Partial root regulation of plant water and nitrogen uptake

Fertilizer is generally only applied to the plowed soil and the sub-soil usually contains less fertilizer. How can plants grow normally under such conditions? In this paper, I present a hypothesis dealing with the uptake of water and nutrients by plant roots from soils that have different nutrient concentrations. The hypothesis is that roots partially control solution absorption. To test this hypothesis I used tomato plants with two root systems A and B. Treatments consisted of growing the plants in different combinations of nutrient solutions of varying concentrations. The solution uptake of a more dilute concentration by root system A increased as the nutrient concentration of root system B increased. When all the roots were supplied with concentrated nutrient solutions, the plants excessively absorbed nitrogen. However, when root system A was supplied a dilute solution, the nitrogen uptakes from root system B decreased. This show that roots supplied with a dilute solution prevent a plant from excessive nitrogen uptake. Root weight of root system A supplied with water did not increase in plants of root system B supplied with nutrient solution, in spite of a great increase in leaf area. However, root weight increased in plants supplied with only water. In a plant of which root system A and B were supplied with respectively a water and nutrient solution, the carbohydrate produced in the leaves is probably transferred into root system B. For partial root regulation of water and nutrient uptake, not only water and carbohydrates but also some amount of nutrients in water including root system A are probably needed.