ارزیابی اثر فعالیت‌های کشاورزی بر تنوع و فراوانی باکتری‌های خاک‌زی

Among the biodiversity of soil microorganisms, bacteria have the basic role in soil functions. In order to determine the diversity and abundance of soil bacteria in arid regions, and also to study the effect of agricultural practices on them, a study was conducted in winter wheat fields on Shirvan, Mashhad and Gonabad. In each region, high and low input fields of winter wheat and a natural system for comparison were selected. Use of agricultural inputs was criteria for selection of low and high input fields in each region. Soil sampling was done on fields and natural systems and organic matter content, abundance and diversity of soil bacteria were measured in soil samples. Species richness and abundance of soil bacteria was affected by region and so that natural system of Gonabad has the minimum of species richness among the studied systems and the differences of other systems was not significant. Abundance of soil bacteria in 1 g dry soil was maximum in Gonabad and minimum in Shirvan. Abundance of soil bacteria was affected by organic matter and in low and high input systems of Gonabad and low input system of Mashhad was greater than other systems. Overall, 19 species of bacteria that belonged to 4 genus were detected. Results showed that species richness and abundance of soil bacteria in studied systems were relatively low and agricultural practices have not significant impact on these organisms, so that species richness and abundance of soil bacteria were improved in agricultural systems of Mashhad and Gonabad. Pattern of bacterial diversity showed that regional and agricultural stresses were affected on bacterial function so that in high level of stresses, species richness decreased and function of soil bacteria was restricted to decomposition of organic matter. Therefore, organic matter of soil must be increased and agricultural stresses must be decreased to improve of soil bacterial functions.