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. 2020 Mar 11;15(3):e0229726.
doi: 10.1371/journal.pone.0229726. eCollection 2020.

Environmental impact on the temporal production of chasmogamous and cleistogamous flowers in the mixed breeding system of Viola pubescens

Anne L Sternberger  1 , Anirudh V S Ruhil  2 , David M Rosenthal  1 , Harvey E Ballard  1 , Sarah E Wyatt  1   3
Affiliations

Environmental impact on the temporal production of chasmogamous and cleistogamous flowers in the mixed breeding system of Viola pubescens

Anne L Sternberger et al. PLoS One. .

Abstract

Viola pubescens is a perennial, mixed breeding herb that produces both chasmogamous and cleistogamous flowers at different times of the season. Once bud type is specified, it does not convert from one form to the other. While temporal production of the two flowers is known to be influenced by environmental factors, the specific environmental cues that signal emergence of each flower type have not been empirically studied. To investigate the environmental parameters driving seasonal development of chasmogamous versus cleistogamous flowers, a native V. pubescens population was examined during the spring and summer of 2016 and 2017. Measurements of light quantity, canopy cover, photoperiod, temperature, soil moisture, soil pH, and the number of chasmogamous and cleistogamous buds were collected on either a weekly or biweekly basis. Independent zero-inflated negative binomial (ZINB) regressions were used to model the odds of bud production (0 versus 1 bud) and bud counts (≥ 1 bud) as a function of the environmental variables. Results of the ZINB models highlight key differences between the environmental variables that influence chasmogamous versus cleistogamous bud development and counts. In addition to the ZINB regressions, individual logistic regressions were fit to the bud data. The logistic models support results of the ZINB models and, more crucially, identify specific environmental thresholds at which each bud type is probable. Collectively, this work offers novel insight into how environmental variables shape temporal development of chasmogamous and cleistogamous flowers, suggests distinct threshold values that may aid in selectively inducing each flower type, and provides insight into how climatic change may impact mixed breeding species.

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Conflict of interest statement

The authors have declared no competing interests exist.

Figures

Fig 1
Fig 1. Viola pubescens var scabriuscula bearing A) chasmogamous and B) cleistogamous flowers.
Photographs were taken over a native population in Sells Park, Athens County, Ohio.
Fig 2
Fig 2. Total number of chasmogamous (white bars) and cleistogamous (gray bars) buds recorded from ten plots in A) 2016 and 2017 and at each measurement date in B) 2016 and C) 2017.
Dashed vertical lines highlight bud type transition, the time at which chasmogamous budding ceased and the first cleistogamous buds were observed.
Fig 3
Fig 3. Seasonal photoperiod and averaged light quantity measured in A) 2016 and B) 2017.
At each measurement date, single photoperiod values were extracted from the nearest weather station, while five measurements of light quantity were taken per plot (n1 = 10). For graphical representation of light quantity, data were grouped by plot and date and averaged into single, weekly values for each plot. Boxplots represent the minimum, first quartile, median, mean (◇), third quartile, and maximum calculated on the weekly averages across plots. Dashed vertical lines highlight bud type transition, the time at which chasmogamous budding ceased and the first cleistogamous buds were observed.
Fig 4
Fig 4. Seasonal temperature data including averaged mean and standard deviation measured in A) 2016 and B) 2017.
For each of the 10 plots, temperature (°C) was measured at 15-minute (2016) and 1-hour intervals (2017). For data visualization, temperature data were grouped by measurement date and averaged to portray single, weekly observations encompassing the entire population. Error bars reflect the standard error, and dashed vertical lines highlight bud type transition, the time at which chasmogamous budding ceased and the first cleistogamous buds were observed.
Fig 5
Fig 5. Seasonal soil moisture data measured in A) 2016 and B) 2017.
From the ten plots, five measurements of soil moisture were taken per measurement date. For graphical representation, data were grouped by plot and date and averaged into single, weekly values for each plot. Boxplots represent the minimum, first quartile, median, mean (◇), third quartile, and maximum calculated on the weekly averages across plots. Dashed vertical lines highlight bud type transition, the time at which chasmogamous budding ceased and the first cleistogamous buds were observed.
Fig 6
Fig 6. Conditional plots representing predicted bud probabilities (P) of A) chasmogamous and B) cleistogamous buds developing as each environmental variable deviates by one-unit and while holding all other variables constant at their medians.
Rugs on the top of plots denote observations with positive residuals and bottom rugs reflect negative residuals.
Fig 7
Fig 7. Schematic of measurement days in 2016 and 2017 with corresponding bud types and environmental values that occurred at each date.
White arrows denote dates with chasmogamous buds and gray arrows are dates that cleistogamous budding was observed. L = average light quantity (μmol m-2s-1), P = photoperiod (hours), T = average mean temperature (°C), and S = average soil moisture (%).
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The authors received no specific funding for this work.