| Genetically improved loblolly pine (Pinus taeda L.) trees under intensive silviculture have demonstrated dramatic increases in wood production. However, increased input intensity has been associated with a higher propensity for certain genotypes to increase stem and branch deformities, as well as reduced disease resistance. The responses of several genotypes of loblolly pine to nutrient additions on stem sinuosity were assessed at three and twelve years of age in two different tests located in South Carolina and North Carolina, respectively.;The objectives of the studies were to assess the effect of nutrient additions and genetics on stem form, particularly stem sinuosity, in loblolly pine. Tissue samples from of newly expanding shoots at the beginning of growing season were taken and analyzed to assess the association between the nutrient concentrations on the tissues and stem sinuosity in five families from two provenances (Atlantic Coastal Plain "ACP" and Lost Pine Texas "LPT"). The second study was established at the ArborGen research facility near Summerville, South Carolina, with six different genotypes of loblolly pine to determine whether high N and low Ca availability caused sinuous growth. In early spring, eight blocks were fertilized with N as (NH4) 2SO4 and Ca as CaSO4. Nutrient concentrations from flushing shoot tissue were examined and then correlated with measures of stem sinuosity.;Results from the study of repeated nutrient additions in North Carolina showed that the addition of nutrients increased stem sinuosity, branch sinuosity, height, and the levels of N, P, K, Mg, Zn, B and S in the woody tissue of newly expanding shoots and decreased the levels of Mn and Cu. Calcium levels were the same in both treatments. Stem sinuosity was positively correlated with tissue nitrogen (N) concentration, while negatively correlated with manganese (Mn) levels. Negative family-mean correlations between N and Mn were found in both treatments (control and fertilized). There was a negative family-mean correlation between Mn and the height of the trees in the control and fertilized treatments. Differences in stem sinuosity and nutrient uptake were found among families within provenance, indicating a potential to reduce sinuosity by using genetic selection and appropriate nutrient additions.;The study in South Carolina where only N and Ca were added showed that nitrogen additions caused significant increases in both stem sinuosity and N concentrations. Calcium additions reduced stem sinuosity only when N was added, and did not significantly change in Ca concentrations in the flushing shoot tissue. Manganese (Mn), Ca, N and phosphorus (P) concentrations were all positively correlated with stem sinuosity.;The study from North Carolina showed also that in contrast with sweep, stem straightness, forking, and ramicorn branching were all negatively impacted (became worse) by the nutrient addition, especially in the LPT provenance. The ACP provenance showed 34% more susceptibility to fusiform rust than the LPT provenance.;Based on our findings, nutrient additions, especially N, increased not only stem and branch sinuosity but also increased the deformations in other stem traits such as straightness, forking, and ramicorn branching, and it also increased the proportion of the trees infected with fusiform rust. However, Ca addition reduced the negative impact of N addition on stem sinuosity. Provenance and family differences were also found.;Stem form traits are clearly affected by environmental differences and by genetics. This highlights the importance of matching appropriate site and cultural treatments with suitable genotypes. The choice of these three components has a large impact on the productivity and quality of the plantation. |
