w of SMC in 2011), CSSL50 showed greater DMP than Nipponbare. The difference, however, varied with N level treatments since CSSL50's greater root system development under MDS, was more pronounced at standard and high N levels than at low N level than it was for Nipponbare. N application enhanced the expression of plasticity in root system development at standard and high N levels as compared with low N level under MDS conditions, which contributed to the maintenance of DMP.