Temporal variations of the distribution of water-stable aggregates, microbial biomass and ergosterol in temperate grassland soils with different cultivation histories

- Microbial and fungal biomass increased in the first year after establishing grassland.
- Grassland renovation decreased large macroaggregates, microbial and fungal biomass.
- Marked temporal dynamics of aggregates and fungal biomass were observed in permanent grassland.
- Multiple linear regression analysis described the variations in the large macroaggregate concentration satisfactorily.

In grassland soils, the temporal dynamics in different fractions of soil organic carbon (SOC) is not completely understood. We investigated the temporal variations of water-stable aggregates, microbial biomass C (Cmic) and ergosterol concentrations (as a proxy for fungal biomass) in loamy sandy soils under grassland (north of Kiel, Germany). Samples were taken six times between October 2010 and October 2011 from i) a permanent grassland, ii) an arable plot converted to grassland and iii) a grassland with a one-time tillage operation (both in September 2010). Water-stable aggregate concentrations were determined by a wet-sieving procedure, Cmic concentrations by chloroform-fumigation-extraction and ergosterol concentrations by ethanol extraction. Temporal variation in aggregate distribution of soil samples from the permanent grassland was considerable: the large macroaggregate (> 2000 μm) concentrations (mean ± standard error, n = 3) in the surface soil (0-10 cm) were highest in October 2011 (666 ± 12 g kg− 1) and lowest in May (206 ± 49 g kg− 1). The tillage operation in grassland led to lower concentrations of large macroaggregates, ergosterol and Cmic in the surface soil than in the permanent grassland. The conversion of arable land into grassland did not affect macroaggregate concentrations, despite an increase in Cmic (1.4-fold) and ergosterol concentration (3.3-fold) in the surface soil. Multiple linear regression analysis described the variations in the large macroaggregate concentration satisfactorily (R2 = 0.60) and indicated that the gravimetric moisture content and the Cmic concentration had positive effects and the pH a negative effect. While ergosterol concentrations (mean ± standard error) showed some temporal variations (values for the surface soil in the grassland ranged from 0.5 ± 0.1 to 1.5 ± 0.1 mg kg− 1), Cmic concentrations varied much less, indicating a higher sensitivity of ergosterol to soil cultivation or changing environmental conditions.