| Abstract: | Abstract We studied the effects of the application of organic matter (OM) and chemical fertilizer (CF) on soil alkaline phosphatase (ALP) activity and ALP-harboring bacterial communities in the rhizosphere and bulk soil in an experimental lettuce field in Hokkaido, Japan. The ALP activity was higher in soils with OM than in soils with CF, and activity was higher in the rhizosphere for OM than in the bulk soil. Biomass P and available P in the soil were positively related to the ALP activity of the soil. As a result, the P concentration of lettuce was higher in OM soil than in CF soil. We analyzed the ALP-harboring bacterial communities using polymerase chain reaction based denaturing gradient gel electrophoresis (DGGE) on the ALP genes. Numerous ALP genes were detected in the DGGE profile, regardless of sampling time, fertilizer treatment or sampled soil area, which indicated a large diversity in ALP-harboring bacteria in the soil. Several ALP gene fragments were closely related to the ALP genes of Mesorhizobium loti and Pseudomonas fluorescens. The community structures of the ALP-harboring bacteria were assessed using principal component analysis of the DGGE profiles. Fertilizer treatment and sampled soil area significantly affected the community structures of ALP-harboring bacteria. As the DGGE bands contributing to the principal component were different from sampling time, it is suggested that the major bacteria harboring the ALP gene shifted. Furthermore, there was, in part, a significant correlation between ALP activity and the community structure of the ALP-harboring bacteria. These results raise the possibility that different ALP-harboring bacteria release different amounts and/or activity of ALP, and that the structure of ALP-harboring bacterial communities may play a major role in determining overall soil ALP activity. |
