A large number of studies and reports have been made on the formation of rice yield and the growth of aboveground organs. Due to research methods and workload issues, relatively little research has been done on the rice root system. Moreover, the limited research on rice roots in China mostly uses hydroponics. The root growth under hydroponic environment is obviously different from that under soil culture conditions. This may be the main reason why foreign research on rice roots adopts the method of soil culture.

Due to the close relationship between roots and shoots and the importance of yield, people attach great importance to root traits in the breeding of super high-yielding rice varieties. Although it has been noted that deep roots are closely related to yield formation, the main time for deep root formation is important. And the impact factor is not clear enough. This paper studies the root growth characteristics and the response to soil bulk density in different growth stages of rice, and explores the morphological physiology and regulatory pathways of root growth.

2 Materials and Methods

2.1 The test materials The tested varieties were hybrid rice indica 63 in 1998, and hybrid rice combinations 63 and 65002 in 1999. The rice root development was measured using a root analyzer during growth of the two rice varieties.

2.2 Research Methods

2.2.1 Planting methods

Experiment 1: The experiment was conducted in the Chinese Rice Research Institute's net room in 1998 and 1999. A PVC tube with a diameter of 20 cm and a height of 50 cm was used. Each tube was planted with 1 cluster, and 1 or 2 plants were planted in each bundle. Each treatment was repeated 3 times. The PVC tube is filled with soil from the bottom up to 45cm. The soil in the tube simulates the soil bulk density of the field and is divided into 2 layers of eroded loam soil and fine sand mixed soil. The fine sand is about 30%. The lower 50~25cm soil bulk density is 113g#cm-3. After the upper layer of 25~5cm soil is filled with water, the soil is allowed to sink naturally. The rice is sown on May 25th and transplanted on June 24th. The seedlings with the same plant height and tiller growth are transplanted in each tube. The N amount is 180kg#. Hm-2, in which base fertilizer, tiller fertilizer and panicle fertilizer are applied as 6B215B115, applied calcium phosphate 450kg#hm-2 as basal fertilizer, and KCl 150kg#hm-2, 50% of which is basal fertilizer, and the other 50% is sub-fertilizer. .

Test 2: The test site and the test variety are the same as test 1. A PVC tube with a diameter of 30 cm and a height of 50 cm is used, and three different soil volume weights are set for processing. The 50-25 cm soil layer volume density is 112 g #cm-3 (S1), respectively. 114g#cm-3(S2) and 116g#cm-3(S3). After the upper 25~5cm soil is filled with water, allow the soil to sink naturally. Plant 1 plant per tube and repeat it twice. The fertilizer and water management is the same as the test 1. The root dry weight was measured at the flowering stage.

2.2.2 Sampling Method and Root Weight Measurement

Test 1 Sample root growth at the time of tillering, panicle differentiation, flowering, and ripening. When sampling, remove the soil in the PVC cylinder and use a wire saw to saw the soil column from top to bottom at a distance of 10 cm and at a distance of 5 cm. The soil column obtained from PVC was placed on a 015cm mesh sieve, rinsed in water, and the root system was dried in a 70e oven to a constant weight to give the dry weight of the root system.

2.2.3 Vertical Distribution of Roots

The vertical distribution of the roots of soil columns with different depths of soil takes the middle point of the soil column as the vertical column, and uses the 1/2 of the soil column root weight as the abscissa to obtain the vertical distribution of the root system.

3 Results and Analysis

3.1 Root Weight Growth of Rice

The growth of roots in different periods of rice has undergone growth and senescence.

The weight of roots was the largest in flowering stage. The weight of roots from the tillering stage to the flowering stage was the growth stage, and the flowering stage was the descending stage. The growth trend of the root system in 1998 was the same as the trend in 1999. The data in 1999 are used as an example to illustrate the total rooting of the flowering stage. Except for Shanyou 63, the other treatments were significantly higher than other periods, and the rooting volume at the tillering stage was significantly lower than that at other stages (Table 1). 65502 The weight of the root system from the tillering stage to the panicle differentiation stage and panicle differentiation stage to the flowering stage With an increase of 519 and 411 g, the root volume declined from the flowering stage to the mature stage by an average of 218 g. The root weight of Shanyou 63 increased by 517 and 214 g from the tillering stage to the panicle differentiation stage and panicle differentiation stage to the flowering stage. The average root volume declined from flowering to maturity. 114g (Table 1). It can be seen that the main growth period of rice root weight is from tillering stage to panicle differentiation stage. The post-anthesis root weight loss mainly occurs in 0-20cm tillage layer, and 65002 and Shanyou 63 decrease by 2162g and 0194g, respectively. However, the weight loss of the deep roots in the 20-45cm soil layer was relatively small (Table 1). The root volume per plant was increased in 2 plants per tube than in 1 plant.

With the progress of fertility, the proportion of deep roots (20~45cm) increases.

In the tillering stage, ear differentiation stage, flowering stage and maturity stage, the percentage of deep roots of 65002 were 6%, 1815%, 1911%, and 24%, respectively, and Shanyou 63 was 513%, 1912%, 2712%, and 2619%, respectively. The period of maximum root growth was from tillering to panicle differentiation.

3.2 Vertical Distribution Characteristics of Rice Roots

The vertical distribution of rice roots in different growth stages is shown in Fig. 1. The root systems of the tillering stage are mainly distributed in the surface soil of 0~10cm. There are few root systems below 10cm in the soil layer. In the panicle differentiation stage, flowering stage and maturity stage, 0~10cm The amount of roots was higher, and the differences were greater, and the amount of roots at the flowering stage was the largest. The amount of roots below 10 cm decreased gradually with the decline of the soil layer, and the difference was small. The amount of roots in the 40-45 cm soil layer was greater than 35-40 cm. Due to the depth of the tube, the roots continue to grow downward, causing the roots to pile up in this layer.

As can be seen from Figure 1, from the tillering stage to the panicle differentiation stage is an important period of root growth, so in the breeding and cultivation of ultra-high product species should pay attention to this period of root growth. Compared with Shanyou 63, the flowering phase of 65002 Large root growth (Table 1) is mainly manifested in the surface root (0~10cm) (Figure 1).

3.3 Effect of Soil Bulk Density on Root Growth

Soil compactness marked by soil bulk density affected the growth of roots. With the increase of soil bulk density, the growth of rice roots at flowering stage decreased. The root growth of 112g#cm-3 soil bulk density was 100% at 114g#cm-3 and 116g. The growth of 65002 roots under #cm-3 soil bulk density was 94% and 81%, respectively, decreased by 6% and 19%, and Shanyou 63 was 91% and 75%, respectively, decreased by 9% and 25% (Table 2).

Soil bulk density has a greater influence on the growth of deep root (20~45cm) than surface root (0~20cm). The soil bulk density of 112g#cm-3 is 100%. When soil bulk density is 114g#cm-3, 65002 and Shanyou 63 The surface roots were 93% and 103%, respectively, and the deep roots were 102% and 57%. When the soil bulk density was 116g#cm-3, the surface roots of 65002 and Shanyou 63 were 87% and 88%, respectively, and the deep roots were It is 57% and 37%. Therefore, when the soil bulk density increases, the weight of the deep root system decreases more, and the weight of the deep root system decreases to the total amount of the root system.

4 Discussion

4.1 Root Growth Dynamics

The root growth of rice was the largest in the flowering period, and some roots began to fall off after flowering. From the point of view of root biomass, roots that died after flowering mainly appeared in the topsoil, which may be the proportion of fine roots and root hairs in the roots of the surface. This part of the roots is easily shed in the later stages of death.

Although the upper part of the leaves after the flowering has gradually become senescent, especially the lower leaves, the total biomass above the ground has continued to increase, indicating that the root senescence is earlier than that of the above-ground organs, which is consistent with the phenomenon found on wheat.

4.2 Main periods of deep root formation

The period with the fastest growth of root biomass is from tillering to panicle differentiation. This period is also the main period of deep root formation. Since deep roots are closely related to yield, the regulation of tillering to panicle differentiation during super-high yield cultivation should be emphasized. Measures to promote root growth and downward growth. In the breeding of ultra-high-yielding varieties, the number of deep roots during panicle differentiation can be used as an important indicator for deep root selection.

4.3 Effect of Soil Bulk Density on Root Growth

This study showed that with the increase of soil bulk density, root growth decreased, which is basically consistent with previous research results. Under higher soil bulk density, the inhibition of deep root growth was greater than the surface roots, so the proportion of deep roots decreased. There is a difference between the combinations, 65002 in the soil bulk density of 114g#cm-3 when the soil 20~45cm root weight does not decrease. Deep roots expand the absorption surface of the root system in the soil, enhance the buffer against the adverse environmental conditions of the surface soil, delay the late Premature leaf defoliation. Differences in response of root growth to soil bulk density exist. Selection of a root growth-insensitive variety to soil bulk density may improve the adaptability of the variety to the soil environment.

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