Tackling water scarcity through treated wastewater in Patagonian steppe: Carbon assimilation, water use and fruit traits in olive trees

One of the most important environmental factors affecting plant development and productivity is water availability. Recently, olive crops have been cultivated in the coastal area of the Patagonian steppe where drier and cold conditions could limit olive production. However, all over the world, irrigation practices using alternative water sources like urban treated wastewater (WW) are constantly increasing. In arid regions, the use of WW for crop irrigation, supplies nutrient rich water while reducing the need for artificial fertilizers. This promotes a circular economy through resource recovery and offers a reliable alternative water supply. Consequently, this study aimed to investigate the impact of using wastewater on the physiological performance and fruit characteristics in olives trees in southeast Patagonia. An experiment with two irrigation treatments (FW: freshwater, WW: wastewater) was conducted in well irrigated young olive trees growing outdoors in individual pots (cvs. Arbosana, Arbequina, Barnea and Hojiblanca). At a physiological level, WW irrigated plants exhibited significantly higher transpiration rates and net carbon exchange, supported by a marked increase in leaf chlorophyll content, which indicates efficient nitrogen uptake from wastewater. In terms of growth and fruit traits, WW promoted the height growth and biomass in several cultivars and led to a significant increase in fruit number per plant, especially in Arbequina and Hojiblanca. Overall, our findings indicate that despite increasing transpiration, the high nutrient load of WW enhances carbon assimilation, suggesting that olive orchards could function as an effective carbon sink. This study showed for the first time , that urban treated wastewater represents a suitable and viable alternative for irrigation in the Patagonian steppe where water scarcity and nutrient poor soils are the major limiting factors for agricultural development. Nevertheless, field studies are essential to fully address the long-term impacts of wastewater irrigation on olive cultivars.