Are vegetative reproduction capacities the cause of widespread invasion of Eurasian Salicaceae in Patagonian river landscapes?

Groundwater-surface water interactions in a semi-arid irrigated agricultural valley: A hydrometric and tracer-aided approach

The purpose of this study was to assess hydrological controls (e.g., rainfall, irrigation practices, river discharge, dam operation, evaporation) on surface (SW)- ground water (GW) interactions in an irrigated valley within semi-arid Patagonia Argentina (-65.49 W, -43.29 S). We combined different sampling designs (watershed/sub-watershed scales, longitudinal and monthly samplings) from 2015 to 2019 to investigate the temporal and spatial variation of hydrometrics, electrical conductivity (EC) and stable isotope composition of surface and ground water. Results showed that plant transpiration in the upper basin, evaporation in the middle basin and the reservoir dynamics modified water salinity and left an imprint in stable isotopes. Water tables in the irrigated valley were high (0.5-2 m level from soil surface) and presented higher salinity than river water. Groundwater salinity, temporal variation of water table levels and stable isotopes suggested that groundwater is subjected to evaporation, is recharged from field seepage and, at a lesser extent, from local rainwater. River salinity increased downstream of the irrigated valley during the whole study period (3 years), showing the effects of agriculture and urbanization. EC also responded to the opening and closing of irrigation channels. EC and daily discharge statistical analysis revealed that groundwater recharge the stream below a threshold discharge of 26 m.s-1; with river salinity increasing linearly as daily discharge decrease. This study illustrates the deep modifications that agricultural systems, mainly surface irrigation, produce on semiarid watersheds. Given that SW and GW components are currently not isolated and flow regulation and irrigation practices are playing a critical role in soil quality and river chemistry at low flow conditions, a conjunctive water management strategy must be implemented in order to prevent further land and water quality degradation.

Belowground inter-ramet water transport capacity in Populus euphratica, a Central Asian desert phreatophyte

Populus euphratica Oliv. is a widespread phreatophytic tree species that forms riparian forests in (hyper-)arid regions of Central Asia. Its recruitment strongly relies on vegetative propagation from 'root suckers' that emerge from underground root spacers. The water transport through the spacers, although decisive for emerging ramets, has only rarely been quantified, but is crucial for the vegetative regeneration of the forests. In root spacers with different diameters collected from a mature poplar forest in northwest China, we calculated the hydraulic conductivity (k_c ) from anatomical investigations on the basis of a modified Hagen-Poiseuille equation and measured it (k_m ) with a perfusion solution in the laboratory. The k_m values were compared with the water use by young and mature P. euphratica trees determined in previous studies. We obtained a significant correlation between k_m and k_c (which, however, was higher by at least one order of magnitude). Due to the extensive occurrence of tyloses, particularly in older conduits and thicker spacers, and because the conduit area did not increase with spacer diameter, neither k_c nor k_m increased with an increase in spacer diameter. The water supply through the spacers would be sufficient to meet the water demand even of mature trees. Our results provide a mechanistic explanation for the observed occurrence of P. euphratica clones across large areas and, provided that they are also valid for stands with larger distances to the water table, for the sustained growth and vegetative reproduction of P. euphratica stands growing at larger distances from the groundwater.

Beaver-generated disturbance extends beyond active dam sites to enhance stream morphodynamics and riparian plant recruitment

Given the direct effects of their dams on hydrology, sediment storage, and vegetation, beaver are widely acknowledged as ecosystem engineers. Here we explore the effects of beaver activity on channel processes and riparian plant recruitment beyond those dams and after dam abandonment in southwestern Montana, USA. Willow cuttings from beaver herbivory are commonly deposited along point bars, adding roughness and promoting sediment accumulation. Most cuttings are found <1 km downstream of an active dam. These cuttings often sprout, aiding in willow colonization and bar stabilization. Thirty-four radiocarbon ages show that beaver cuttings have accumulated by similar processes over thousands of years, adding to floodplain carbon storage. Breached dams can initiate meanders, increasing channel and riparian habitat diversity. Beaver activity thus generates a cycle of frequent disturbance, from dam building and riparian plant browsing through dam failure and abandonment, with each phase influencing channel and floodplain evolution and riparian plant recruitment.