**2.1. Phosphorus and root signaling**

Among all essential plant nutrients, phosphorus (P) is the second most abundantly required nutrient element after nitrogen and is an important constituent of many structural components of the plants [19, 20]. In agricultural ecosystems, it determines the soil quality with respect to its production capacity [21]. Being scarce and non-renewable natural resource [22] which is under the threat of rapid depletion as a result of intensive mining across the world more emphasis is being given to increase P use efficiency in soil for successful and sustainable crop production. A field experiment was conducted over 2 years to study the ameliorating effects of P on wheat yield, root cation exchange capacity (CEC) and on different doses of P. Phosphorus was applied as single superphosphate. The application of P increased the root CEC of wheat up to bloom stage only whereas nutrient concentration, uptake and grain and straw yield were found to increase up to maturity [23]. The capacity of plant roots to increase their carboxylate exudation at low plant phosphorus (P) status is an adaptation to acquire sufficient P at low soil P availability. Root mass ratio decreased with increasing P supply for *Triticum aestivum* L. [24]. An experiment was set up to make a critical assessment of the role of organic P in soil solution in the nutrition of wheat plants under sterile conditions. Phosphorus supply had a positive effect on dry matter and P concentration of the plants. Acid phosphatase secretion by plant roots was 5–11 times higher in organic P treatments than in the inorganic P treatments. It was hypothesized that plants secrete phosphatases in response to the presence of organic P in soil solution and organic P might be responsible for the increase in P influx to wheat plants [25].

Root-soil contact is an important factor for uptake of a less mobile soil nutrient such as phosphorus (P) by crop plants. Root hairs can substantially increase root-soil contact. Identification of crop cultivars with more and longer root hairs can, therefore, be useful for increasing P uptake in low input agriculture. The variation in root hair parameters of the cultivars was related to quantity of P depleted from rhizosphere. These results showed that the variation in root hairs of cereal cultivars can be considerable and it can play a significant role in P acquisition, especially in low-P soils [26]. A field trial was conducted to investigate main morphological and physiological changes of different wheat landraces to low-P stress at the stage of seedling. P-deficiency significantly decreased root volume, total leaf area, and plant dry weight, but greatly increased density of root hairs and root top ratio. In addition, P-deficiency induced the significant enhancement of phosphorus utilization efficiency and the amount of proline, malondialdehyde, acid phosphatase, peroxidase and superoxide dismutase (SOD), but the significant reduction of P uptake and soluble protein content. The results based on the correlation analysis showed that the economic yield of wheat landraces had relationships with their morphological and physiological characteristics under P-deficiency [27].

availability of P [34], which also improves the P conversion in the internal of plant [35], by enhancing root-shoot ratio and root elongation releasing of organic acids or protons [36] and phosphatases [37]. The absorbed P by plant to produce more biomass is another adaptive mechanism to P deficiency in soil, thus low-P also limits the yield and quality of wheat [38], because P can effect on photosynthesis, photo-assimilate transportation and stunt growth of plant [39–41]. Further, the coupling effect of water and chemical fertilizers on different crops or varieties have been reported by many studies, they revealed that water and nutrient uptake were two physiological processes that interacted with each other [42–45]. Therefore, soil water content and P fertilizer, and meanwhile, their interaction plays great key role for crop growth [46], and suitable irrigation and fertilization is the main method to increase production. The effects of drought stress on the phosphorus (P), uptake dynamics throughout the growth cycle were studied. Drought stress induced sharp decreases in total P uptake at different developmental stages and, in particular, detrimentally affected the nutrient uptake capability of roots. The results suggested that plants differ in their ability to maintain nutrient uptake under drought stress, and it is highly dependent on the intensity and duration of drought stress and the developmental stage. The decrease in total P uptake caused by both moderate stress and severe stress was accompanied by reduction in biomass production in drought-stressed tissues. The biomass allocation patterns in response to drought stress fluctuated strong mostly because of competitive changes in the shoot and roots at different stages, thus the root: shoot ratio increased at some stages and decreased at other stages. Severe stress induced a dramatic reduction in the harvest index, whereas moderate stress slightly decreased harvest index. Thus, water limitation caused lower P uptake and harvest

Effect of Phosphorus on Root Signaling of Wheat under Different Water Regimes

http://dx.doi.org/10.5772/intechopen.75806

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The water content and nutrient in soil are two main determinant factors to crop yield and quality, managements of which in field are of great importance to maintain sustainable high yield. The objective of the study was to measure the uptake, forms, and use efficiency of phosphorus in wheat under irrigation. The results indicated that P fertilizer combined with irrigation not only improved the activity of phosphatase in soil, but also increased P accumulation in wheat, similar results was found in the grain of wheat, the content of total P increased significantly. The interaction between P and irrigation also significantly affected on the P accumulation, grain total P, grain phospholipids P, and P production efficiency [48].

Two experiments were carried out to study root signaling in response to different water regimes and level of phosphorus. First one was about screening of wheat genotypes for drought tolerance conducted in the laboratory. The sowing apparatus used was Petri dishes (9 cm diameter) in which 9 different varieties of wheat were sown under different level of PEG (polyethylene glycol) to induce stress. From these 9 varieties two varieties which gave better results under drought conditions were selected. These two varieties were further sown in the second experiment which was conducted in a polythene bags (2.5 feet long, 10 cm diameter). In the second experiment eight treatments were applied which were replicated thrice.

index [47].

**3. Materials and method**

The detail of both the experiments is given as under.
