Fertilized midrotation loblolly pine (Pinus taeda L.) response to yaupon (Ilex vomitoria Ait.) control and biomass partitioning and biochemistry of fertilized loblolly pine seedlings

Loblolly pine (Pinus taeda L.) response to altered environment was investigated in a field study and in a growth chamber study. Herbicide treatment targeting yaupon (Ilex vomitoria Ait.) was performed in two fertilized east Texas pine plantations located near Groveton and Zavalla. Treatment with a mix of triclopyr and imazapyr was effective in reducing the cover, basal area, number of stems, and total length of yaupon to less than 25% of untreated stands after two years. No consistent differences in pine foliar nutrients or in soil moisture were observed as a result of yaupon treatment. Pine leaf area index (LAI) was increased 0.14 units in the Zavalla plantation following treatment for yaupon. Pine diameter current annual increment increased from 1.24 cm to 1.42 cm and volume per tree current annual increment increased 10% in the Groveton plantation two years following treatment for yaupon.; Growth chamber grown loblolly pine seedlings subjected to two levels of nitrogen fertilization exhibited differences in biomass allocation and biochemistry after forty-eight weeks of treatment. Total seedling biomass (110 g) and height (72 cm) was similar between treatments, but seedlings fertilized with a higher rate of nitrogen had 11 g greater foliar biomass and 15 g less root biomass than seedlings fertilized at a lower "control" rate. Greater root mass, 49 g, occurred with low nitrogen than with high nitrogen, 34 g. These differences in resource allocation led to increases in shoot:root ratio and the biomass partitioning coefficient, k, under high nitrogen treatments. High nitrogen treatments resulted in lower sugar and starch concentration and greater amino acid concentration in mature foliage and roots, but not in juvenile foliage. The biomass partitioning coefficient was negatively correlated with the sugar to amino acid ratio in mature foliage and roots after forty-eight weeks of treatment (r = -.59, P = 0.0671 and r = -.68 and P = 0.0194). Sugar to amino acids ratios may be good indicators of differences in biomass partitioning of loblolly pine.