بررسی تاثیر دو باکتری pseudomonas sp و enterobacter cloacae بر اشکال کربن خاک در کشت دو گیاه ذرت و گندم در ریشه‌دان (ریزوباکس)

به منظور بررسی تاثیر باکتری های محرک رشد بر برخی ویژگی‌های شیمیایی و بیولوژیکی خاک تحت کشت ذرت و گندم، آزمایشی در قالب طرح کاملاً تصادفی شامل دو گیاه ذرت و گندم و سه سطح مایه‌زنی شامل بدون باکتری، pseudomonas sp. strain rhizo_9 و enterobacter cloacae strain rhizo_33 در 3 تکرار در گلدان‌های تقسیم شده (ریزوباکس) و در شرایط گلخانه اجرا گردید. در پایان دوره کشت، گیاه برداشت و خاک های ریزوسفری1 (چسبیده به ریشه)، ریزوسفری2 (چسبیده به مش) وغیرریزوسفری (دور از مش) جدا و برخی ویژگی های خاک اندازه گیری شدند. نتایج نشان داد میزان هر یک از اجزاء کربن و همچنین تنفس پایه و برانگیخته در تیمارهای دارای باکتری بیشتر از شاهد و در خاک تحت کشت ذرت بیشتر ازخاک تحت کشت گندم بود. بیشترین میزان تنفس پایه میکروبی (31/0 میلی گرم co2 بر گرم بر روز)، تنفس برانگیخته (65/1 میلی گرم co2 بر گرم بر روز)، کربن قابل اکسید با پرمنگنات (1/213 میلی گرم بر کیلوگرم) و کربن زیتوده میکروبی (53/17 میلی گرم بر صد گرم) درخاک ریزوسفری1 در کشت ذرت مایه‌زنی شده با باکتری سودوموناس و بیشترین مقدار کربن آلی (82/0 درصد)، کربن محلول در آب سرد (1727 میلی گرم بر کیلوگرم) و کربن محلول در آب داغ (955 میلی‌گرم بر کیلوگرم) درخاک ریزوسفری1 در کشت ذرت مایه‌زنی شده با باکتری انتروباکتر به دست آمد که نشان‌دهنده تاثیر متفاوت دو باکتری بر افزایش اجزاء گوناگون کربن خاک می‌باشد. همچنین کاربرد هر دو باکتری موجب افزایش وزن خشک ریشه و اندام هوایی هر دو گیاه شد که در این میان تاثیر انتروباکتر بیشتر از سودوموناس بود.

The effect of pseudomonas sp and enterobacter cloacae on the distribution of carbon forms in the soil under corn and wheat cultivated in rhizobox

Introduction Growthstimulating bacteria are now proposed as an alternative to chemical fertilizers in order to increase soil fertility in sustainable agriculture. Biofertilizers are also expressed as microbial inoculants that are capable of removing soil nutrients from an inaccessible state through biological processes. Plant Growth Promoting Bacteria (PGPRs) refer to a broad group of susceptible bacteria, which grow alongside the plant as the host and stimulate plant growth. On the other hand, these microorganisms in the soil are able to stimulate and improve biological indicators, such as microbial carbon biomass, microbial respiration, and microbial yield, and may also affect different forms of carbon in the soil. Among the PGPRs, it is possible to refer to Enterobacter and Pseudomonas. Pseudomonas are bacteria present in all agrosoils and have different growthpromoting characteristics. Enterobacteriaceae family is a large group of bacteria that are naturally present in the water, soil, and materials that are corrupted and contaminated. To evaluate the biological changes of soil due to the activity of PGPRs, biochemical parameters (microbial respiration and microbial carbon biomass) are usually monitored in the plant’s rhizosphere. The rhizobox is one of the tools used to study the changes in the rhizosphere, by limiting the roots in a certain volume of soil and facilitating the sampling of rhizosphere soil. The aim of this study was to investigate the effect of plant growthpromoting bacteria on some biological and chemical properties of the soil under Rhizobox conditions. Materials and Methods In order to study some of the chemical and biological properties of the soil cultivated with maize and wheat and inoculated with growth promoting rhizobacteria (PGPR), a completely randomized design, including two maize and wheat plants and three levels of inoculation, including noninoculated, Pseudomonas sp. strain Rhizo_9 and Enterobacter cloacae strain Rhizo_33 in three replications in Rhizobox pots was done in greenhouse conditions. At the end of the period, the plants were harvested and the dry weight of roots and shoots was measured. Also, 3 soil samples were sampled from each rhizobox, as follows: rhizosphere 1 (soil clinging to the root), rhizosphere 2 (1 cm soil clinging to mesh), and nonrhizosphere (soil far from the mesh). Some soil characteristics, including basal respiration, substrate induced respiration, metabolic quotient, and soil carbon components (soil organic carbon, microbial carbon biomass, coldwatersoluble carbon, hotwatersoluble carbon, and permanganate oxidable carbon) were measured. Results and Discussion Results showed that the amount of each carbon component, as well as basal and substrateinduced respiration in treatments with bacteria, was higher than nonbacterial treatments and these biological properties in the soil cultivated with maize were higher than those under wheat cultivation. According to the results, the highest amounts of the basal respiration (0.31 mg CO2 g1 day1), the substrateinduced respiration (1.65 mg CO2 g1 day1), the permanganate oxidable carbon (213.1 mg kg1), and the microbial carbon biomass (17.53 mg 100g1) were related to rhizosphere 1 soil of maize inoculated with Pseudomonas. The highest amounts of the organic carbon (0.82%), the coldwatersoluble carbon (1727 mg kg 1), and the hotwatersoluble carbon (955 mg kg1) were related to rhizosphere 1 soil in maize inoculated with Enterobacter. This could show the differences between two bacteria in affecting on different forms of carbon in the soil. Conclusion The results of this study showed that maize had a higher effect on carbon forms of soil that could be because of higher root biomass and probably higher root secretions of maize in comparison to wheat. Also, by increasing the distance from plant roots (from rhizosphere1 soil to bulk soil), different forms of carbon decreased that showed the impact of rhizosphere (plant roots and rhizospheric microorganisms) on physicochemical and biological characteristics.Inoculation of PGPR bacteria caused an increase in soil respiration and soil different carbon forms but the two bacteria were different in increasing various forms of soil carbon that seems to be related to different secretions or different effects of bacteria or plantbacteria associate on soil carbon forms. Although inoculation of Pseudomonas resulted in a higher amount of microbial carbon biomass, inoculation of Enterobacter resulted in higher amounts of coldwatersoluble carbon, hotwatersoluble carbon, and soil organic carbon. Also, the application of two PGPR bacteria (Enterobacter was more effective) increased root and shoot dry weights of maize and wheat compared to nonbacterial treatments.