Seasonal Variation of Soil Microbial Biomass Carbon and Nitrogen as Affected by Land Use in a Mediterranean Agro Ecosystem.

Abstract

ABSTRACT Soil microbial biomass carbon (Cmic) and nitrogen (Nmic) dynamics were studied in five representative land use of Mediterranean agroecosystems over two consecutive years on a seasonal basis on the island of Lesvos, Greece. Soil samples from natural forests, olive groves, wheat cultivations, pasture, and annual crop rotation were collected from plots that had been managed conventionally according to local practices. The Cmic and Nmic values ranged from 86.8 to 565.1 and from 14.7 to 101.6 mg kg-1 dry soil, respectively, being affected by both land use and season. Their average values increased in the order of arable < forest ≤ pasture. Similar to all land uses, Cmic and Nmic showed a significant, land-use dependence with seasonal variation. Specifically, summer minima and autumn maxima highlighted how hot and dry Mediterranean summers affect the activity of soil micro-organisms. Cmic to organic C (Corg) and Nmic to total N (Ntot) ratios ranged from 1.3 to 4.0 and 2.0 to 11.2, respectively, and were also affected by land use and season. Seasonal variation of Cmic to Corg and Nmic to Ntot ratios followed the general trend of Cmic and Nmic only in the land uses that do not incorporate crop residues. The Cmic: Nmic average ratio was 6.86 and was the only one soil microbial biomass parameter studied where seasonal variability exceeded land-use variability.