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Abstract Sand‐clay mixtures are common in both freshwater and saltwater environments, yet how they behave under different levels of salinity remains poorly understood. Here, we demonstrate the impact of salinity on the rheological properties and erosion threshold of sand‐clay mixtures through systematically controlled flume experiments and rheological measurements. Mixtures with a representative bentonite‐to‐sand ratio typical of natural estuarine and coastal sediments were prepared at salinities ranging from 0 to 35 parts per thousand (ppt), spanning freshwater to seawater conditions. We measured viscosity, flow‐point stress, and yield stress of the mixtures using a rheometer and determined the critical bed shear stress in a water‐recirculating flume. Our results indicate that as salinity increases from 0 to 35 ppt, the critical bed shear stress decreases by about two orders of magnitude, from about 60 Pa at 0 ppt to less than 1 Pa at 35 ppt. Similarly, both the flow‐point stress and yield stress decreased by over two orders of magnitude with increasing salinity. These changes correspond to a salinity‐induced transition of the sand‐bentonite mixture from a cohesive, strong‐gel state in freshwater (0 ppt), to a weak‐gel state between 3 and 10 ppt, and finally to a fluid‐like state above 10 ppt. Our research highlights the important role of salt in controlling the rheological properties and erosion threshold of fresh, non‐consolidated deposits of sand‐clay mixtures, with implications for predicting coastal landscape evolution and designing erosion‐control strategies.
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Salinity legacy: Foliar microbiome's history affects mutualist‐conferred salinity tolerance
Abstract The rapid human‐driven changes in the environment during the Anthropocene have placed extreme stress on many plants and animals. Beneficial interactions with microorganisms may be crucial for ameliorating these stressors and facilitating the ecosystem services host organisms provide. Foliar endophytes, microorganisms that reside within leaves, are found in essentially all plants and can provide important benefits (e.g., enhanced drought tolerance or resistance to herbivory). However, it remains unclear how important the legacy effects of the abiotic stressors that select on these microbiomes are for affecting the degree of stress amelioration provided to their hosts. To elucidate foliar endophytes' role in host‐plant salt tolerance, especially if salinity experienced in the field selects for endophytes that are better suited to improve the salt tolerance of their hosts, we combined field collections of 90 endophyte communities from 30 sites across the coastal Everglades with a manipulative growth experiment assessing endophyte inoculation effects on host‐plant performance. Specifically, we grew >350 red mangrove (Rhizophora mangle) seedlings in a factorial design that manipulated the salinity environment the seedlings experienced (freshwater vs. saltwater), the introduction of field‐collected endophytes (live vs. sterilized inoculum), and the legacy of salinity stress experienced by these introduced endophytes, ranging from no salt stress (0 parts per thousand [ppt] salinity) to high salt stress (40 ppt) environments. We found that inoculation with field‐collected endophytes significantly increased mangrove performance across almost all metrics examined (15%–20% increase on average), and these beneficial effects typically occurred when the endophytes were grown in saltwater. Importantly, our study revealed the novel result that endophyte‐conferred salinity tolerance depended on microbiome salinity legacy in a key coastal foundation species. Salt‐stressed mangroves inoculated with endophyte microbiomes from high‐salinity environments performed, on average, as well as plants grown in low‐stress freshwater, while endophytes from freshwater environments did not relieve host salinity stress. Given the increasing salinity stress imposed by sea level rise and the importance of foundation species like mangroves for ecosystem services, our results indicate that consideration of endophytic associations and their salinity legacy may be critical for the successful restoration and management of coastal habitats.
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- PAR ID:
- 10445036
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Ecology
- Volume:
- 103
- Issue:
- 6
- ISSN:
- 0012-9658
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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