One‐year‐old slash pine seedlings (Pinus elliottiiEngelm.) accumulated more radioactive phosphorus in needles at a 15–10°C day‐night temperature and 2500 foot candles than at higher temperatures and reduced light. Rate of phosphorus uptake was related to concentrations of ethanol‐soluble carbohydrates but not to those of starch or all carbohydrates. Results suggest that temperature and light can be important for optimum phosphorus nutrition of slash pine.