水稻根系在根袋处理条件下对氮养分的反应

通过大田试验对 1 0个水稻品种根系与产量的关系研究表明 ,抽穗期和成熟期根冠比与产量呈极显著的负相关关系 ,相关系数分别为 - 0 .861 6和 - 0 .8889。随之在大田试验基础上选择根冠比大的品种粳籼89,设计水分和养分能自由通过 ,而根系不能穿过的根袋 ,根袋从小到大不同 ,以便产生不同大小的水稻植株根冠比。通过水培实验研究在根袋处理后对不同养分条件的反应。水培液设 3种氮素养分水平 ,即2 0 mg/kg,40 mg/kg,60 mg/kg。结果表明 ,在不同氮素养分条件下 ,经过根袋处理后在抽穗期根系干重都有下降趋势 ,根冠比显著降低 ,而根系活性吸收面积在抽穗期有不同程度的增加 ,茎鞘贮存性碳水化合物含量明显增加 ,叶绿素含量则无明显影响。在抽穗期较大的根袋处理根系总吸收面积、活跃吸收面积及所占比例与对照相比增加效果较为明显 ,而较小的根袋处理根系吸收的能力降低 ,根系吸收能力大小顺序为 :大袋 >中袋 >对照 >小袋。随养分浓度的增加 ,不同根袋处理在抽穗期的根系总吸收面积和活跃吸收面积有下降的趋势。较大的根袋处理在 2 0 mg/kg和 60 mg/kg氮素养分条件下能适当减少根系直径 ,增强根系的活性吸收比例 ,从而提高根系的活力 ;但在成熟期根袋处理对根系的活性吸收无明显影响

The response of the rice root system to nitrogen conditions under-root confinement

Under the conditions of ample water and nutrients, production of an excess root system may reduce the growth of shoots because of the competition of carbohydrates between roots and shoots. Roots are the major sink for assimilates, requiring twice as much assimilate to produce per unit dry matter as the shoots. Passioura( 1983) doubted that the root system of many crop plants may be excessive; and suggested that smaller root system may be beneficial for assimilate to be transferred to shoots. Based on the assumption that varieties with large root/shoot ratios may exist root redundancy, ten common rice varieties were used to study the relationships between root biomass, shoot biomass and yield in field experiments. The results showed that root/shoot ratios at heading and ripening stages were negatively correlated with yield(correlation coefficients were -0 8616 and -0 8889, respectively) but root weight was not. So root system redundancy existed for those rice varieties with large root/shoot ratio in terms of maximizing yield . A hydroponic experiment was conducted to further elucidate the relationship between root and shoot development and yield. Root system was placed in cylindrical nylon bags to result in root confinement. Different sizes of nylon bags allowed movement of water and nutrients but prevented penetration of root. The diameters of the root bags were 3cm(R3), 4cm(R4), 5cm(R5) respectively and the length was 25cm. Rice grown in the absence of a nylon bag was used as a control(R0). Different root/shoot ratios could be realized through root confinement methods. The variety Jingxian 89 with large root/shoot ratio and nitrogen levels of 20mg/kg, 40mg/kg and 60mg/kg for the hydroponic solutions were used in this experiment. Rice grown with a confined root system at different N levels had significantly lower root/shoot ratios, higher total surface area(TSA),active absorption area(ASA) and ASA/TSA ratio at heading stage. The root/shoot ratio at the low N level was reduced by 21.94%, 4.64% and 15.54% and at the medium N level, were reduced by 21.51%, 15.13%, 22.45%, when roots were confined to bags with the diameter of R3, R4 and R5, respectively. The reserved carbohydrate content, especially the soluble sugar in the stem and sheath of the rice plant also increased significantly. The chlorophyll content in the functional leaves were not affected by root confinement. Moderate root confinement increased TSA, ASA and ASA/TSA ratio than other root confinement at different nutrient levels, but root system activity decreased with severe root confinement. With the increase of N concentration, TSA, ASA of the root system decreased in all treatments. These results suggest that root system competition decreased with the increase in N nutrient level. Moderate root confinement could reduce root diameter, increase active root absorption and root activity at heading. However, root confinement had no effects on root surface area and active absorption area at ripening. These results suggest that reduction of root/shoot ratio may be beneficial to increase root system activity, and promote more carbonhydrate transferred to the shoot.