Ko-Inokulation von Rhizobien (Ensifer meliloti) und Azospirillum : in vitro Effekte auf Luzerne (und ko-kultivierte Birken) und die mikrobiellen Gemeinschaften ihrer Rhizosphären in unterschiedlichen Böden

摘要

In the work „Co-inoculation of rhizobia (Ensifer meliloti) and Azospirillum: In vitro effects on alfalfa (and co-cultured birches) and the microbial communities of their rhizospheres in different soils“ it was examined, to what extent different inoculations affect the growth of alfalfa plants (Medicago sativa) and birches (Betula pendula) as well as their bacterial rhizosphere communities. The inoculations occurred with the nitrogen fixing bacterium Ensifer meliloti L33, with the plant growth promoting rhizobacterium Azospirillum brasilense Sp7 or with both bacteria. The effect of the inoculations was examined in different soils: A cropping soil and a soil contaminated with different metals as well as a mixture from both soils were used. The results showed that the used soil has an enormous effect on the growth of alfalfa plants. In the contaminated soil the plants only grew poorly. In the cropping soil they showed good growth and in the mixture of both soils they interestingly grew best of all. After six weeks, the tested inoculations also affected alfalfa growth, although only to a small extent and often not statistically significant. After 13 weeks the effects of the inoculations on alfalfa growth were even smaller than after 6 weeks. Because detection of both inoculants was less successful after 13 weeks than after 6 weeks, this result may be due to decreasing cell numbers or the complete disappearance of the inoculants. Altogether inoculation with A. brasilense Sp7 showed the best effects and inoculation with E. meliloti L33 the least ones. All three variations of inoculation showed a clearer positive effect in the cropping soil than in the other soils. This shows that not only alfalfa growth, but also the effect of an inoculation depends on soil type. The latter is probably explained in the fact that not every inoculant is able to survive in every soil. Thus A. brasilense Sp7 was not detected in any approach in the contaminated soil and E. meliloti L33 was not detected in the soil mixture. This may be an explanation for the small effects on alfalfa plants. Consequently, the choice of a suitable soil is of great importance for alfalfa growth and growth deficits caused by an inapplicable soil can be decreased only to a small extent by an inoculation. Hence, before planting and inoculation of agricultural areas it is recommendable to test whether the plant to be cultivated manages with the soil, whether the desired inoculant is able to survive in the concerning soil and to what extent it is able to promote the growth of this plant in the special soil. The growth of the birches did not change significantly because of the inoculations, neither after 6 nor after 13 weeks. Maybe test duration of this work was too short for the slowly growing wooden plant. An other possibility is that the inoculants used here have generally no effect on birch growth. From ecological view inoculation of agricultural areas with the bacteria used here seems to be rather safe. The inoculations did not influence the whole bacterial community of the rhizospheres measurable and the active community only slightly.