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United States Department of Agriculture

Agricultural Research Service

Research Project: Continuing Study of Factors Influencing Spread, Establishment, and Management of Invasive Ludwigia Species

Location: Exotic and Invasive Weeds Research

Project Number: 5325-22000-024-07
Project Type: Interagency Reimbursable Agreement

Start Date: Apr 30, 2014
End Date: Sep 30, 2015

Objective:
Recent aggressive spread of Ludwigia species (Onagraceae) has impacted aquatic and riverine ecosystems in Pacific west states and Florida. Ludwigia taxa are considered among the most aggressive plant invaders in the world. These aquatic weeds rapidly form dense floating mats that degrade water quality, increase flood risk, alter fish and wildlife habitat, and displace native vegetation. Rapid expansion of Ludwigia on the Russian River, and continued expansion in the Sacramento Delta as well as numerous other sites in California, Oregon, and Washington has resource managers concerned. A similar rapid expansion of two Ludwigia polyploids has been observed in Florida on the St. John's River and Kissimmee Chain of Lakes. Continued expansion of invasive Ludwigia into key resources such as the Sacramento Delta and key restoration projects such as the Kissimmee River restoration and acquired lands under the Comprehensive Everglades Restoration Program looks to be inevitable. Current management efforts are limited and there is no consensus on best management practices. There are few published studies regarding invasion biology and management of Ludwigia. As pressure increases to manage a variety of Ludwiga polyploids, there is a need to develop baseline biology data to optimize control efforts in a variety of lotic and lentic sites. The focus areas of this work are to: 1) Evaluate the response of diploid, hexaploid and decaploid species of Ludwigia to environmental conditions. 2) Determine the mechanism(s) and environmental factors driving spatial expansion in patches of L. hexapetala in the Russian River, California. 3) Determine seasonal patterns in allocation of biomass in L. hexapetala along water quality and depth gradients in the Russian River watershed.

Approach:
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.L

Last Modified: 9/21/2014
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