كليدواژه :
بلندي گياه , پتاسيم نامحلول , مسكويت , ورمي كوليت , وزن خشك
چكيده فارسي :
هواديدگي كاني هاي خاك، خاستگاه بسياري از عناصر غذايي ضروري رشد گياه مانند پتاسيم هستند. كاني هاي ميكايي خاستگاه اصلي برآورد پتاسيم در خاك هاي كشورمان هستند. اين پژوهش با هدف جداسازي باكتري هاي حل كننده پتاسيم از ريزوسفر گندم و بررسي توانايي اين باكتريها در بهره گيري از پتاسيم ساختاري كاني هاي مسكوويت و ورمي كوليت انجام شد. اين پژوهش در زيستگاه درون شيشه اي با آرايش فاكتوريل در قالب طرح كاملا تصادفي در 3 تكرار انجام شد. فاكتورهاي آزمايش سه سطح باكتري (شاهد بدون مايه زني، و مايه زني با باكتري 1 و 2) و چهار گونه تيمار كاني پتاسيم (مسكويت، ورميكوليت، مسكويت K2HPO4+، ورميكوليت K2HPO4+) بود. در پايان دوره كشت، بخش هوايي گياه برداشت و به روش خاكستر خشك پتاسيم آن به كمك فروغ سنج اندازه گيري شد. همچنين صفات وزن تر و خشك اندام هوايي و ريشه، بلندي گياه و درازي ريشه اندازه گيري شد. اين بررسي نشان داد كه پيامد مايه زني دو باكتري برهمه ويژگي هاي اندازه گيري شده در سطح يك درصد معني دار است. همه ويژگي هاي ياد شده در بودن Bacillus subtilis و كاني ورمي كوليت بالاترين اندازه ها را داشتند. اندازه پتاسيم جذب شده در گياه به گونه معني داري وابسته به بستر كشت گياه بود. اندازه پتاسيم جذب شده در گياه، در سطح يك درصد به گونه معني داري وابسته به باكتري حل كننده پتاسيم بود. بيش ترين غلظت پتاسيم اندام هوايي (0.062 درصد) در تيمار بستر ورمي كوليت به همراه پتاسيم محلول در بودن Bacillus subtilis بود. بيشترين اندازه جذب پتاسيم در اندام هوايي گياه (0.049 ميلي گرم در گلدان) نيز در بستر ورمي كوليت به همراه پتاسيم محلول در بودن Bacillus subtilis و پس از آن در اندام هوايي گياه (0.036 ميلي گرم در گلدان) كشت شده در بستر مسكويت به همراه پتاسيم محلول در بودن Bacillus subtilis با اختلاف معني دار در سطح 5 درصد اندازه گيري شد.
چكيده لاتين :
Introduction: Potassium (K) is the third major essential macronutrient for plant growth. Without adequate
potassium, the plants will have poorly developed roots, grow slowly, produce small seeds and have lower yields.
Due to imbalanced fertilizer application, potassium deficiency is becoming one of the major constraints in crop
production. The concentrations of soluble potassium in the soil are usually very low and more than 90% of
potassium in the soil exists in the form of insoluble rocks and silicate minerals. Soil microbes have been reported
to play a key role in the natural K cycle and therefore, potassium solubilizing microorganisms present in the soil
could provide an alternative technology to make potassium available for uptake by plants. Thus, identification of
microbial strains capable of solubilizing potassium minerals quickly can conserve our existing resources and
avoid environmental pollution hazards caused by heavy application of chemical fertilizers.
Materials and Methods: This study aimed to isolate and identified potassium solubilizing bacteria and
evaluate those effect on K availability from muscovite and vermiculite sources to wheat crop under in vitro
condition. The study was conducted as factorial in completely randomized design at three replications included
bacterium inoculation (control, isolate1, isolate 2) and four k sources (muscovite, vermiculite, muscovite+
K2HPO4, vermiculite+ K2HPO4). Bacterial isolates were obtained from wheat rhizosphere on modified
Aleksandrov medium containing muscovite and vermiculite powder as potassium source. Nutrient broth medium
was used to prepare an overnight culture of bacteria to inoculate in Aleksandrov medium, which was used to
study the dissolution of silicate minerals. The zone of solubilization recorded on Aleksandrov medium. Then the
ability of two bacterial strains, including Bacillus subtilis and Corynebacterium glutamicum to release mineral K
from muscovite and vermiculite was investigated. After 18 days of seed culture, aerial part of plant growth was
dry digested and K concentration was determined by flame photometry. Dry and fresh weight of aerial part and
root, plant height and root length was recorded.
Results: Three K-solubilizing isolates from 15 isolates identified by biochemical and molecular methods
which belonged to Bacillus subtilis, Pseudomonas putida and Corynebacterium glutamicum. The potassium
solubilization zone of each strain on Aleksandrov medium containing muscovite were 8.1, 65.1 and 6.3,
respectively. The zone was also 9, 8 and 5.8 in Aleksandrov medium in the presence of vermiculite as insoluble
potassium source. According to these results potassium release from vermiculite was more than muscovite, in
spite of more potassium content of muscovite. According to the obtained results two strains Bacillus subtilis and
Corynebacterium glutamicum were selected for in vitro experiment because of halo to colony diameter ratio. The
ratio of halo to colony diameter in the presence of muscovite for Bacillus subtilis, Pseudomonas putida and
Corynebacterium glutamicum was 1.5, 0.72 and1.3, respectively. These ratios were 2, 1.4 and 0.8, respectively
in the medium containing vermiculite as insoluble potassium source. The results showed that the effect of
bacteria inoculation was significant (p<0.01) on all measured parameters. After being treated with the each of
KSB strains, plant dry weight and uptake of K by wheat seedlings increased significantly. These increases were
higher with the combination of Bacillus subtilis inoculation and vermiculite powder addition. Potassium
concentration of plant was depended to culture medium. Maximum K solubilization occurred when vermiculite
was used as a potassium source followed by K2HPO4. Also K concentration of plants was significantly (p<0.05)
affected by bacteria. In our study Bacillus subtilis showed the most pronounced beneficial effect on plant growth
and K concentration by wheat seedlings. There was significant difference between potassium concentration in
aerial part of wheat seedling cultivated in bacteria free medium with soluble potassium and medium containing
bacteria without soluble potassium. This results shows the importance of potassium solubilizing bacteria to
supply potassium for plant.
Discussion and Conclusion: The enhanced release of mineral K might be attributed to the release of organic
acids from the bacteria, a mechanism which plays a pivotal role in solubilizing potassium from inorganic source
of potassium. According to the results combining the inoculation of potassium solubilizing bacteria and the
addition of K bearing minerals could be a promising sustainable alternative to commercial K fertilizer and may
help maintain the availability of soil nutrients. Further studies are necessary to determine the effects of these
bacterial strains on mobilization of potassium-bearing minerals under field conditions.
