Location: Exotic and Invasive Weeds Research
Project Number: 2030-22000-024-05
Start Date: Aug 01, 2013
End Date: Aug 01, 2014
1) Hypothesis: Does ploidy level of Ludwigia congeners contribute to invasiveness? Approach: Invasive Ludwigia include diploid, hexaploid and decaploid cytotypes. Understanding of plant traits and tolerances of cytotypes will guide management strategies. Experiments will be conducted in aquatic mesocosms. First, we will test the hypothesis that polyploids have higher nutrient acquisition and growth rates than diploids during establishment. L. peploides (diploid) and L. hexapetala (decaploid) will be randomly assigned to pots with two levels of sediment nutrients at levels measured at invaded sites in the Russian River watershed, and submersed at 45cm depth among four outdoor mesocosms. Initial measures will include shoot weight and length, and rooting node, leave and branch counts. We will record photosynthetic parameters. At harvest, plants will be separated by anatomy for biomass allocation, and to calculate relative growth rates, leaf area, LMR, RMR, tissue C and N, and photosynthetic nitrogen use efficiency. In Phase 2, we will compare L. grandiflora, L. hexapetala and L. peploides responses to resource gradients in greenhouses. Contingency: Can use controlled environment chambers and sequential experiments. 2) Hypothesis: Do environmental variables explain spatial expansion of L. hexapetala in the Russian River? Approach: Mechanisms that drive expansion of L. hexapetala are currently poorly understood, and their definition may assist in prediction of future spread and development of control methods. Field study reaches will be spatially stratified along the Russian River. Using GPS-GIS technology we will document patch size, distribution and abundance of invasive L. hexapetala. We will measure a suite of environmental variables (e.g. plant community composition, light, soil and water nutrients, water velocity, channel complexity) in extant and expanding patches, statistically analyze relationships in these data, evaluate where patches are expanding, and rates of spread by comparison with 2012 baseline data. Contingency: Number of sites and variables can be adjusted. Sonoma County Water Agency will provide access. 3) Hypothesis: Does growth and nutrient allocation of invasive L. hexapetala vary across water quality and depth gradients? Approach: Understanding spatial and temporal variation of weaknesses in the weed’s life cycle will contribute to management strategies. Plant tissue, soil and water quality samples will be evaluated from 3 sites in the Russian River watershed. Five random, replicate transects per invaded river site will be sampled along water depth gradients. Seasonal sampling will correspond to major life stages of the plants: pre-reproductive growth, flowering, seed dispersal, and semi-dormant. Samples will be separated by location relative to the water column (above, below) and by anatomy to determine total biomass and allocation. Plant tissue will be analyzed for C, N, and P for nutrient allocation. Storage organs will be analyzed for nonstructural carbohydrates to evaluate resprouting capacity. Data will be analyzed with MANOVA or Kruskal-Wallis ANOVA. Contingency: Can use controlled environment chambers.