Roles of roots in successful growth of crop plants.For increasing dry matter production and high water use eficiency.

为提高水肥利用效率，研究了大气和土壤水分条件对作物根系发育和根系功能的影响，以及根系功能对作物生长和干物质生产的影响。主要研究结果如下：(1)比较了北海道札幌市和加利福尼亚州戴维斯市的马铃薯在灌溉和不灌溉条件下的根系发育。与灌溉条件下生长的植株相比，不灌溉条件下生长的植株根系发达。然而，在相同的灌溉处理下，在Davis种植的植株具有更大更密集的根系。(2)推导了估算水分利用效率的简单公式。这可能适用于玉米和棉花冠层，在一天的大部分时间里没有明显的放大。(3)在土壤水分不足的情况下，玉米植株在灌溉后，叶片衰老延缓，叶片光合作用速率保持在较高水平，与连续灌溉和不灌溉相比。灌水后根系分泌物急剧增加，分泌液中含有较高浓度的N、K等营养物质。(4)缺水条件下生长的玉米植株叶片由于衰老而导致的叶绿素含量和光合作用速率的下降被促进。植株从根向地上部运输的细胞分裂素和氮素总量减少。在土壤水分不足的情况下，茎内注入细胞分裂素抑制了植物叶片叶绿素含量和光合作用速率的下降。这一结果表明，在土壤水分不足的条件下，根系运输的细胞分裂素在维持叶片高叶绿素含量和高光合作用中起着重要作用。

The effects of atmospheric and soil moisture conditions on root system development and root functions and the effects of root functions on growth and dry matter production of crop plants were investigated for increasing water and fertilizer use efficiencies. The following results were obtained.(1) Potato plants were grown in Sapporo, Hokkaido and in Davis, California under irrigated and unirrigated conditions and root system development was compared. The plants grown under unirrigated conditions developed root system well compared with the plants grown under irrigated conditions. However, the plants grown in Davis had a larger and dense root system even under the same irrigation treatment.(2) Simple equations for estimating water use efficiency were derived. These might be applicable to maize and cotton canopies without explicit upscaling for most part of the day.(3) When maize plants were irrigated after grown under deficient soil moisture conditions, leaf senescence delayed and leaf photosynthetic rate was kept high significantly compared with the continuously irrigated plants and the unirrigated plants. Drastic increase of root exudation after the irrigation was observed and the exudation sap contained higher concentration of N, K and other nutrients.(4) The reduction in chlorophyll content and photosynthetic rate of a leaf due to senescence was promoted in maize plants growing under deficient soil moisture conditions. Total amount of cytokinin and nitrogen, transported to shoots from roots decreased in the plants. The infusion of cytokinin into a stem suppressed the reduction in leaf chlorophyll content and photosynthetic rate in the plants under deficient soil moisture conditions. This result indicate that cytokinin transported from roots would be important in keeping leaf chlorophyll content and photosynthetic rate high under deficient soil moisture conditions.