Victoria A. Marchesini

Salt leaching leads to drier soils in disturbed semiarid woodlands of central Argentina

Disturbances in semiarid environments have revealed a strong connection between water, salt and vegetation dynamics highlighting how the alteration of water fluxes can drive salt redistribution process and long-term environmental degradation. Here, we explore to what extent the reciprocal effect, that of salt redistribution on water fluxes, may play a role in dictating environmental changes following disturbance in dry woodlands. We assessed salt and water dynamics comparing soil-solution electrical conductivity, chloride concentration, soil water content (SWC) and soil matric and osmotic water potential (Ψm, Ψos) between disturbed and undisturbed areas. A large pool of salts and chlorides present in undisturbed areas was absent in disturbed plots, suggesting deep leaching. Unexpectedly, this was associated with slight but consistently lower SWC in disturbed versus undisturbed situations during two growing seasons. The apparent paradox of increased leaching but diminishing SWC after disturbance can be explained by the effect of native salt lowering Ψos enough to prevent full soil drying. Under disturbed conditions, the onset of deep drainage and salt leaching would raise Ψos allowing a decline of Ψm and SWC. Soil water storage seems to be modulated by the presence (under natural conditions) and partial leaching (following selective shrub disturbance) of large salt pools. This counterintuitive effect of disturbances may be important in semiarid regions where deep soil salt accumulation is a common feature. Our results highlight the importance of water–salt–vegetation coupling for the understanding and management of these systems.

Drought tolerances of three stem-succulent halophyte species of an inland semiarid salt lake system

Succulent halophytes of the genus Tecticornia are dominant in salt marshes of inland lakes of Australia. We assessed the drought responses of a C4 species, Tecticornia indica subsp. bidens (Nees) K.A.Sheph. & Paul G.Wilson, and two C3 species, Tecticornia auriculata Paul G.Wilson (K.A.Sheph. & Paul G.Wilson) and Tecticornia medusa (K.A.Sheph. & S.J.van Leeuwen) that occur in the Fortescue Marsh, north-west Australia. In a glasshouse experiment, the three species were grown individually and in different combinations, with varying number of plants per pot to achieve comparable dry-down rates among pots. Prior to the imposition of drought (by withholding water) the three species showed differences in dry mass and physiological variables. As the soil dried out, the three species showed similar reductions of transpiration, osmotic potential and photochemical efficiency. Shoot growth was depressed more than root growth. Tissue water loss from portions of the succulent shoots accounted for ~30% of transpiration during severe drought stress. There was no osmotic adjustment. Shoot tissue concentrations of Na+ and Cl- tended to increase during drought, and those of K+ decreased; however, these changes were not always statistically significant. Chlorophyll concentration decreased but betacyanin concentration increased. Despite occupying distinct positions in a water and salinity gradient, the three Tecticornia species had remarkably similar responses to soil water deficit.

Ecohydrological transformation in the Dry Chaco and the risk of dryland salinity: Following Australia's footsteps?

During the last century the massive conversion of Australian dry forests to crops and pastures triggered the massive soil and groundwater degradation process known as dryland salinity. Currently, South American Chacos dry forests are undergoing a similar transformation, leading global deforestation rates. The goal of this study was to review existing ecohydrological information about natural and cultivated systems in the Chaco to assess the dryland salinity risks. We review deep soil water, salt stocks and groundwater recharge from agriculture/native dry forests stands located in a precipitation range of 450-1100 mm. We complement this with water table level records and geoelectric profiles together with personal observations. We use data from 15 Australian studies for comparison. Strong salt leaching, especially after 20 years of forest clearance, indicates the onset of deep drainage following forest conversion to agriculture in the Dry Chaco. Water stocks were more than double in the cleared stands compared to their dry forest pairs and recharge rates were up to two order magnitude higher in agricultural areas. While in the Dry Chaco lower atmospheric salt deposition, younger sediments, and relatively high water-consuming agricultural systems, attenuate salinization risks compared to Australia, the very flat topography and related shallow water table levels of the South American region could make groundwater recharge and salt mobilization processes more widespread and difficult to manage. The lack of awareness among the general public, farmers and decision makers about this issue amplifies the problem, making land management plans for the Argentine dry forest territories essential.