Conductance {pvldcurve}

Leaf Conductance

Description

Calculates mole-based or concentraction-based conductance (stomatal or minimal conductance) (mmol s^-1 m^-2 or mm s^-1) of the double-sided leaf area by experimental weight loss data and weather data

Usage

Conductance(data, sample = "sample", fresh.weight = "fitted.fw",
  date.and.time = "date.and.time", leaf.area = "leaf.area",
  humidity = "humidity", temperature = "temperature",
  atmospheric.pressure = 101.35, driving.force = "mole")

Arguments

data

data frame, with columns of equal length containg at least columns with time (and date) of the fresh weight measurements,the measured fresh weights (g) and the single-sided leaf area (cm^2) of the sample as well as the average relative humidity (%) and temperature (degree Celsius) during the measurement intervals. The data is to be ordered chronologically by sample. 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"

fresh.weight

optional name of the column in data containing the numeric fresh weight values (g); default: "fitted.fw" (fresh weight corrected by noises as outputted for leaf drying curves by the function FittedFW)

date.and.time

optional name of the column in data containing the time of the fresh weight measurements as class POSIXct; default: "date.and.time"

leaf.area

optional name of the column in data containing the numeric single-sided leaf area values (cm^2); default: "leaf.area"

humidity

optional name of the column in data containing the numeric humidity values (%); default: "humidity"

temperature

optional name of the column in data containing the numeric temperature values (degree Celsius); default: "temperature"

atmospheric.pressure

optional, giving the numeric atmospheric pressure in kPA, default = 101.325 (atmospheric pressure at sea level)

driving.force

optional; possible values: mole or conc; defines whether conductance is expressed on the basis of a mole fraction-based (default) or a concentration-based driving force

Details

Calculates mole-based conductance (mmol s^-1 m^-2) as:

g = T / VPD

whereas T = transpiration (mmol s^-1 m^-2) is calculated as:

T = \Delta FM * 1000 * (\Delta t * 60 * LA * 2 /10000 * 18.01528)^-1

whereas \DeltaFM = fresh matter reduction (g), \Deltat = time interval (min), LA = single-sided leaf area (cm^2) and VPD = vapor pressure deficit (mol * mol^-1) is calculated as:

VPD = (1 - RH / 100) * (VPsat / AP)

whereas RH = relative humidity (%), VPsat = saturation vapor pressure (kPA), AP = atmospheric pressure (kPA), whereas:

VPsat = 0.61121 * exp ((18.678 - T / 234.5) (T * 257.14 + T))

where T = air temperature (degree Celsius)

Concentration based conductance (mm s^-1) is derived from mole-based conductance g(mol) as:

g(conc) = g(mol) * R * (T + 273.15) / AP / 1000

whereas: R = gas constant (8.3144598 J (mol * K)^-1) and T = absolute temperature (degree Celsius)

Value

The original data frame extended by a numeric column with the mole-based or the concentration- based conductance (mmol s^-1 m^-2, mm s^-1) of the double-sided leaf area (conductance). The first value of each sample is NA since conductance values are computed from row i and i-1

Examples

# get example data
weight_loss_data <- leaf_drying_data
weather_data <- weather_data
df <- WeatherAllocation(weight_loss_data, weather_data)   # allocate weather to weight loss data

# extend the data frame by mole-based conductance values
df_with_conductance <- Conductance(df, fresh.weight = "fresh.weight")

# extend the data frame by concentration-based conductance values
df_with_conductance <- Conductance(df, fresh.weight = "fresh.weight", driving.force = "conc")

# calculate with atmospheric pressure of 99.8 kPA
df_with_conductance <- Conductance(df, fresh.weight = "fresh.weight", atmospheric.pressure = 99.8)