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ARS Home » Pacific West Area » Albany, California » Western Regional Research Center » Invasive Species and Pollinator Health » Research » Research Project #431602

Research Project: Functional Trait Responses of Invasive Ludwigia Species to Contrasting Hydrologic Conditions

Location: Invasive Species and Pollinator Health

Project Number: 2030-22000-029-21-S
Project Type: Non-Assistance Cooperative Agreement

Start Date: Sep 15, 2016
End Date: Sep 30, 2020

Objective:
Ludwigia peploides and L. hexapetala are ranked globally as one of the worst aquatic invasive weeds. While the need for effective management approaches is growing, little is known about the biological and ecological capacity of these invaders to persist under changing environmental conditions. Extreme weather events, climatic flood and drought cycles, and anthropogenic management of water levels for water supply and recreational purposes subject aquatic macrophyte populations to a broad range of hydrologic regimes during their life cycles. Increased temperature and drought frequency as well as changes to watershed hydrologic regimes are expected with global climate change, and in recent years have been observed in invaded watersheds California. These environmental perturbations can have direct impacts on plant function. However, we still have a rudimentary understanding of how environmental change, ploidy level and reproductive mode of species, and functional plant trait responses to these processes will alter invasion dynamics in watersheds. Plant responses to stresses imposed by variation in hydrology may be influenced by ploidy level of the taxa, as polyploids are predicted to be more stress tolerant than diploids. In riverine wetlands of California, two emergent floating-leaved Ludwigia cytotypes (L. peploides, diploid; L. hexapetala, decaploid) have become increasingly invasive. The objective of this agreement is to develop and implement an experimental design to study these two cytotypes of Ludwigia established from apical shoot fragments in outdoor mesocosms under different inundation treatments (deep-flooded, shallow-flooded, gradual drawdown). The controlled experiment will be complemented by knowledge gained from observational data on plant phenology, soil moisture content and hydrologic conditions acquired at source population sites.

Approach:
In riverine wetlands of California, two emergent floating-leaved Ludwigia cytotypes (L. peploides, diploid; L. hexapetala, decaploid) have become increasingly invasive. The ARS – John Carroll University team will develop a randomized complete block experimental design to study these two cytotypes of Ludwigia established from apical shoot fragments in large outdoor mesocosms under different inundation treatments (deep-flooded, shallow-flooded, gradual drawdown). Survivorship and key phenological events (e.g. anthesis, seed capsule development) and soil moisture content will be recorded during the growth phase of the experiment. Prior to harvest, foliar gas exchange and leaf water potential will be measured on experimental plants. At harvest, we will separate plant tissue by anatomy and measure functional plant trait responses including total dry biomass, biomass allocation, leaf area, tissue chemistry, and stem node and root tissue porosity. Biomass allocation will be quantified as root mass ratio (RMR, root mass/total biomass; %), specific leaf area (SLA, leaf area/leaf mass;m2 kg-1), and leaf mass ratio (LMR, leaf mass/total biomass; %). Biomass allocation to reproductive tissue, plant tissue chemistry, and stem node and root porosity will also be assessed. The effects of hydrology and their interactions on final growth of each cytotype and ecophysiological and biochemical responses will be evaluated with MANOVA and post hoc tests. If the MANOVA is significant we will proceed with a two-way ANOVA with hydrology and cytotype as main effects and one interaction term (hydrology X interaction) for each response variable. A manuscript will be prepared for publication of results. During evaluation of this work, outstanding questions and approaches for future work may be identified.