Examining effects of elevated temperature, pH, and salinity on early growth of Zizania palustris L. to improve restoration outcomes in Michigan lakes

Abstract

Naturally occurring populations of Zizania palustris have declined in abundance since the 1800s. Due to its cultural, economic, and ecological importance, it has been the target of restoration. We aimed to inform restoration of Z. palustris in Michigan by performing experiments examining how conditions in restoration sites and future human impacts such as warmed water and elevated salinity affect Z. palustris during early phenophases. In a mesocosm study, we raised pH to levels seen in Wycamp Lake (over 8.5), where Z. palustris restoration success was limited, and found decreased germination by 50% and seedling biomass by 60%. No other responses analyzed were influenced by pH whereas increasing water temperature to 24 °C, simulating warming with climate change and warm spring conditions found in Wycamp Lake, decreased germination by 80%, decreased root and shoot biomass by 30 and 40%, respectively, caused spindly shoot morphology, and accelerated onset of germination by 1.2 days and floating leaf phenophase by 3.6 days. With concerns about road salt impacts on restored Z. palustris populations, we raised salinity to 500 mg NaCl L⁻¹ in a mesocosm experiment with no impact. A growth chamber experiment showed that adding NaCl up to ~ 1000 mgL⁻¹ increased Z. palustris biomass and germination with negative impacts above that threshold. In conclusion, Z. palustris is somewhat tolerant of increased salinity. However, high pH and warm water could impact restoration outcomes in Michigan lakes with warm spring water likely becoming a larger concern for Z. palustris restoration with climate change.