CONTROL OF PLANTS OF LOTUS CORNICULATUS L. ON AEROBIC AND ANAEROBIC FREE NITROGEN-FIXING BACTERIA

Abstract

The free nitrogen fixing bacteria are able to mobilize important soil nutrients, transforming through biological processes the unusable molecular nitrogen into an active form and to improve soil fertility, influence many aspects of plant health and ensure their growth, showing interest for the scientific world and farmers. But, on the other hand, this bacterial segment may be influenced by the edaphic factors and the interconnection with the plants, the growth phase, the physiological state and the root system of the plant, by the root exudates, which demonstrates the importance of the bacterial community monitoring from the area of plants influence throughout the growing periods The aim of this study was to evaluate the influence of the age of the plants used as biofertilizer and soil moisture on the free nitrogen fixing bacterial communities (the genera Azotobacter and Clostridium) associated with the roots of the perennial plants of Lotus corniculatus L. There were two zones of interest, namely the area of influence of the roots of the plants (rhizosphere) but also the more distant area (edaphosphere). For the study of aerobic and anaerobic free nitrogen fixing bacteria soil samples were taken together with adjacent plants of Lotus corniculatus L. The experimental variants were located in the western part of Romania, the plants being cultivated on the same soil type, but on different plots, that were in the I-IV years of culture. The influence of Lotus corniculatus L. plants on the free nitrogen fixing bacteria has been reported in control experimental variants. Isolation and study of this bacterial group from the 8 experimental variants was performed on a specific mineral medium, favorable for the growth of the two bacterial genera. The results were evaluated after 5 and 10 days of incubation. Between the two assesments there were no noticeable differences in the nitrogen fixing bacterial community, except for the stimulatory effect observed in the control vatiant and rhizosphere of the first year culture. The plants influence on aerobic and anaerobic free nitrogen fixing bacteria was obvious in the II and IV years of the Lotus corniculatus L. culture, compared to the 76 control variants and varies substantially depending on the age of the plant. In most analyzed soil samples, both bacterial genera, Azotobacter and Clostridium were present, confirming the known ecological relation of unilateral advantage or passive stimulation of the aerobic bacteria compared to the anaerobic clostridia. Exceptions were the samples from the cultures of the first year (rhizosphere and control), but also the rhizosphere from the culture of the year II, where only anaerobic nitrogen fixing bacteria were detected. Our results suggested that plant-soil interactions exert control over the bacteria being studied.