DOI: 10.5061/dryad.08kprr51c
title: How environmental stressors affect reproductive potential in a saltmarsh plant species Plantago maritima

description: We examined whether the presence or absence of different environmental
 stressors influenced the reproductive potential of a saltmarsh species –
 Plantago maritima. We focused on total seed output, seed quality and
 biomass of progeny. So far, there are no studies trying to answer the
 question of how different saltmarsh management affects the quality of seed
 in saltmarsh species. For the purposes of the study, plots subjected to
 light mowing, light or heavy grazing, trampling or rooting were designated
 in three nature reserves in Poland. On each plot, the abundance of
 infructescences per sq. metre was calculated. Mature infructascences were
 collected and their length and no of fruit capsules were measured. The
 seeds obtained from fruit capsules were weighted and sown in controlled
 conditions. The germination rate and the final germination percentage were
 calculated. A representative number of sprouts were grown. After a period
 of two months, the specimens were harvested and their total dry mass was
 measured. It was found that heavy grazing had the greatest effect on all
 of the studied characteristics. The presence of this factor resulted in
 shorter infructescences with a smaller number of fruit capsules. However,
 this phenomenon was compensated by the higher abundance of infructescences
 per sq. metre. At the same time seeds produced by grazed specimens were
 significantly lighter. Interestingly, intensive trampling by people
 affected Plantago maritima specimens in a similar way to heavy grazing,
 while mowing and rooting had less impact on the considered
 characteristics. Although a positive correlation between seed mass and
 germination success was found, the altogether lower seed mass had a
 negligible effect on germination parameters. Also, the differences in seed
 parameters did not affect dry mass of obtained progeny grown in lab
 conditions.
description: Samples were collected during the first week of September 2016 in the
 three populations of Plantago maritima. We selected a set of 72 plots that
 differed in the types of management: sites lightly mowed – mowed
 once/twice a year (MowL), lightly grazed – sites avoided by cattle, rarely
 grazed with higher vegetation (GrazL), heavily grazed – sites preferred by
 cattle with short vegetation (GrazH), heavy trampled – sites along the
 pathways intensively used by tourists (TramH), old marks of wild boar
 rooting – uneven surface, but almost completely overgrown by plants
 (RootOld), fresh marks of rooting – uneven surface with a significant
 share of bare soil (RootNew). Infructescence density per one sq. metre was
 calculated on every plot. Additionally, 254 infructescences (Table 1) were
 collected randomly from the plots, stored in envelopes and air dried for
 two weeks. After drying, the length of each infructescence was measured
 with a resolution of 1 mm and the number of fruit capsules were counted.
 The average length of infructescences was multiplied by their number per 1
 sq. m in order to estimate the potential for seed production per site
 (seed yeald). Germination test and growth experiment From each
 infructescence, a total of 30 randomly chosen seeds were weighed with a
 resolution of 1/100 mg. The seeds were subjected to stratification at 5 ˚C
 for 60 days, then planted in a growth chamber in germination tanks on
 filter paper. The germination regime was set with a 25 ˚C light(18h)/20˚C
 dark (8h). Light was supplied from warm white fluorescent tubes. The
 constant high moisture of the substrate was sustained with deionized water
 as it is known of Plantago maritima that its seeds germinate best in
 distilled water (Lotschert, 1970).The effects of germination – the number
 of emerging sprouts and their condition were checked daily for a period of
 14 days as it was determined that this period was enough for an average
 seed to germinate completely, and after that period almost no new sprouts
 appeared. The seeds were considered to have germinated when the radicle
 and two cotyledons were present. Mean germination time (MGT) was
 calculated by using the equation: MGT = ∑ (n × d) /N, where n = number of
 seeds germinated on each day, d = number of days from the beginning of the
 test, and N = total number of seeds germinated at the termination of the
 experiment (Ellis & Roberts, 1981). After germination, a
 representative number of sprouts (Table 1) for every variant of management
 were grown in a separate pots filled with organic soil. After a period of
 two months, just before the plants started allocating material to
 reproductive organs, the specimens were harvested, separated into
 underground and aboveground parts, and their dry mass was measured.
 Statistical Analysis To test the influence of the environmental stressors
 on each of the response variables eight multivariate linear regression
 models were performed. The statistical significance level of all
 regression coefficients and models were established as α = 0.05. All of
 the independent variables were coded binary, in which "1"
 represents the influence of a particular stressor and "0" – the
 absence of a particular stressor. In some cases, the response variables
 were influenced simultaneously by more than one stressor (by two: in 39
 cases by bough MowL and GrazH, in 4 cases - MowL and RootOld, in 4 cases -
 MowL * RootNew, in 4 cases - GrazH * RootOld, in 4 cases - GrazL *
 RootNew; by tree: in 4 cases - MowL * GrazL * RootNew) therefore all the
 stressors were tested simultaneously in one linear model. Depending on the
 skewness, the response data were normalized by logarithm log(x+1),
 square-root or square transformation (compare Table 2). To describe the
 importance of the environmental stressor influence, the percentage of each
 explained variation was calculated. Statistical analysis were performed in
 R (R Core Team, 2017), data visualisations were performed using ‘ggplot2’
 (Wickham, 2016) and ‘ggridges’ packages (Wilke, 2018) in R studio (RStudio
 Team, 2015). The correlations between measured variables were tested with
 the Pearson’s coefficient.
description: Data for: Lazarus et al. (2020). How environmental stressors affect
 reproductive potential in a saltmarsh plant species Plantago maritima.
 Contains 1 file: Plantago maritima_database - the whole database with all
 the measurements taken and analysed in Lazarus et al. (2020), How
 environmental stressors affect reproductive potential in a saltmarsh plant
 species Plantago maritima.