Effect of water stress on the density of rhizospheric fungi, Actinomycetes and Azotobacters associated with cereal cultivation
H. Marouane, K. Oulbachir, K. Acem
The study evaluates the effect of water stress on the microorganisms biomass of the rhizosphere associated with cereal cultivation. The latter selects the most resistant germs to introduce them into the improvement of the system: soil-plant under water stress condition. The study of the effect of water deficit on the rhizospheric microbial biomass under a cereal crop (durum wheat) in situ reveals a reduction in the density of Actinomycetes, Azotobacters, and fungi. First, concerning the cultivated soil subjected to rainfall, the number of Actinomycetes gradually decreases from 25.5.106 germs/g to 3.33.106 germs/g. Whereas the cultivated soil irrigated at 50% to the field capacity, their number also decreases from 43.106 germs/g to 3.9.106 germs/g. The cultivated soil is irrigated at 100% to its field capacity; the density gradually decreases from 210.106 germs/g to 5.76.106 germs/g. Similarly, in the cultivated soil subjected to rainfall, the Azotobacters rate gradually decreases from 36 .106 germs/g to 10.7.106 germs/g. Regarding the cultivated soil irrigated at 50% to field capacity, the density gradually decreases from 91.106 germs/g to 5.03.106 germs/g. In the cultivated soil that was 100% irrigated to the field capacity, the density gradually decreases from 1.3.106 germs/g to 2.106 germs/g. This reduction is achieved under humidity values close to the wilting point of loamy, sandy soil. The highest values were recorded at the vegetative stage: tillering. The study revealed that the effect of water stress on the evolution of fungi is less significant. There is a correlation between their density and some pedoclimatic parameters, which vary under water stress, such as the pH of the studied soil. It has been recorded that Actinomycetes were the least sensitive to water stress, unlike Azotobacters. Hence, they can be the most valuable microorganisms as auxiliaries for improving plant production, namely PGPR (Plant Growth Promoting Rhizobacteria).