Mon, Aug 02, 2021:On Demand
Background/Question/Methods
European beachgrass (Ammophila arenaria) is one of the most problematic invaders of coastal dune ecosystems, often forming dense, monotypic stands that suppress growth of native species. At Point Reyes National Seashore (PRNS), many efforts have been made to control Ammophila, including herbicide treatment. However, the invader continues impeding restoration of native dune communities after treatment, as dead beachgrass can persist on the landscape for years. Phytochemical analysis of Ammophila collected at PRNS revealed that while the samples had higher C:N ratios than native grasses, differences in plant chemistry did not account for the large delays in decomposition. Previous studies showed that soil microbial communities at PRNS differ between invaded, native, and herbicide treated habitats. We hypothesized that these changes in soil microbe communities contribute to the delay in decomposition of Ammophila arenaria. We conducted a litterbag experiment in the dunes of PRNS. We filled Nylon mesh bags with either naturally senesced Ammophila or Ammophila that had been treated with 1.5% imazapyr, 2% glyphosate, a modified vegetable oil surfactant, and blue dye. We constructed bags with differing mesh sizes (1mm or 60 micron) to begin untangling the relative contributions of microbes and soil invertebrates to the decomposition of Ammophila. Blocks containing pairwise treatments were placed in three habitat types: native Dune Scrub habitat, highly invaded habitat, and sites where Ammophila had been chemically treated. We measured change in biomass after 2.5 months.
Results/Conclusions We predicted different habitats would show different rates of Ammophila arenaria decomposition. Instead, we found that habitat had no significant effect on change in biomass during this time period, although herbicide treated material showed marginally higher rates of biomass loss in herbicide treated plots. We predicted that naturally senesced material would have a higher percentage of biomass loss compared to herbicide treated material. Interestingly, we found that herbicide treated material had higher rates of biomass loss. These preliminary results suggest that differences in soil microbial communities might not account for the delay in decomposition of herbicide treated Ammophila arenaria. However, a few months in the field might not be enough to detect differences in microbial activity. We will sample these plots again at 8 and 12 months from initial deployment, which will allow us to see if these slight differences in decomposition rate change over time. Understanding the factors affecting decomposition of this highly invasive species is vital for restoring invaded habitats at Point Reyes National Seashore and beyond.
Results/Conclusions We predicted different habitats would show different rates of Ammophila arenaria decomposition. Instead, we found that habitat had no significant effect on change in biomass during this time period, although herbicide treated material showed marginally higher rates of biomass loss in herbicide treated plots. We predicted that naturally senesced material would have a higher percentage of biomass loss compared to herbicide treated material. Interestingly, we found that herbicide treated material had higher rates of biomass loss. These preliminary results suggest that differences in soil microbial communities might not account for the delay in decomposition of herbicide treated Ammophila arenaria. However, a few months in the field might not be enough to detect differences in microbial activity. We will sample these plots again at 8 and 12 months from initial deployment, which will allow us to see if these slight differences in decomposition rate change over time. Understanding the factors affecting decomposition of this highly invasive species is vital for restoring invaded habitats at Point Reyes National Seashore and beyond.