Effects of woodland maturity, vegetation cover and season on enzymatic and microbial activity in thermophilic Spanish Juniper woodlands (Juniperus thurifera L.) of southern Spain

摘要

There are still considerable uncertainties about soil functioning in semi-arid Mediterranean ecosystems. Hence, studies that have focused on Juniperus species in thermophilic Mediterranean woodlands are practically non-existent. This study provides a survey of the effects of (i) woodland maturity (mature and young woodlands), (ii) vegetation cover (Juniperus thurifera L. trees, Rosmarinus officinalis L. shrubs and semi-wooded grasslands) and (iii) growing season (spring, summer and autumn) on soil enzymatic activity (urease, alkaline phosphatase and beta -glucosidase) and microbiological characteristics (microbial biomass C (MBC), basal respiration (Br), and microbial and metabolic quotients) in thermophilic Spanish Juniper woodlands. The results showed that mature woodland maintained a greater enzymatic and microbiological activity than the more productive young woodland. The advanced communities of Juniperus trees and Rosmarinus shrubs exhibited greater enzymatic and microbial activity than grassland areas. Soil biological characteristics were strongly affected by the season. Significant beta -glucosidase activity and Br were observed in the summer, as a consequence of the greater organic matter availability for microbes, despite the reduced soil moisture availability. Thus, foliar abscission in trees and shrubs and withering in grasslands seem to control soil biological activity. Hence, we hypothesize that microbial communities that are adapted to drought exist. In contrast, the presence of greater N and P content in summer seems to reduce the urease and phosphatase activities. In addition, the more advanced communities (Juniperus and Rosmarinus covers, especially in mature woodland) showed an inherent trend towards efficiency in C utilization throughout the growing seasons, thus increasing the MBC at the end of the growing season.