WUSSIAAME - Uso da água, estratégias de sobrevivência hídrica e impacto de agroquímicos nos recursos hídricos em ecossistemas

Portugal is one of the European countries with higher contrasts between water availability in wet/cold and dry/warm seasons. Deep rooting, necessary for plant survival during summer, occurs because of the high amounts of water stored in deep soil layers during winter. Hydraulic redistribution – in this context, mostly hydraulic lift – helps plants to become relatively independent from rainy events [25]. As a result, the plants keep their superficial root system alive and the uptake of nutrients from upper dry soil layers continues. Hydraulic lift in late summer, from deep to superficial roots, has been identified in Centre and South Portugal for Quercus suber, by this team [21] and others [17]. Other mechanisms may contribute to plant survival in water scarcity conditions [25] [10], such as those reducing transpiration. Combined strategies, including the ability to increase root water uptake (offer), to reduce water losses (demand) (or to handle dehydration), require an integrated analysis. The Mediterranean ecosystems with natural vegetation, evergreen oak and agricultural woody stands traditionally non irrigated, important for the ecological and economic sustainability, deserve attention due to their ability to withstand extreme climatic conditions, but also because they can be vulnerable to decreasing groundwater availability. Survival of such stands may depend on water uptake from deep soil layers and groundwater. Poor irrigation practices or excessive use in relation to sustainability thresholds endanger groundwater quality and quantity. In Southern Europe, traditional orchards have been replaced by highly productive irrigated ones, increasing water use. Simultaneously there is an increase in agrochemicals use, fertilisers and pesticides, rising water quality problems. However, climate change scenarios give warnings in relation to future water availability. Critical questions arise: which species/stands/cultural systems depend on groundwater and to which extent? How can future land use management policies be supported? How overuse of water endangers the existent stands? In what extent, irrigation practices are neglecting the natural survival mechanisms for water, while increasing the risk of groundwater contamination with agrochemicals? The understanding of these problems and processes contributes to our ability to prevent desertification in vulnerable areas. The aim of the proposed research is to study: 1) which survival mechanisms are present and how important they are, 2) how the relative importance of those mechanisms changes as a result of the new irrigation practices, 3) which is the impact of such new practices in the groundwater availability and quality. The team proposes to work for two years, at plant-stand scale, in two agricultural systems, olive groves (Olea europea,SE Portugal) and vineyards (Vitis vinifera, NE Portugal), irrigated and rainfed. Criteria for choosing these species were: 1) they are economically relevant, 2) traditionally not irrigated and 3) the new stands in the drier regions are commonly irrigated. The reasons for this approach (irrigated/rainfed) were two. Firstly, the comparative analysis of long term (years) nonirrigated and irrigated stands, allows a more sound study of crop water use strategies (Task 1) and the consequences, in a changing climate, of land use modifications towards irrigation (Task 5). Secondly, the experimental set-up and data collection (Task 2), for the integrated analysis of the above, provides a data set for studying aspects such as: a) improving water management with models appropriate for sustainable deficit irrigation, with plant water status as an input, for instance (plant sensing) (Task 3.1) or adjusting empirical models (Task 3.2); b) studying the transport of water and agrochemicals and the impacts on groundwater quality in terms of agrochemicals contamination (Task 4, 5). Survival mechanisms – the main aspect – will be observed in the root (reversible sap flow sensors) and shoot systems. Fluxes to the soil and to the atmosphere will be measured. To our knowledge, such integrated and comparative analysis has not yet been done, for the crops and conditions selected. This interdisciplinary team has know-how for the proposed tasks, with a wide experience on soil water measurements (ISA, UTAD), water stress and drought related ecophysiological aspects, at the shoot level (ISA, FC-UL and UTAD) and on flux measurements in woody crops, at the stand scale (ISA). ISA team actively collaborated in experiments on reverse flow in roots (Tasks 1 and 2). A PhD thesis (supervision of the PI) proposes one of the model approaches we intend to apply (Task 3). The researchers working on water quality (Tasks 4 and 5, at plot and region scale, respectively) have a large experience in field work, laboratory analysis and modelling water and agrochemicals in the soil profile and environmental risk assessment. In all specific items where complementary expertise is advisable, consultants were invited to collaborate.