Links between vegetation patterns, soil C and N pools and respiration rate under three different land uses in a dry Mediterranean ecosystem
Soil respiration (R s) is controlled by abiotic soil parameters interacting with characteristics of the vegetation and the soil microbial community. Few studies have attempted a comprehensive approach that simultaneously addresses the roles of all the major factors known to influence R s. Our goal was to explore the links between heterogeneity in R s, aboveground plant biomass and belowground properties in three representative land-use types in a dry Mediterranean ecosystem: (1) a 150-year-old mixed Aleppo pine-kermes oak open forest, (2) an abandoned agricultural field, which was cultivated with cereal for several years until abandonment in 1980, when establishment of typical Mediterranean shrubland vegetation started and (3) a rain-fed olive grove, which has been cultivated for 100 years.
Materials and methods
We selected two distinctive sampling periods coinciding with annual minimum or near minimum (December) and maximum (April) rates of R s in this dry Mediterranean ecosystem. In each sampling period, R s, temperature and moisture, aboveground plant biomass, carbon (C) and nitrogen (N) contents in both light and heavy soil organic matter fractions, extractable dissolved organic C (EDOC), as well as microbial and fine root biomass were measured within each land-use type.
Results and discussion
Across sites, R s rates were significantly higher in April (3.07 ± 0.1 μmol m−2 s−1) than in December (1.30 ± 0.1 μmol m−2 s−1). The labile soil organic matter fractions (light fraction C and N contents, microbial biomass C and EDOC) were consistently and strongly related to one another, and to a lesser extent, to the C and N contents in the heavy fraction across sites and seasons. Linear models adequately explained a large proportion of the within-site variability in R s (R 2 values ranged from 41 to 91 % depending on land use and season) but major controls on R s differed considerably between sites and seasons. Primary controls on spatial patterns in R s were linked to recent plant-derived C inputs in both forest and olive grove sites. However, in the abandoned agricultural field site R s appeared to be mainly driven by microbial activity, which could be sustained by intermediate or recalcitrant C and N pools derived from previous land use.
Conversion of native woodland to agricultural land and subsequent land abandonment leads to profound changes in the relationships between R s, aboveground biomass and belowground properties in this dry Mediterranean ecosystem. While above- and belowground vegetation are the primary controls on spatial variability in labile soil C pools and R s in the open forest and olive grove sites, a complete lack of influence of current vegetation patterns on soil C pools and respiration rates in the abandoned agricultural field was observed.
KeywordsAboveground biomass Carbon cycle Land-use change Mediterranean ecosystem Soil organic carbon pools Soil respiration
This research was supported with funds provided by the Spanish CICYT (ERHIBAC project, GGL2004-03179 BTE; PROBASE project, CGL2006-11619 HID), the SENECA Foundation of the Murcia Regional Government, and the Spanish Ministerio de Medio Ambiente (RESEL project). We thank Javier Melgares, the owner of the experimental area, and Sebastian for their great interest in helping us during our work, the members of the Soil and Water Conservation Department at CEBAS-CSIC, who helped us in the lab and field work, and the Carbon Management and Sequestration Center (Ohio State University) for help with organic matter fractionation and chemical analyses.
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