Biochar amendment as a strategy to reduce hydric stress in Eucalyptus

keywords Atmospheric CO2 concentrations are higher than any time in the last decades, resulting in global warming along with general climactic changes. Drought stress is one of the most important effect of climactic alterations and directly disrupts water and carbon fluxes, with effects on primary production and terrestrial ecosystems equilibrium. It affects plants at different levels depending on intensity, duration and progression of drought, leading to responses at physiological, biochemical and molecular levels. The biochar application to the soils as a mitigation agent, by enhancing water and nutrient availability, has been well documented. Assuming the economic importance of Eucalyptus globulus in Portugal and the rising demand of dry periods in mediterranic region, the main goal of this study was to evaluate the ability of biochar to reduce the stress effects in Eucalyptus globulus plants, under water limiting conditions. We also evaluate the application of fertilizers in plant performance and the conjugation of both. For this propose, 136 plants of Eucalyptus globulus were subjected to a 6 weeks period assay, divided by 2 groups (well watered – 80% of field capacity and water stress 30% of field capacity), which one with 4 treatments: without biochar, with biochar (6%), without biochar+fertilizer and with biochar+fertilizer. At the end of the experimental period, the plants were evaluated at morphological, physiological and biochemical levels. Our results showed a significant decrease in most of analysed parameters with water limitation, as gas exchanges, hydric potential, height, transpiration, lateral branches, leaf area and number of leaves, photosynthesis (except WSb), above ground biomass (fresh and dry) and weight of roots, suggesting that the water limitations severely affect plants performance. Biochar application improve leaf area and photosynthesis rates along with decreases the total soluble sugars content and slight higher values of water potential, suggesting that in water stress conditions it is beneficial to applied biochar into soils to enhance their ability to store and use water, reducing overall stress levels in the plants. In well watered conditions, the biochar showed wilting signals In well watered conditions the use of biochar promoted lower photosynthetic rates and lower values of all morphological parameters as above ground biomass, number of lateral branches and leaf area when compared with nutrients application, along with apical wilting signals suggesting that in in well water conditions, the use of biochar is not a better option. The results of conjugation of both biochar and fertilizers were contradictory. In well water conditions we found a higher values of Fv/Fm along with chlorophylls and lower values of number of leaves, leaf area, photosynthesis and TSS. Otherwise, in water stress conditions and besides the lower performance in all gas exchanges parameters, we noticed higher above ground biomass, when compared with biochar and fertilizer applied alone. In conclusion, our results shows that biochar amend water limitation conditions in E.globulus, but is not a main value for plant performance in well water conditions or when applied together with fertilizer. In either case, further studies are needed.