TurgorLossPoint {pvcurveanalysis}

Turgor Loss Point

Description

Determines the x coordinate (RWD) of the turgor loss point in a set of experimentally obtained pressure volume curves.

Usage

TurgorLossPoint(
  data,
  sample = "sample",
  water.potential = "water.potential",
  RWD = "RWD",
  graph = TRUE,
  show.legend = TRUE
)

Arguments

data

data frame containing columns of equal lengths giving at least the numerical coordinates of the curve: water potential (MPa) and RWD (%), ordered by sample by descending water potential. A column containing the sample IDs is optionally required if several samples were measured.

sample

optional name of the column in data containing the sample ID, default: "sample"

water.potential

optional name of the column in data containing the numeric water potential values (MPa), default: "water.potential"

RWD

optional name of the column in data containing numeric relative water deficit values (%), default: "RWD"

graph

set FALSE if no plots are to be returned

show.legend

set FALSE if no legend is to be shown in the plots

Details

Before using this function, check the data for an initial plateau. Data points in the initial part of the water potential versus RWD plot with a stronger then expected decline need to be omitted.

The data is fitted using the Gauss-Newton algorithm of nls() to a combined exponential and linear model. The exponential and linear parts are extracted and RWD at turgor loss point is localized at their point of minimum distance.

Value

List splitted by sample consisting of

turgor.loss.point

coordinates of the turgor loss point (RWD)

formula

formula of the exponential and linear part of the combined fits

coef

coefficients of combined model

conf_int

upper (97.5 %) and lower (2.5 %) border of 95 % confidence interval of model parameters

If graph = TRUE, the plotted original data is displayed with the exponential and linear fit of the combined model as well as the x-coordinate (RWD) of the turgor loss point.

Examples

# get sample data
data <- RelativeWaterDeficit(pressure_volume_data)[pressure_volume_data$sample == 10, ]

# identify turgor loss point in curve
turgor_loss_point <- TurgorLossPoint(data)