Native congeners provide biotic resistance to invasive Potentilla through soil biota.

Soil biota can facilitate exotic plant invasions and these effects can be influenced by specific phylogenetic relationships among plant taxa. We measured the effects of sterilizing soils from different native plant monocultures on the growth of Potentilla recta, an exotic invasive forb in North America, and conducted plant-soil feedback experiments with P. recta, two native congeners, a close confamilial, and Festuca idahoensis, a native grass species. We also reanalyzed data comparing the ability of P. recta to invade experimentally constructed congeneric monocultures vs. monocultures of a broad suite of non-congeners. We found that monocultures as a group, other than those of the native P. arguta, were highly invasible by P. recta. In contrast, this was not the case for monocultures of P. arguta. In our first experiment, the biomass of P. recta was 50% greater when grown in soil from F. idahoensis monocultures compared to when it was grown in soils from P. arguta or P. recta monocultures. Sterilizing soil from F. idahoensis rhizospheres had no effect on the biomass of P. recta, but sterilizing soil from P. arguta and P. recta rhizospheres increased the biomass of P. recta by 108% and 90%, respectively. In a second experiment, soil trained by F. idahoensis resulted in a positive feedback for P. recta. In contrast, soils trained independently by each of the two native Potentilla species, or the closely related Dasiphora (formerly Potentilla) resulted in decreases in the total biomass of the invasive P. recta indicating strong negative feedbacks. Soil trained by P. recta also resulted in intraspecific negative feedbacks. Our results demonstrate substantial negative feedbacks for an invader in its nonnative range under certain conditions, and that native congeners can mount strong biotic resistance to an invader through the accumulation of deleterious soil biota.

Prior hydration of Brassica tournefortii seeds reduces the stimulatory effect of karrikinolide on germination and increases seed sensitivity to abscisic acid.

BACKGROUND AND AIMS: The smoke-derived compound karrikinolide (KAR(1)) shows significant potential as a trigger for the synchronous germination of seeds in a variety of plant-management contexts, from weed seeds in paddocks, to native seeds when restoring degraded lands. Understanding how KAR(1) interacts with seed physiology is a necessary precursor to the development of the compound as an efficient and effective management tool. This study tested the ability of KAR(1) to stimulate germination of seeds of the global agronomic weed Brassica tournefortii, at different hydration states, to gain insight into how the timing of KAR(1) applications in the field should be managed relative to rain events. METHODS: Seeds of B. tournefortii were brought to five different hydration states [equilibrated at 15 % relative humidity (RH), 47 % RH, 96 % RH, fully imbibed, or re-dried to 15 % RH following maximum imbibition] then exposed to 1 nm or 1 microm KAR(1) for one of five durations (3 min, 1 h, 24 h, 14 d or no exposure). KEY RESULTS: Dry seeds with no history of imbibition were the most sensitive to KAR(1); sensitivity was lower in seeds that were fully imbibed or fully imbibed then re-dried. In addition, reduced sensitivity to KAR(1) was associated with an increased sensitivity to exogenously applied abscisic acid (ABA). CONCLUSIONS: Seed water content and history of imbibition were found to significantly influence whether seeds germinate in response to KAR(1). To optimize the germination response of seeds, KAR(1) should be applied to dry seeds, when sensitivity to ABA is minimized.

Relationships between growth, photosynthesis and competitive interactions for a C3 and C4 plant.

The relationships of photosynthetic characteristics to the competitive interactions of a C3 plant, Chenopodium album, and a C4 plant, Amaranthis retroflexus, were investigated in different temperature and water supply regimes. Both species had similar photosynthetic rates at 25°C, but at higher temperatures, Amaranthus had substantially greater rates than Chenopodium. Conversely, at lower temperatures, Chenopodium had an advantage. The competitive abilities in mixtures exhibited a close parallel to the photosynthetic performances with Amaranthus having an advantage at high temperatures and Chenopodium an advantage at low temperatures. These competitive outcomes were determined primarily by differences in relative growth rates prior to canopy closure. In the respective, temperature regimes, the species having the highest photosynthetic rate, which resulted an more rapid growth, overtopped and shaded the other species at the time of canopy closure. These results demonstrate that differences in photosynthetic temperature response between C4 and C3 plants can be an important determinant in competitive interactions, but at least in this case, the influence is primarily through, events prior to the actual initiation of competition.In contrast to temperature, growth of the plants under limited water supply had no influence on the competitive interactions. Thus, the presence of the C4 pathway alone was not sufficient to yield a competitive advantage over the C3 species under water limited conditions.