Functional trait responses of invasive Ludwigia species to contrasting hydrologic conditions

Authors: DRENOVSKY, REBECCA - John Carroll University; REICHOLF, REBECCA - John Carroll University; Futrell, Caryn; GALLEGO-TEVAR, BLANCA - University Of Sevilla; Grewell, Brenda

Submitted to: Weed Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 5/1/2018
Publication Date: 7/23/2018
Citation: Drenovsky, R.E., Reicholf, R., Futrell, C.J., Gallego-Tevar, B., Grewell, B.J. 2018. Functional trait responses of invasive Ludwigia species to contrasting hydrologic conditions. Weed Abstracts. [Abstract].

Interpretive Summary: Water regime is a major determinant of plant species occurrence and growth in wetlands. 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. Plant responses to these hydrological stressors may be influenced by ploidy level, as polyploids are predicted to be more stress tolerant than diploids. In riverine wetlands of California, two emergent floating-leaved Ludwigia cytotypes (L. peploides subsp. montevidensis, diploid; L. hexapetala, decaploid) have become increasingly invasive. We studied two cytotypes of Ludwigia established from apical shoot fragments in outdoor mesocosms under different inundation treatments (deep-flooded, shallow-flooded, gradual drawdown) and measured functional trait responses. Based on field observations, we predicted that the decaploid would be more tolerant of drying soils, and that both cytotypes would experience the greatest growth under shallow inundation. In contrast to previous studies, the decaploid sustained higher relative growth rates under all hydrologic conditions, but produced less biomass overall. However, the decaploid maintained longer shoot growth under all conditions, suggesting greater foraging potential for limiting resources, and greater potential for shoot fragmentation supporting vegetative reproduction. Under developing soil water deficit, having less biomass to support combined with a higher RGR and shoot length could help the decaploid find soil moisture more rapidly than the diploid. In contrast, the diploid rapidly transitioned to reproductive life stages in all treatments. Alternating wet and dry soil in drawdown zones can ultimately favor seed bank recruitment and diploid persistence.

Technical Abstract: Water regime is a major determinant of plant species occurrence and growth in wetlands. 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. Plant responses to these hydrological stressors may be influenced by ploidy level, as polyploids are predicted to be more stress tolerant than diploids. In riverine wetlands of California, two emergent floating-leaved Ludwigia cytotypes (L. peploides subsp. montevidensis, diploid; L. hexapetala, decaploid) have become increasingly invasive. We studied two cytotypes of Ludwigia established from apical shoot fragments in outdoor mesocosms under different inundation treatments (deep-flooded, shallow-flooded, gradual drawdown) and measured functional trait responses. Based on field observations, we predicted that the decaploid would be more tolerant of drying soils, and that both cytotypes would experience the greatest growth under shallow inundation. In contrast to previous studies, the decaploid sustained higher relative growth rates under all hydrologic conditions, but produced less biomass overall. However, the decaploid maintained longer shoot growth under all conditions, suggesting greater foraging potential for limiting resources, and greater potential for shoot fragmentation supporting vegetative reproduction. Under developing soil water deficit, having less biomass to support combined with a higher RGR and shoot length could help the decaploid find soil moisture more rapidly than the diploid. In contrast, the diploid rapidly transitioned to reproductive life stages in all treatments. Alternating wet and dry soil in drawdown zones can ultimately favor seed bank recruitment and diploid persistence.