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Free-living plant growth-promoting rhizobacteria (PGPR) have favourable effect on plant growth, tolerance against stresses and are considered as a promising alternative to inorganic fertilizer for promoting plant growth, yield and quality. PGPR colonize at the plant root, increase germination rates, promote root growth, yield, leaf area, chlorophyll content, nitrogen content, protein content, tolerance to drought, shoot and root weight, and delayed leaf senescence. Several important bacterial characteristics, such as biological nitrogen fixation, solubilization of inorganic phosphate and mineralization of organic phosphate, nutrient uptake, 1-aminocydopropane-1-carboxylic acid (ACC) deaminase activity and production of siderophores and phytohormones, can be assessed as plant growth promotion traits. By efficient use, PGPR is expected to contribute to agronomic efficiency, chiefly by decreasing costs and environmental pollution, by eliminating harmful chemicals. This review discusses various bacteria acting as PGPR, their genetic diversity, screening strategies, working principles, applications for wheat and future aspects in terms of efficiency, mechanisms and the desirable properties. The elucidation of the diverse mechanisms will enable microorganisms developing agriculture further.

Soil is the basis of agriculture and consists of organic matters, minerals, water, and several gasses. All plants require soil both as an anchor to attach and as water and nutrient source. Unfortunately, lifestyles of humans, industrial progress, chemicals used in agriculture contaminate soil and cause soil pollution. A pollutant may be natural or human-made in origin such as petroleum hydrocarbons, pesticides, heavy metals, and solvents. Since the quality of the soil affects the growth and product yield of plants, soil pollution is a crucial problem needs to be addressed urgently. Plant growth promoting rhizobacteria (PGPR) are microorganisms living in soil, on the plants roots, or inside the plant. PGPRs synthesize chemicals to stimulate plant growth and promote nutrient uptake, help degrading soil pollutants and fending off pathogens. While some pollutants can be degraded by enzymes produced by bacteria and fungi, degradation of heavy metals requires alternative methods. In this chapter, three enzymes produced by PGPRs are reviewed briefly. Aminocyclopropane-1-carboxylate (ACC) deaminase is responsible of lowering the ethylene levels of plants during stress conditions, whereas nitrogenase is responsible for N2 reduction to NH3. Moreover, phytase enables the degradation of phytate which is a main storage form of phosphate in plants.

Özet: Bu araştırmada Çayırhan Termik Santralı baca gazı emisyonlarının çevre toprakları üzerine yapmış olduğu etkiler araştırılmıştır. Bu amaçla emisyonların hakim rüzgar yönünde hareket edeceği göz önüne alınarak güney doğu yönünde bulunan tarım alanlarından 20 adet, kuzey doğu yönünden santral merkez kabul edilmek üzere Beypazarı ilçesine doğru 7 adet ve hakim rüzgar yönünün tersi istikameti olan kuzey batı yönünden de 3 adet toprak örneği 0-20 cm derinlikten alınmıştır. Toprak örneklerinin pH, organik madde ve toplam Pb, Cd, Ni ve S kapsamları belirlenmiştir.Kuzey doğu yönüne ait toprakların pH değerleri diğer yönlerin pH değerlerinden daha düşük olup, pH ile toplam kükürt, Cd ve Pb kapsamları arasında P<0.001 düzeyinde önemli negatif ilişki belirlenmiştir. Her üç yönden alınan toprakların toplam Pb ve Ni kapsamları Toprak Kirliliği Kontrol Yönetmeliği sınır değerlerinin altında bulunmuştur ve henüz yukarıda belirtilen metallerin kirliliğinden söz etmek mümkün değildir. Buna karşın, hakim rüzgar yönünden alınan toprakların toplam Cd değerleri hakim rüzgar yönü tersinden alınan topraklara nazaran oldukça yüksek ve Toprak Kirliliği Kontrol Yönetmeliği sınır değerlerinin üzerinde bulunmuştur. Benzer şekilde, kuzey doğu yönüne ait toprakların hepsinde ve güney doğu yönüne ait toprakların büyük çoğunluğunda S kirlenmesi ve hakim rüzgar yönü tersi olan kuzey batı yönünden alınan toprak örneklerinde de olası S kirlenmesi belirlenmiştir.Anahtar Kelimeler: Çayırhan, termik santral, emisyon, toprak, ağır metal, kükürt. Abstract:In this research, the effects of the emissions released by the Cayirhan Coal-Fired Power Plant on the soils were investigated. For this aim, taking into consideration that emissions would be transported in the prevailing wind direction, 20 soil samples from southwest fields, 7 samples from northwest fields in Beypazari township, 3 samples from northeast soils the position of which is in reverse direction to prevailing winds were taken at the depth of 0-20cm. Besides soil pH and organic matter contents, total Pb, Cd, Ni and S contents of the soil samples were also determined.pH values of the northwest soils were found to be lower than that of other soils and a significant negative correlation (P<0.001) was determined between total S, Cd and Pb contents.Total Pb and Ni contents of the soils of the three directions were found to be below the limits set out by the Soil Pollution Control Regulation. Therefore, metal contamination in these soils is out of question. Whereas, total Cd of the soils in the prevailing wind direction were observed to be considerably high in comparison with those in opposite wind direction, and to be above the limits of the regulation. Similarly, total S contamination was determined to be in the northwest and the majority of the southwest soils and the northeast soils of opposite direction to prevailing winds.

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