EFFECTS OF SOIL TEMPERATURE AND LIGHT INTENSITY ON ROOT GROWTH OF LOBLOLLY PINE SEEDLINGS

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Abstract
Both root growth and transpiration of Pinus taeda seedlings increased with increase in soil temp. from 5[degree] to 25[degree]C and decreased rapidly with increase from 25[degree] to 35[degree]C. Leaf:root ratios decreased with increased soil temp. from 5[degree] to 20[degree]C and increased with increase from 20[degree] to 35[degree]C. Sudden change in temp. from 20[degree] to 35[degree]C caused a brief period of accelerated growth and transpiration. Growth diminished to nearly zero 30 hrs. after the change. Roots became heavily suberized at 35[degree]C and required 6 days to resume growth after being changed to a soil temp. of 20[degree]C. Roots at 35[degree]C had a small embryonic region and no dividing cells. Starch accumulation in the root-tip region increased with decreased temp. No marked daily periods of growth were noted. The min. light intensity just sufficient for root growth was between 120 and 295 fc. Unit increases in light intensity produced much greater growth response at low than at high light intensities.