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Abstract Anthropogenic salinization resulting from road salt application can degrade aquatic environments by altering the structure and function of phytoplankton communities, ultimately reducing flows of resources through aquatic food webs. However, physiological mechanisms underlying taxon‐specific responses to salinization are often poorly linked to higher‐order ecosystem dynamics, limiting our ability to predict community responses to salinization. To this end, we tested hypotheses derived from Subsidy‐Stress and Ecological Stoichiometry theory by growing two cosmopolitan genera,Dolichospermum(prokaryotic, cyanobacteria) andScenedesmus(eukaryotic, green algae), across NaCl gradients and contrasting differences in their growth rates, degree of Na homeostasis, and cellular C : N : P ratios. We found mixed support for the subsidy‐stress hypothesis, with only stress responses observed for both species. Instead, growth declines appeared to be linked to stoichiometric tradeoffs between growth and homeostatic regulation, with stronger homeostatic Na regulation coinciding with a greater reduction inScenedesmusgrowth rates and higher variation in their stoichiometric C : N : P ratios across NaCl gradients. Nonhomeostatic Na regulation allowedDolichospermumto sustain higher growth rates, which appeared to constrain variation in their stoichiometric C : N : P ratios along with their stronger physiological regulation of intracellular P storage molecule production. Differences in phytoplankton growth responses were consistent with stoichiometric theory and field observations documenting shifts from green algae to cyanobacteria in response to freshwater salinization. Our results suggest that these shifts could take place below existing North American chronic threshold limits, resulting in decreased production at higher trophic levels by reducing phytoplankton biomass production rates and inducing nutritional stress in consumers. 

Prairie habitat loss in the United States has led to population declines in many prairie-associated species, including Ornate Box Turtles (Terrapene ornata). Northwest Arkansas is an intergrade zone between the prairie-dwelling T. ornata and the more forestassociated Three-Toed Box Turtle (Terrapene carolina). As such, limited information exists on the potential differences in physiology and thermal ecology between the two box turtle species and how those differences might influence their habitat use. We addressed gaps in our knowledge of the thermal and spatial ecology of T. ornata and T. carolina with a three-part study. First, we compared the thermal profiles of refugia, open, and vegetated microhabitats across degraded prairie, restored prairie, and adjacent forest macrohabitats using operative temperature models and a linear mixed effect model. Second, we measured total evaporative water loss of both species across a range of body sizes. Finally, we fitted a subset of turtles with iButton data loggers and monitored them in the field to examine carapace temperatures and habitat use. Operative temperature models recorded high, largely homogeneous temperatures across microhabitats in degraded prairie and heterogeneous temperatures across restored prairie microhabitats, while forest habitat maintained stable, cool temperatures. Both species exhibited similar evaporative water loss rates; however, T. ornata experienced a broader range of temperatures in the field. Terrapene ornata were exclusively found in prairie habitat, whereas T. carolina was often found in forested habitats and subsurface refugia. Our results demonstrate key differences in box turtle thermal biology and highlight suboptimal thermal characteristics in degraded prairie and forest habitat that should be considered in prairie restoration and management for T. ornata conservation.