Root-surface phosphatase activities were measured in natural and semi-natural shrublands across an European climatic gradient of temperature and rainfall including Wales (WL), Denmark (DK), Netherlands (NL), Hungary (HU), Italy (IT) and Spain (SP). In each site a warming experiment was conducted since 1999 or 2001 by means of passive night-time warming using reflective curtains that covered the vegetation at night. The treatments increased yearly average soil temperatures around 0.8 o C in most of sites. Root-surface phosphatase activity values ranged between 56 mg PNP g -1 h -1 in IT and 3.5 mg PNP g -1 h -1 in HU. Warming had no effect on root-surface phosphatase acti vity across the sites and only in Hungary a slight increase was detected. Plants at Mediterranean sites (IT, SP) showed a higher root-surface phosphatase activity than plants at temperate sites (WL, NL, DK). We suggest it might be an adaptation of plant species evolved under Mediterranean climate that allows them a) to compensate in wet period for the decrease in phosphatase activity, and thus P uptake, during drought periods, and/or b) to benefit from soluble organic P flushes following the frequent drying-rewetting episodes experienced by soils in Mediterranean ecosystems

This research was funded by EU under the VULCAN project (Contract EVK2-CT-2000-00094). We also thank partial funding by Spanish Government grants REN2003-04871/GLO and CGL2004- 01402/BOS, Catalan government grant SGR2005-00312, the EC Integrated FP6 ALARM (GOCE-CT-2003-506675) Project, and a Fundación BBVA 2004 grant. Marc Estiarte acknowledges support from “Ministerio de Educación y Ciencia” (Ramón y Cajal contract)

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Peer reviewed