Does cultivation influence the content and pattern of soil proteins?

Proteins comprise one of the largest N inputs to soils. There is, therefore, a need to investigate the factors involved in the inputs and fate of proteins in soil. While land use management is expected to influence the amount and diversity of soil proteins, the responses of protein as a source of mineralizable N to land use changes have not yet been studied. We hypothesized that extractable soil protein could be a sensitive indicator in evaluating the effect of stress in ecosystem. Soil samples were collected in October of 2009 from a native forest (Typic Calcixerolls) and a native rangeland (Typic Calcixerepts) as well as adjacent cultivated fields in Zagros area, central Iran. Tris–HCl buffer (pH 6.8) containing 1% (w/v) SDS was used for soil protein extraction. The results showed that soil protein content decreased by 64% and 55% in cultivated sites, as compared with their corresponding native forest and native rangeland sites, respectively. To determine the effects of land use changes on soil protein pattern, SDS-PAGE was carried out. Electrophoretic patterns of soil proteins from agricultural soils were clearly different from those of native lands. Protein bands ranged from 17 to 90 kDa and from 20 to 62 kDa in native forest and in the adjacent cultivated soils, respectively. Protein bands were detected in the range of 17–57 kDa for the native rangeland soil but in the range of 17–198 kDa for the adjacent cultivated soil. Land use changes were found not only to decrease significantly the amount of soil proteins but also to influence the protein pattern. We achieved the objective of this paper which was to show the potential of the quantity and diversity of soil proteins as indicators of land use changes. The presented soil protein extraction method as well as soil protein content and pattern determination require further validation in a variety of soils types, climates and land use systems.