Short-term changes in microbial biomass and activity in soils under black locust trees (Robinia pseudoacacia L.) in the northwest of Turkey

The literature indicates that the presence and activity of microbial biomass could be potential indicators of other changes in mineral soils, making it useful for monitoring and assessing the relationships between plants and soil and their effects on the health and quality of the soil. Therefore, the aim of the study was to determine whether if there were any changes in the C and N content or the basal respiration of microbial biomass in soils under black locust trees (Robinia pseudoacacia L.) between 2013 and 2014. Samples of topsoil (0-6.5 cm) under the black locust were collected randomly from 12 different locations in 2013, and 12 samples were taken from the same locations in 2014. The C and N contents of the microbial biomass were determined by the chloroform fumigation extraction method. Basal respiration was determined by the sodium hydroxide (NaOH) trap method. The results demonstrated that the average C content of microbial biomass (C-mic) increased by about 55 % in soils under black locust and that the average N content (N-mic) of microbial biomass N increased by about 59 %. Both the C-mic and N-mic values were significantly affected by the temporal variation (P < 0.05). The average basal respiration was lower in 2013 than in 2014, i.e., 0.303 and 0.526 mu g CO2-C g(-1) h(-1), respectively; this difference from 2013 to 2014 was statistically significant (P < 0.05). Related to substrate (glucose, protein, carbohydrate, etc.) quality, the average C-mic/C-org (%) of the soils was significantly (P < 0.05) lower in 2013 (5.18 %) than in 2014 (6.86 %). Similarly, the metabolic quotient (qCO(2)), on average, also was lower in 2013 (0.96 mg CO2-C g(-1) C-mic h(-1)) than in 2014 (1.10 mg CO2-C g(-1) C-mic h(-1)); however, the difference in the values for the two years was not statistically significant (P > 0.05). Thus, it was concluded that the effect of black locust on the C and N content and basal respiration of the microbial biomass was due to the combined result of changing microclimatic conditions and soil characteristics, including the temperature, moisture content, pH, organic C, and total N in the soil. Therefore, this tree is an appropriate and valuable species where poor ecological conditions exist because of its rapid growth rate and its positive effect on the health and quality of soil.