Stem growth and respiration in loblolly pine plantations differing in soil resource availability
Stem respiration and growth in 10-year-old loblolly pine (Pinus taeda L.) plantations were measured monthly during the third year of fertilization and irrigation treatments to determine whether soil resource availability differentially altered growth and respiration in stem tissue. Fertilized trees had significantly greater stem biomass, stem nitrogen concentration ([N]) and growth rate than unfertilized trees. Stem respiration (Rt) was significantly greater in fertilized trees when ex-pressed on a per unit surface area (Rt,a, µmol CO2 m-2 s-1 ), sap-wood volume (Rt,v, µmol CO2 m-3 s-1 ), or mass (Rt,w, nmol CO2 g -1 s -1 ) basis; however, there was no difference between treatments when expressed as a function of stem N content (Rt,n, µmol CO2 (mol N)-1 s-1 ). Irrigation had no significant effect on Rt or annual stem growth. Daily total respiration (Rd, mol CO2 m-2 day-1 ) and stem diameter growth both had a seasonal bi-modal pattern with peaks in early spring and midsummer. Stem [N] declined significantly during the growing season. Stem growth rate and [N] explaned 75% of the seasonal variation in temperature-normalized Rt,a.
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