HTLL: Hydrotime model with log-logistic distribution of base water...

In OnofriAndreaPG/drcSeedGerm: Utilities for data analyses in seed germination/emergence assays

Hydrotime model with log-logistic distribution of base water potential (Mesgaran et al., 2013)

Description

This model relates the time-course of the proportion of germinated seeds to the water potential in the substrate. It is based on a log-logistic distribution of base water potential within the seed lot. The equation is:

P(t) = \frac{1}{1 + \exp ≤ft\{ \frac{ \log ≤ft[ Ψ - ≤ft( \frac{θ _H}{t} \right) + δ \right] - \log(Ψ_{b} + δ) }{σ}\right\} }

In contrast to other hydrotime models (e.g., 'HTE1()', 'HTE2()', 'HTE3()', describing the distribution of germination time), this models describes the distribution of base water potential within the population, while the distribution of germination times is indirectly modelled, but it is not, in itself, gaussian (you see that 't' is at the denominator). The 'HTLL.fun()' is a generic function, which can be used for plotting or other applications, while the 'HTLL()' function is meant to be used for model fitting with the 'drmte()' function in the 'drcte()' package.

Usage

HTLL()
HTLL.fun(time, Psi, thetaH, delta, Psib50, sigma)

Arguments

The 'HTLL()' function has no arguments. The 'HTLL.fun()' function has the following arguments:

time	time
Psi	water potential in the substrate
thetaH	hydro-time constant
delta	shifting parameter to allow for negative water potential levels
Psib50	median base water potential
sigma	scale parameter for the log-logistic distribution

Details

The detail of this time-to-event model and the meaning of parameters are described in Mesgaran et al. (2013).

Value

The 'HTLL.fun()' function returns the proportion of germinated seeds, for any given values of time and water potential in the substrate. The 'HTLL()' function returns a list containing the nonlinear function, the self-starter function, the parameter names and other items which are internally used by the 'drmte()' function.

Note

This function is for use with the function 'drmte()'

Author(s)

Andrea Onofri

References

Mesgaran, M.B., Mashhadi, H.R., Alizadeh, H., Hunt, J., Young, K.R., Cousens, R.D., 2013. Importance of distribution function selection for hydrothermal time models of seed germination. Weed Research 53, 89–101.

Examples

data(rape)
modg <- drm( propCum ~ timeAf + Psi, fct=HTLL(), data=rape)
summary(modg)

OnofriAndreaPG/drcSeedGerm documentation built on March 14, 2023, 5:45 p.m.