Evaluation of the trade-off between water use efficiency and nutrient use efficiency in two semiarid coniferous tree species growing on an organic amended metalliferous mine tailing substrate

We evaluated the ecophysiological responses of two semiarid coniferous tree species, Pinus halepensis and Tetraclinis articulata, growing on a nutrient-poor metalliferous mine tailings substrate to organic amendments (biochar and/or organic municipal waste). The trees were grown in mesocosms under irrigated conditions for 20 months. Then, a comprehensive characterization of soil and plant parameters (including stable isotopes) was carried out. Treatments containing municipal waste showed better soil fertility indicators (approximately 2-fold higher organic carbon and total nitrogen concentrations) and higher plant biomass (up to 5-fold higher) than unamended and only biochar treatments. Trees in most of the treatments exhibited leaf N/P ratios <14 indicating severe N limitation of plant growth. Metal uptake was below phytotoxic levels across all the treatments. Leaf δ