Vegetation is essential to the growth and stability of coastal sand dunes. But establishment is difficult in saline soils typically low in nutrients and moisture. Our project evaluated three potential approaches to ameliorating these stresses: (1) Choosing tolerant plant species, (2) fertilizing and (3) sourcing sand rich in native microbiota that facilitate the uptake of water and nutrients and that reduce salt stress in some species. (Some of these methods may work at cross purposes, with previous studies suggesting that a surplus of nutrients, particularly phosphorus, may disrupt mutualistic mycorrhizal fungal relationships.) We planted two common native dune grasses – Uniola paniculata and Panicum amarum – in sterile soil and soil amended with sand from existing vegetated dunes. We then subjected them to one of two treatments: a salinity gradient (0-2.5%) and a range of nutrient additions (9% phosphorus, 15% nitrogen, nitrogen + phosphorus, and 19-6-12 Osmocote fertilizer). At harvest, we measured live above-ground biomass and extra-radical hyphae in the soil.
Results/Conclusions
The results showed U. paniculata moderately more tolerant of high salinity, while P. amarum responded much more robustly to nutrient additions, producing more than double the growth in biomass from the control. The nutrient additions did not significantly reduce mycorrhizal fungal growth, and in fact, a slow-release balanced fertilizer promoted it. Fertilizing P. amarum therefore may support rapid biomass accumulation without impairing beneficial mutualisms. But because of the weaker response of U. paniculata, fertilization may foster P. amarum’s dominance at the cost of community diversity. And, because of U. paniculata’s greater salt tolerance, maintaining both species in restoration work would likely increase overall community resilience.