Study on Dynamic Changes of Wheat Root System Parameters

Study on Dynamic Changes of Wheat Root System Parameters

1 Dynamic changes of wheat root length

The length and thickness of crop roots are very important for crops to absorb nutrients and water. At present, domestic root analyzers are commonly used to measure various parameters of root systems. Studies have shown that the absorption of nutrients by crops does not depend entirely on the weight of roots, but mainly on root length and root surface area. The root length of single wheat is highly affected by the water and fertilizer conditions in the soil and other environmental conditions, especially on soils. The response to moisture is more sensitive. When the soil is severely drought (40% of soil relative water content), the elongation of the roots is seriously impeded. When the soil moisture is good, the root length is significantly increased. When the relative soil moisture content is about 55%, the root system is the longest.

Many experiments have shown that fertilization can promote the growth of crop roots, thereby promoting the absorption and utilization of deep soil moisture by crops. The effect of P nutrition on root length varies with soil moisture status. Under severe water shortage conditions, P application has an extremely significant effect on the promotion of root growth. Subsequently, soil fertility decreases with increasing soil moisture content; Fertilizer can not only increase the number of roots in the upper layer, but also can promote root barbulation, increase root length and root number, enhance crop water absorption and improve drought resistance, and P fertilizer has greater influence on root length than N fertilizer. Studies have shown that the length of wheat roots is not sensitive to the response of N fertilizer. With the increase of soil moisture, the effect of N fertilizer on root length is gradually weakened.

Cultivation measures also have a significant impact on the growth and vigor of wheat roots. Deep plowing to break the bottom of the plow is beneficial to improve the permeability of the soil, increase the ability to store water and soil moisture, and promote the roots to lower the shoots; moderate drought at the seedling stage can also promote the roots to lower the bark; the number of secondary roots per plant decreases with the increase of the density. The number of rooting increases with the density. Plastic film mulching helps to promote early root growth, increase root length, root number and root weight, improve the distribution of roots in the soil, and is conducive to prolonging the absorption function of part of the root system during the later period of crop growth. Film mulching improved the soil environment in wheat fields and significantly promoted root growth. According to reports, the roots covered with wheat were (5.08±0.64), and the open field wheat was (3.79±0.43); the number of secondary roots of plastic film wheat was 10.6, and that of exposed wheat was 7.2, and the difference was extremely significant.

2 Dynamic changes of wheat root weight

It is generally believed that the number and weight of wheat roots increase with the occurrence of tillers. The number of wheat roots is the highest in the highest tiller period, and the total weight of roots before and after heading is the largest, and the roots gradually die after heading, and the root volume decreases, but the root system The activity has remained until the end. The distribution of root system in the soil is consistent with the distribution area of ​​available phosphorus in the soil. 80% of the root system is distributed in the soil tillage layer. The effect of soil moisture on the dry weight of wheat roots is obvious. When the soil relative water content is 40%, the wheat roots are seriously obstructed and the root dry weight is significantly reduced. When the relative soil moisture content is between 55% and 61%, the root dry weight is the greatest. Afterwards, the greater the relative soil moisture content, the significantly lower the root dry weight. It shows that the relationship between root weight and water use efficiency is very close.

The effects of N and P fertilizers on root dry weight have a great relationship with soil moisture. The results showed that the appropriate application of N (276kg/hm2) can increase the total root weight and root weight in deep soil, which helps to improve the drought resistance of wheat. Over-application of N (690kg/hm2) can increase the root weight of the upper layer. However, when soil moisture is seriously deficient, the application of N fertilizer is unfavorable for improving the dry weight of wheat roots. Increasing P fertilizer can significantly increase the root dry weight, but under different water conditions, the appropriate amount needed for P to promote root weight growth is different. The effect of P fertilizer on root dry weight was also related to the location of its application, and the effect of P was most significant when the soil was severely droughty (the soil relative water content was 40%). N and P interactions have a significant effect on root dry weight. When one of the N and P elements in the soil is maintained at a higher level, lowering the other element will increase the root to shoot ratio, that is, when the soil is unbalanced with N and P. Root-to-crown ratios will be affected, and root growth will increase relatively. Combined application of organic and inorganic fertilizers can increase the root dry weight of winter wheat, especially the root dry weight of 40-100 cm soil layer. The covering of winter wheat is conducive to the increase of root weight and the lower roots, absorbing the water in the lower layer and reaching the root water transfer. The root weight of mulched wheat in the same soil moisture treatment was increased by 30.3%~48.6% compared with the control, and the distribution was deeper.

3 Wheat Root Surface Area and Root Activity

Under field conditions, the strength of root absorption activity not only depends on the spatial distribution of root absorption activity, but more importantly, it depends on the level of root activity in the unit soil, and the increase and decrease of the root absorption activity of field winter wheat in the horizontal direction. The changes in the order from near to far and from top to bottom in the vertical direction and from inside to outside in the entire soil space finally show the complete decline of the vitality of the entire root system. The spatial expansion of root absorption activity is consistent with the scope of morphogenesis of the root system. After the annual deep roots of winter wheat increase after flowering, there are some aging roots in the upper layer of soil. Secondly, the water deficit during the flowering period will cause the decline of root activity and premature aging, which will directly affect the grain yield. The lack of water in the early period will affect the size of the vegetative body, and will have little effect on the yield. The lack of water during the grain filling stage will result in the dry matter stored in the stalk and reduce the Grain to stem ratio and harvest index. When the soil relative water content is above 70%, with the increase of P level, the root respiration increases; when the soil relative water content is below 55%, with the increase of P level, the root respiration is weakened. The effect of N on the respiration of roots is that when the relative soil water content is 40% to 70%, the respiratory intensity of the high N level root system is always higher than that of the low N level, and regardless of the level of N, the respiratory intensity under the condition of soil water shortage It is always higher than the breathing intensity under high water conditions.

The activity of wheat roots is greatly affected by cultivation measures. Sparse planting can increase root vigor and promote deeper distribution. In autumn, 1 to 2 years old tillage is used to promote root growth and improve root activity in deep soil. Increase wheat production. Soil moisture conditions have a dramatic effect on the surface area of ​​the root system and are parabolically distributed. Under different levels of P nutrition, the effects of soil moisture on root surface area were different: under the condition of no application of P, the root surface area peaked when the soil relative water content was 57%; when the P level was 90 kg/hm2, soil contained relatively The surface area of ​​the root system was the largest when the water amount was 54%. When the P level reached 180kg/hm2, the root surface area reached the maximum value when the relative soil water content was 51%. This shows that P fertilizer can significantly increase the active absorption area of ​​the root system. Therefore, adjusting the application amount of N and P fertilizer based on soil moisture can promote the expansion of wheat root surface area. Organic fertilizer can stimulate the activity of wheat roots, thus changing the absorption characteristics of phosphorus in the root system and increasing the absorption of phosphorus. But the effect of using organic fertilizer is short, and the application of organic and inorganic fertilizers can maintain this effect for a long time. , Can effectively reduce the root membrane lipid peroxidation, enhance root activity; different periods of fertilization of water has a short-term effect on root activity, jointing fertilizer and water and booting stage fertilizer can improve the root activity of the late, delay leaf senescence, and promote grain weight increase.

4 Changes of Spatial Distribution of Wheat Root System

Reports on the dynamic changes of the spatial distribution of wheat roots vary according to the object of study. The vertical distribution of maximum root biomass at the heading stage of winter wheat in dryland was about 85% in the 0-20 cm topsoil layer, the root weight in the 20 to 100 cm soil layer was reduced to 7.7%, the root weight in the 100 to 200 cm was 2.9%, and the total root system was less than 200 cm in the marginal layer. About 4.4%. Whether root length or root weight of winter wheat in watershed, 80% are distributed in 0~50cm soil layer, and the root system below 100cm is less than 6% of total root coefficient. For different drought-resistant winter wheat varieties, heading The results of the vertical distribution of the root system showed that the root dry weight decreased with the increase of the subterranean zone, ie 0-15cm>15-30cm>30cm; the proportion of the root dry weight of the drought-resistant varieties increased. The vertical distribution of wheat root system regardless of quantity or biomass (root weight, root length, root surface area, root volume) shows a decreasing exponential function (y=A・e-BX, where -B is the degressive rate, which determines the root distribution Important parameters; A is the maximum value; the percentage of cumulative root weight, root length in each layer of soil with the relative depth is in accordance with the hyperbolic function; the total root length and total dry weight change with time is Logsitic curve and optimal The growth curve of the number of wheat roots is a cubic polynomial.

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