Global climate change includes shifts in temperature and precipitation, increases in the frequency and intensity of extreme weather events, and sea level rise, all of which will drastically impact coastal ecosystems. Because plant population persistence depends on successful seedling recruitment, seedling survival to maturity, and reproduction, it is important to consider how increased salinity due to sea level rise and increasing storm surges will influence each of these key life history processes. The aim of this study is to quantify salinity tolerance across wholeplant ontogeny and to identify physiological mechanisms underlying tolerance across ontogeny in a widespread and abundant native coastal plant species, Jacquemontia sandwicensis (Convolvulaceae). At the seed, seedling, juvenile, and mature ontogenetic stages, plants were exposed to three weeks of salinity watering treatments. Tolerance was assayed as the performance of stressed compared to control plants using multiple fitness metrics, including germination, survival, growth, and reproduction. Potential physiological mechanisms underlying salinity tolerance were measured at each ontogenetic stage, including: photosynthesis and stomatal conductance rates, leaf area, thickness, leaf mass per area, biomass allocation, leaf mineral content, and sequestration of salt ions in roots and leaves.
Results/Conclusions
At high salinity levels germination is significantly reduced, yet a high proportion of seeds remained viable when transferred to distilled water treatment. In seedling and juvenile stages, photosynthesis rates are maintained despite reduced conductance. High salinity levels led to significant increases in leaf mass per area and water use efficiency, responses that mimic drought-induced plasticity. Under high salinity, the root:shoot ratio of seedlings increased significantly, indicating high responsiveness to osmotic stress. While no stage is fully tolerant of increasing salinity levels, variations in resource allocation in response to salinity exposure differs significantly across plant developmental stages. Trait plasticity enables the avoidance of salinity stress at early life stages, however, delayed onset of flowering and reduced seed set indicate that salinity exposure at different life stages may threaten species resilience under future climate change.