Soil nutrients and microbial biomass in three contrasting Mediterranean forests
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The extent to which the spatial and temporal patterns of soil microbial and available nutrient pools hold across different Mediterranean forest types is unclear impeding the generalization needed to consolidate our understanding on Mediterranean ecosystems functioning.
We explored the response of soil microbial, total, organic and inorganic extractable nutrient pools (C, N and P) to common sources of variability, namely habitat (tree cover), soil depth and season (summer drought), in three contrasting Mediterranean forest types: a Quercus ilex open woodland, a mixed Q. suber and Q. canariensis woodland and a Pinus sylvestris forest.
Soil microbial and available nutrient pools were larger beneath tree cover than in open areas in both oak woodlands whereas the opposite trend was found in the pine forest. The greatest differences in soil properties between habitat types were found in the open woodland. Season (drought effect) was the main driver of variability in the pine forest and was related to a loss of microbial nutrients (up to 75 % loss of Nmic and Pmic) and an increase in microbial ratios (Cmic/Nmic, Cmic/Pmic) from Spring to Summer in all sites. Nutrient pools consistently decreased with soil depth, with microbial C, N and P in the top soil being up to 208 %, 215 % and 274 % larger than in the deeper soil respectively.
Similar patterns of variation emerged in relation to season and soil depth across the three forest types whereas the direction and magnitude of the habitat (tree cover) effect was site-dependent, possibly related to the differences in tree species composition and forest structure, and thus in the quality and distribution of the litter input.
KeywordsSoil fertility Plant-soil interactions Soil carbon Nitrogen Phosphorus
We thank the Consejería de Medio Ambiente (Andalusian Government) and the Direction of the Los Alcornocales Natural Park, Sierra de Cardeña and Montoro Natural Park and Sierra Nevada National Park for the facilities and support to carry out our field work. We are grateful to Susana Hitos, Eduardo Gutiérrez, Carlos Ros, Raquel Casado, Nacho Villegas, Ramón Ruiz and Eulogio Corral for field and lab assistance. This study was supported by the coordinated Spanish MEC Projects DINAMED (CGL2005-05830-C03), INTERBOS (CGL2008- 4503-C03-01), and DIVERBOS (CGL2011-30285-C02), the Andalusian Projects GESBOME (P06-RNM-1890) and ANASINQUE (PE2010-RNM5782), the Life + Biodehesa project (11/BIO/ES/000726), three FPI-MEC predoctoral fellowships to CA, LM and VGR, the Subprograma de Técnicos de Apoyo MICINN (PTA2009-1782-I), a MECD postdoctoral grant E-28-2012-0934030 to CA and a EU Marie Curie fellowship (FP7-2011-IEF-300825) to LM.
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