| Plant root, as an important organs absorbing water and nutrients and synthesizing growth regulation, have a direct influence on the crop growth and yield. Roots play a remarkable role in dryland agriculture with serious soil water restriction. Because of the difficulty in separating root techniques, the studies involved plant root system have not been deepened as against the studies of plant aboveground. Micro-plot field experiment was conducted under rain-proof shelter for studying the relationship to root physiological characteristics and nutrient uptake of crop, plant growth, with different N and water supply under different cultivating measures. The results are shown as follows:1. The effects of N on root physiological characteristics, nutrient uptake, photosynthesis and plant growth were limited by water supply. When water supply was relatively sufficient (irrigated water) or slightly stressed (non-irrigated water and grown naturally), N supply stimulated root growth development, increased total absorbing area, actively absorbing area and TTC reductive amounts of roots, raised the bleeding sap amounts and the contents of NOs", NH4+, free amino acid, P and K in the sap, promoted the nutrient uptake of root, improved the physiological characteristics of photosynthesis, and consequently resulted in increasing crop yields and easing the harmful effects of restricting root growth. In contrast, when water was seriously stressed (non-irrigated water and non-mulching and grown naturally), input of N did not only decline the root growth biomass, root absorbing area and TTC reductive amount of root but also decreased the bleeding sap amounts and the content of NOs", NH/, free amino acid, P and K in the sap, reduced the nutrient uptake, inhibited the stomatal factors and the non-stomatal factors of photosynthesis, decreased the photosynthesis rates, therefore, this reduced nutrient absorbing amounts and crop yields, aggravated the harmful effects of restricting root growth.2. Although restricting root growth seriously inhibited the root development, it increased root actively absorbing area and improved TTC reductive intensity of root. Under the natural growth condition, the root actively absorbing area and TTC reductive intensity closely related to the nutrient uptake and aboveground biomass during crop vigorous growth stages. It showed that crop did not passively suffer stress, but initiatively adjust its physiological metabolism processes, strengthened its absorbing ability to water and nutrients, reduced the injure of root with the stressed environment. Being early consumed water and nutrient in the nylon bags, root could not go through nylon bags, and not assimilate the water and nutrients, hence the improvement of root inherent adsorptive ability can not change the decrease of nutrient uptake amounts and yields.3. Under the condition of different water and N supply, the trend was almost same for N, P and K uptake of crop and bleeding sap amount as well as nutrients in sap, the amounts of taking up N, P, K had remarkable positive correlation with the nutrients in bleeding sap. The results strongly suggested that the bleeding sap was not only the indication of plantgrowth vigor, but also the capacity of plant absorbing, and transferring water and nutrients.4. The total dry matter of maize and N, P, K uptake amounts were continuously increased with plant growth, and the dynamics of its change could be described by S-curve equations. The dry matter accumulation and nutrient uptake was not in the same rate at all time, the rate was increased fast at early stage, and gradually decreased after reaching their peak. Of N, P and K, the uptake rate for N and K was higher, and their increase and decrease were both fast while P was in reverse case. The time for maximum absorbing rate appeared earlier for K, followed by N, then by P. In any case, the time for maximum nutrient uptake rate appeared earlier than did the dry matter. The N recovery rate was similar in trend to those of dry mat...
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