Functional diversity of culturable bacterial communities in the rhizosphere in relation to fine-root and soil parameters in alder stands on forest, abandoned agricultural, and oil-shale mining areas

Grey alder ( Alnus incana) and black alder ( Alnus glutinosa) stands on forest land, abandoned agricultural, and reclaimed oil- shale mining areas were investigated with the aim of analysing the functional diversity and activity of microbial communities in the soil - root interface and in the bulk soil in relation to. fine- root parameters, alder species, and soil type. Biolog Ecoplates were used to determine community- level physiological profiles ( CLPP) of culturable bacteria in soil - root interface and bulk soil samples. CLPP were summarized as AWCD ( average well color development, OD 48 h(-1)) and by Shannon diversity index, which varied between 4.3 and 4.6 for soil - root interface. The soil - root interface/ bulk soil ratio of AWCD was estimated. Substrate- induced respiration ( SIR) and basal respiration ( BAS) of bulk soil samples were measured and metabolic quotient ( Q= BAS/ SIR) was calculated. SIR and Q varied from 0.24 to 2.89 mg C g(-1) and from 0.12 to 0.51, respectively. Short- root morphological studies were carried out by WinRHIZO TM Pro 2003b; mean specific root area ( SRA) varied for grey alder and black alder from 69 to 103 and from 54 to 155 m 2 kg) 1, respectively. The greatest differences between AWCD values of culturable bacterial communities in soil - root interface and bulk soil were found for the young alder stands on oil- shale mining spoil and on abandoned agricultural land. Soil - root interface/ bulk soil AWCD ratio, ratio for Shannon diversity indices, and SRA were positively correlated. Foliar assimilation efficiency ( FOE) was negatively correlated with soil - root interface/ bulk soil AWCD ratio. The impact of soil and alder species on short-root morphology was significant; short- root tip volume and mass were greater for black alder than grey alder. For the investigated microbiological characteristics, no alder- species- related di. erences were revealed.