Rapid development and application of nanomaterials and nanotechnology make assessment of their potential health and environmental impacts on humans, non-human biota, and ecosystems imperative. Here we show that pumpkin plants (Cucurbita maxima), grown in an aqueous medium containing magnetite (Fe₃O₄) nanoparticles, can absorb, translocate, and accumulate the particles in the plant tissues. These results suggest that plants, as an important component of the environmental and ecological systems, need to be included when evaluating the overall fate, transport and exposure pathways of nanoparticles in the environment.

Enhancement of plant drought stress tolerance by plant growth‐promoting rhizobacteria (PGPR) has been increasingly documented in the literature. However, most studies to date have focused on PGPR‐root/plant interactions; very little is known about PGPR's role in mediating physiochemical and hydrological changes in the rhizospheric soil that may impact plant drought stress tolerance. Our study aimed to advance mechanistic understanding of PGPR‐mediated biophysical changes in the rhizospheric soil that may contribute to plant drought stress tolerance in addition to plant responses. We measured soil water retention characteristics, hydraulic conductivity, and water evaporation in soils with various textures (i.e., pure sand, sandy soil, and clay) as influenced by a representative PGPR (Bacillus subtilis strain UD1022) using the HYPROP system. We found that all PGPR‐treated soils held more water and had reduced hydraulic conductivity and accumulative evaporation, compared to their corresponding controls. We discuss three mechanisms, due to B. subtilis incubation or production of extracellular polymeric substances (EPS), that are potentially responsible for the changes in hydraulic properties and soil evaporation: (i) EPS have a large water holding capacity; (ii) EPS alter soil matrix structure and connectivity of pore space; (iii) EPS modify the physicochemical properties of water (surface tension and viscosity). These results clearly demonstrate PGPR's ability to increase water availability to plants by slowing down evaporation and by increasing the time available for plants to make metabolic adjustments to drought stress.