Study the Effect of Different Phosphorus Fertilizers on Physiological Characteristic of Photosynthetic Pigments and Soluble Sugars of Safflower under Water Deficit Condition

Drought stress is one of the most important and effective factors in agricultural practices in arid and semi-arid regions of the world. The arid and semi-arid regions comprise more than 70% of the total area of Iran. Reduction in chlorophyll concentrations has been attributed to the increase in chlorophyll degradation in water deficit conditions and impairment in the enzymes activity responsible for the synthesis of photosynthetic pigments. Under drought stress, maintenance of photosynthetic capacities and leaf chlorophyll are physiological parameters which influence drought stress tolerant of crop. Phosphorus is one the most essential elements for plant growth after nitrogen. However, the availability of this nutrient for plants is limited by different chemical reactions especially in arid and semi-arid soils. Plant growth-promoting bacteria (PGPB) are soil and rhizosphere bacteria that can benefit plant growth by different mechanisms. Given the negative environmental impact of chemical fertilizers and their increasing costs, the use of PGPB as natural fertilizers is advantageous for the development of sustainable agriculture. Inoculation of plants with native beneficial microorganisms may increase drought tolerance of plants growing in arid or semi-arid areas.
In order to study the effect of biologic and chemical phosphorous fertilizer on photosynthetic pigments of safflower cultivar (IL111), under water deficit condition, an experiment was conducted in 2012 at the Research Field of the Faculty of Agriculture, Shahed University. The experimental design was split-factorial arrangement in randomized complete block design with three replicates. The main factors were the three levels of irrigation treatment: full irrigation (irrigation up to 50% soil moisture depletion relative to field capacity), water stress in the vegetative and flowering stages (irrigation up to 75% soil moisture depletion relative to field capacity). The sub-factors were the six treatments resulting from three levels of phosphate chemical fertilizer (0, 50, and 100 kg ha-1 Triple Super Phosphate), each at two levels of Barvar-2 bio-fertilizer (with and without inoculation with Barvar-2). The applied biological fertilizer was in the type of the bacteria which release the phosphorus from soil components and neutralize the soil pH. The commercial name of the biologic fertilizer is Barvar-2. The effective gradients of the biological phosphorus fertilizer is comprised of two bacteria strains of p5 (Bacillus lentus) and p13 (Pseudomonas potida) with 108 cfu (colony forming units) which have been screened from soil bacteria populations. The bacteria strain p5 (Bacillus lentus) dissolves P from soil mineral compounds while p13 (Pseudomonas potida) separates P from soil organic compounds by exerting a variety of phosphatase enzymes.
The results showed that the highest amount of chlorophyll a, b and total chlorophyll obtained with application of chemical phosphorus by 100 kg ha-1 Triple Super Phosphate followed by inoculation with Barvar-2 under water deficit condition at vegetation and flowering stages. At drought stress in flowering stage, use of high level of phosphorus without inoculation with Barvar-2, had highest effect in terms of increasing amount of chlorophyll a/b ratio, but at treatment of inoculation with Barvar-2, the highest amount of chlorophyll a/ b ratio obtained with low level of chemical phosphorus by 50 kg ha-1 Triple Super Phosphate. The means comparison showed that highest amount of carotenoids, fv/fm, anthocyanin, flavonoids and soluble sugars obtained with application of chemical phosphorus by 50 kg ha-1 Triple Super Phosphate without Barvar-2 under water stress condition at vegetation and flowering stages. The inoculation with Barvar-2 followed by chemical phosphorus by 50 kg ha-1 Triple Super Phosphate significantly increased the amount of anthocyanin and soluble sugars of leaf under drought stress at flowering stage, while the amount of carotenoids and flavonoids, increased with Barvar-2 without using of chemical phosphorus.
Our experiment showed that application of chemical phosphorus fertilizer followed by inoculation with Barvar-2 had huge effect on chlorophyll a, chlorophyll b, total chlorophyll, chlorophyll a/ b, carotenoids, fv/fm, anthocyanin, flavonoids and soluble sugars under water stress condition at vegetation and flowering stages. The highest amount of photosynthetic pigment such as anthocyanin, flavonoids, carotenoids and soluble sugars could increases stress tolerance of safflower under water deficit condition. In general, the results of this experiment showed that application of Barvar-2 followed by chemical phosphorus had effective role in improve of qualitative traits of safflower under drought stress condition.