Acclimation of loblolly pine (Pinus taeda) foliage to light intensity as related to leaf nitrogen availability

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Abstract
The effects of soil N availability on the acclimation of leaves to light intensity was determined for loblolly pine trees (Pinus taeda L.) to test whether N addition would partly compensate for the negative effects of low light on photosynthesis. Shade treatment with 65% reduction of sunlight was applied to individual branches of N-fertilized (200 kg N.ha(-1)) and unfertilized trees. Acclimation of loblolly pine leaves to the changes in light intensity occurred in a relatively short period of time, with associated changes in photosynthesis and respiration. Loblolly pine leaves maintained a constant ratio of photosynthesis to respiration, regardless of light intensity. The acclimation of loblolly pine leaves to low light also involved a decrease in stomatal conductance, specific leaf weight, N content per fascicle, and chlorophyll alb ratio and an increase in chlorophyll content. N fertilization increased leaf N concentration and chlorophyll content, but did not increase photosynthesis and quantum yield. It is concluded that unless leaf chlorophyll is distinctly low, and quantum yield is significantly improved by increased chlorophyll following N fertilization, N fertilization will not offset the effects of low-light acclimation on photosynthesis of loblolly pine.

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