Journal of the Indian Society of Soil Science

Performance of the microbial community in seven forest soils viz. Lappwald (Lw), Zierenberg (Zb), Goettinger wald (Gw), Harste (Ha), Unterluess (Ul), Spanbeck (Sp) and Solling (So), along the acidity gradient (pH 5.7 to 3.7; base saturation 97 to 7%; Al³⁺ 2 to 83%) was assessed in terms of kinetics of added glucose, qCO₂, Cmic/Corg ratio, basal respiration, total adenylate content (TAC), adenylate energy charge (AEC) and microbial biomass as a case study to understand their relationship with changing microbial diversity. Microbial biomass (Cmic), TAC, Cmic/Corg decreased but qCO₂, increased with increasing acidity. Glucose-induced respiration followed a Michaelis-Menten kinetics. The Vmax decreased but the affinity of microorganisms for glucose increased (low Km) with increasing acidity. Both Vmax and Km were positively correlated with base saturation, Cmic, basal respiration, TAC, Cmic/Corg and negatively with qCO₂ and Al³⁺. The CO₂ evolution from Zb soil exponentially increased, 6 hours after addition of glucose but remained largely unchanged in Sp and Ha soils. In So soil, CO₂ evolution increased after 20 hours but the rate of increase was not exponential. On the basis of results, it is argued that with increasing soil acidity, microbial population of mild acidic base rich forest soils e.g. Zb, which utilize higher amount of available substrate by rapid multiplication gives way to a slow growing population adapted to low substrate availability e.g. Sp. Solling soil supported a mixed population of rapid and slow growing microorganisms, indicating a gradual shift in microbial diversity with increasing acidity. This shift in microbial diversity possibly took place along r-K continuum