Sap Flow Measurements for the Evaluation of Poplar Clone Performance in Remediation of Soil Polluted with Olive Mill Wastewater

The olive oil mill wastewater (OMWW) or ``vegetation water\{''\} derives from the extraction of olive (Olea europaea L.) oil and contains suspended matter consisting of pulp, mucilage, pectin, oil, etc., in a relatively stable emulsion. The use of these wastewaters on soils may enhance their fertility. However, the long term use of OMWW as fertilizer may lead to some disadvantages because of its potential leaching into the water table. In order to prevent this environmental problem in Italy a maximum application rate of 80 m(3) ha(-1) year(-1) is allowed. The use of plants characterized by high water consumption, such as poplar, could be a means to limit water table pollution problems, while enhancing the OMWW degradation, through the intensive interactions activated in the system root-soil-water-microrganisms. Selection of poplar clones with high transpiration rate is compulsory for OMWW remediation purposes, though should be balanced with water saving potential, particularly in the Mediterranean environment. With this aim, a pilot system of Short Rotation Coppice (SRC) poplar plantation was established in spring 2009, in soil polluted with OMWW. The poplar clones used were Populus x euramericana clone I-214 and Populus x generosa x Populus nigra clone Monviso, with contrasting functional and structural traits. After one year, sap flow measurements were done using the thermal dissipation method. Data were recorded connecting the probes to an acquisition data system composed by a low cost open-source electronic platform. Sap flow results showed significant differences between clones in transpiration during dry and wet period. This result can be effectively used for the selection of superior-performing hybrid poplar genotypes exhibiting great potential for phytoremediation applications, where high water usage is a key trait for the success of the system. Further analysis on plant biomass of the two clones and soils treated with OMWW are in progress to confirm the correlation between the poplar higher evapotranspiration capacity and the remediation of OMWW.