if plant hasn't reached maturity
calculate optimal biomass
adjust radiation-use efficiency for CO2
adjust radiation-use efficiency for vapor pressure deficit
assumes vapor pressure threshold of 1.0 kPa
adjust radiation-use efficiency for day length
compute temperature stress
compute n and p uptake and stresses
try water stress as function of precip/pet
code to turn off all plant stress code to turn off nutrient plant stress only reduce predicted biomass due to stress on plant reduce predicted biomass due to salt stress on plant (rtb salt) increase in plant c sum plant stresses