Effects of nitrogen on leaf physiology and growth of different families ofloblolly and slash pine

Leaf physiology and fractional dry weight allocation were examined in four open-pollinated families of loblolly pine (Pinus taeda L.) and slash pine ( Pinus elliottii Englm. var. elliottii) in response to growth under low and high N supply for six months. Nitrogen greatly influenced dry weight alloca tion, total mass, leaf net photosynthesis and leaf conductance in seedlings of both species. Family variation in fine root allocation was observed und er low but not high N treatment, but for the majority of physiological and growth traits, family variation was stable under varying N treatment. Famil y rankings based on juvenile height, diameter and biomass accretion were si milar to rankings based on field performance at 22 years in slash pine but not loblolly pine. Lower leaf maintenance respiration rates were associated with families exhibiting the most rapid juvenile growth.