Root growth and distribution in rice cultivars as affected by nitrogen and water supply

Abstract

Aims Quantitative study of root growth pattern in rice(Oryza sativa) is of great significance for guiding man-agement regulation and genetic improvement.Our objective was to elucidate the characteristics of root growth and distribution in rice under different conditions of cultivation.Methods We conducted pot experiments involving different nitrogen rates,water regimes and rice cultivars with the root shelf method.Root indices were measured at the jointing and heading stages,including total dry weight(TRW),adventitious root number(ARN),and morphological indices(length,surface area and volume) of three types of roots(adventitious,fine and coarse lateral roots).Important findings The observed root indices increased from the jointing stage to the heading stage in all treat-ments.There were significant differences in root indices among the three nitrogen rates,and each index increased with increasing nitrogen rates at both stages.In the water regime experiment,there was no significant difference in ARN between irrigation(W2) and constant water(W1),but the other indices of W2 were highest at both stages.There were no significant differences in TRW and morphological indices of coarse lateral roots between W1 and dry cultivation(W3) at the jointing stage.The other indices at the jointing stage and all indices at the heading stage were lowest with W3.All indices were significantly highest in the 'Yangdao 6'(V3) cultivar,but similar in 'Nipponbare'(V1) and 'Wuxiangjing 14'(V2) cultivars.In addition,the roots extended more deeply into soil from the jointing to the heading stage,but were mainly distributed in the top 5 cm.Lower nitrogen and water supply would promote spreading of roots in the subsoil(5 cm) and enhance the proportions of fine and coarse lateral roots.As compared with V3,the roots of V1 and V2 extended more deeply into soil.We concluded that proper nitrogen fertilization and water control could optimize the growth and distribution characteristics of different types of rice roots and this could be influenced by the specific cultivar.