Effects of plant competition, seed predation, and nutrient limitation on seedling survivorship of spotted knapweed (Centaurea stoebe)

AbstractPredicting site vulnerability to nonnative plant establishment remains a difficult goal. Seedling survival is an important component of population dynamics and can affect the success of control strategies. Field manipulations allow potential causal mechanisms of site vulnerability to be evaluated under realistic environmental conditions. We conducted field studies to determine the effects of plant competition and differing precipitation regimes on spotted knapweed seedling survival. We also examined the effect of herbivory on rosette survival and growth. Seeds were sown into plots with vegetation intact or removed at three sites. Seeds were also sown into plots where plant competition and precipitation were manipulated in a factorial design at a single site. Field studies demonstrated that site accounted for much of the variation in emergence rate, while herbivory and plant competition affected seedling survival rates. We observed a wide range in emergence rates, with site averages ranging from 13.1 to 42.5%. Survival the following year ranged from 0.5 to 9.4% of sown seeds. Rosette survival was significantly higher when herbivores were excluded from plots. Below average precipitation reduced seedling survival; however, even with supplemental water, dry-down of exposed sites resulted in low seedling survival. Of the 8,000 seeds added to plots in one study, by autumn, only eight plants resulted, seven of which survived in watered plots with intact vegetation. Collectively, these results show that seedling survival is a critical phase in spotted knapweed population dynamics and can vary among habitats on the basis of plant competition and precipitation. Furthermore, herbivory affects all stages of the lifecycle from the seedling onward. The observed differences help explain the reported variability in seedling survival in the literature and inform efforts to control spotted knapweed using plant competition and biological controls.

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Root volatiles in plant-plant interactions I: Characterization of root sesquiterpene emissions from Centaurea stoebe and their effects on other plants

10.1101/441717 ◽

2018 ◽

Author(s):

Valentin Gfeller ◽

Meret Huber ◽

Christiane Förster ◽

Wei Huang ◽

Tobias G. Köllner ◽

...

Keyword(s):

Spotted Knapweed ◽

Plant Interactions ◽

Centaurea Stoebe ◽

Positive Effects ◽

Root Volatiles ◽

The Impact ◽

Germination And Growth ◽

Plant Plant

AbstractVolatile organic compounds (VOCs) emitted by plant leaves can influence the physiology of neighboring plants. In contrast to interactions above ground, little is known about the role of VOCs in belowground plant-plant interactions. Here, we characterize constitutive root volatile emissions of the spotted knapweed (Centaurea stoebe) and explore the impact of these volatiles on the germination and growth of different sympatric plant species. We show that C. stoebe roots emit high amounts of sesquiterpenes, with estimated release rates of (E)-β-caryophyllene above 3 μg g−1 dw h−1. Sesquiterpene emissions show little variation between different C. stoebe populations, but vary substantially between different Centaurea species. Through root transcriptome sequencing, we identify six root-expressed sesquiterpene synthases (TPSs). Two root-specific TPSs, CsTPS4 and CsTPS5, are sufficient to produce the full blend of emitted root sesquiterpenes. Volatile exposure experiments demonstrate that C. stoebe root volatiles have neutral to positive effects on the germination and growth of different sympatric neighbors. Thus, constitutive root sesquiterpenes produced by two C. stoebe TPSs are associated with facilitation of sympatric neighboring plants. The release of root VOCs may thus influence C. stoebe abundance and plant community structure in nature.

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